CO >-
CO
[=OU_1 66362 J
OUP
552
7-7-66
10,000
OSMANIA UNIVERSITY LIBRARY Call No.
5S
7.
^2
Accession No.
2, J^ O/
Author
This boQ& should be returned
<>
or before the date
/fl&a.
McGRAW-HILL PUBLICATIONS IN THE BOTANICAL SCIENCES EDMUND W. SINNOTT,
Consulting Editor
A Textbook
of
SYSTEMATIC BOTANY
SELECTED TITLES FROM
McGRAW-HILL PUBLICATIONS IN THE BOTANICAL SCIENCES EDMUND W.
SINNOTT, Consulting Editor
Arnold An Introduction to Paleobotany Avery et al. Hormones and Horticulture
Babcock and Clausen Belling
The Use
Genetics
of the Microscope
Boysen Jensen and Avery and Burkholder Growth Hormones in Plants
Braun-Blanquet and Fuller and Conard Plant Sociology Eames Morphology of Vascular Plants
Eames and MacDaniels duction to Plant
An
Intro-
Anatomy
The Lower Fungi Gdumann and Dodge Comparative Fitzpatrick
Morphology of Fungi Haupt An Introduction to Botany Haupt Laboratory Manual of Elementary Botany Hill Economic Botany Botany Hill, Overholts, and Popp Johansen Plant Microtechnique Loomis and Shull Methods in Plant Physiology Lutman Microbiology
Maximov Miller
Plant Physiology Plant Physiology
Flowers and Flowering Plants Sass Elements of Botanical Microtechnique
Pool
Seifriz
Sharp Sharp
Protoplasm Introduction to Cytology
Fundamentals
Sinnott
Botany: Problems
of Cytology
Principles
Manual Laboratory Elementary Botany Sinnott and Dunn Principles
Sinnott
and for
of
Genetics
Smith
Cryptogamic Botany Vol. I, Algae and Fungi Vol. II, Bryophytes and Pteridophytes
Smith Fresh-water Algae of the U.S. Swingle Textbook of Systematic
Botany Weaver Root Development of Field Crops Weaver and Clements Plant Ecology
Wodehouse
Pollen Grains
There are also the related series of McGraw-Hill Publications in the Zoologiwhich A. Franklin Shull is Consulting Editor, and in the Agricultural Sciences, of which Leon J. Cole is Consulting Editor.
cal Sciences, of
DEVELOPMENT OF PLANT '.
.':
.:;
;.,;,.
A N G
i
o s P E R
M
LIFE
s ;
GYMNOSPERMS
FRONTISPIECE.- -Successions of plants, showing the estimated time of origin of the
differ,'
after Berry.)
nt groups
and the relative prevalence at different
periods.
(Modified
A
TEXTBOOK OF
Systematic Botany
6)>DEANE
B.
SWINGLE,
Ph.D.
Late Professor of Botany and
Dean
of the Division of Science
Montana
State College
Third Edition Fourth Impression
McGRAW-HILL BOOK COMPANY, NEW YORK AND LONDON 1946
INC.
A TEXTBOOK OF SYSTEMATIC BOTANY
COPYRIGHT, 1928, 1934, 1946 BY IHK
McGRAW-HiLL BOOK COMPANY, JklNTED
IN
THE UNITED STATES OF AMERICA
All rights reserved.
parts thereof, in
INC.
may
This book, or
not be reproduced
any form without permission of the publishers.
THE MAPLE PRESS COMPANY, YORK,
PA.
TO MY WIFE
WHO HAS BEEN MORE TO THIS BOOK
THAN COAUTHOR
PREFACE TO THE THIRD EDITION When the first edition of this book was published in 1928, it was the only work in which the principles and procedures of taxonomic botany had been assembled in textbook form for classroom use. Prior to that time students in this field had learned to name plants mostly by the apprentice system, sometimes supplemented by informal rarely by formal lectures. The situation was aptly stated by A. S. Hitchcock, himself a teacher for many ' ' Descriptive Systematic Botany years, in his published in 1925. 'Descriptive taxonomy at present may be likened to a
which the art or technique has not been committed to is handed down by tradition.' but writing Again in the text he craft, in
'The student's first experience in the general identification of plants may be obtained while he is serving as an assistant in botany at a college or an experiment station.' states,
Since that time, the situation has radically changed.
Students botany have always wanted a textbook in this field, and belatedly teachers of the subject are becoming 'textbook-minded.' They now realize that even good formal lectures
in systematic
need to be supplemented by a textbook here as in other branches of science, and that fragmentary assignments to technical literature do not serve the same purpose to beginners. This third revision has involved two major problems: (1) the sequence in which the topics should be presented, and (2) the determination of what should be presented in an introductory course and what should be reserved for advanced work.
As
sequence of chapters, the principal change in this revision has been to introduce the actual study of plant groups earlier, deferring the more abstract principles until later in the for the
course.
the
first
However, the subject matter is so organized that, after two chapters have been studied, the others can be taken
up in almost any sequence. The choice of material to be included in the book is more difficult, and some things are included that most beginning This statement applies especially to the reports of recent taxonomic researches and to references to books that undergraduates have little occasion to consult. However,
students will not use.
there
is little
demand
for
a textbook of advanced taxonomy, vii
fco it
PREFACE TO THE THIRD EDITION
viii
seems best to include some of these references here, to be referred to in later courses.
Teachers of plant taxonomy have not yet settled down to anything approaching a standard method of introducing this subject to the students. Probably there is more difference here in the
method of approach than in any other branch of science. The author has made a special effort, through correspondence with many distinguished botanists, to produce a book that will satisfy the requirements of most teachers of taxonomy. The question ' of geneticists and of including the 'experimental method ecologists in an introductory book while that subject is so new
and
advanced prerequisites is a difficult one. It has been explaining the method and its accomplishments and
calls for
solved
by
an elementary way in appropriate places, parI, X, and XII, and leaving the further development of it for advanced courses. Most of the chapters have been thoroughly revised and amplified, some almost entirely rewritten, and a new one has been added on methods of identification; but at the same time an effort has been made to keep down the size and cost of the book so that it will not be prohibitive for the student to buy both it and the necessary manual for the identification of his collection.
limitations in ticularly in
Chaps.
This opportunity
is
taken to express the author's gratitude
for the help given in the revision
by a number
of taxonomists.
Especial thanks are due to Dr. David D. Keck of the Carnegie ' Institution for his help in presenting the experimental method/' which lies in his field of research; Dr. George H. M. Lawrence of the Bailey
Hortorium, Cornell University, for valuable sug-
gestions on almost every chapter; Dr. Lincoln Constance and Dr. Willis L. Jepson of the University of California; Dr. Herbert F. Copeland of Sacramento, California Junior College; Dr. H. T. Darlington of Michigan State College; Dr. H. R. Totten of the University of North Carolina; Dr. J. M. Greenman and Dr. Edgar Anderson of the Missouri Botanical Garden; Dr. Aaron J. Sharp of the University of Tennessee; Dr. George Neville Jones of the University of Illinois; Dr. W. E. Booth, Montana State College; and Mrs. Lois Payson, librarian of Montana State College, for her indispensable help on the literature of systematic botany.
BOZEMAN, MONT., January, 1944.
DEANE
R
SWIN GLE.
PREFACE TO THE FIRST EDITION It is a matter of more than passing interest that in the oldest branch of botany comparatively little attention has been given to methods of presentation to the student. While the teaching of most botanical subjects in our colleges is on a par with that of other branches of learning, the teaching of taxonomy, especially
that of the higher plants, is not always a credit to the profession. Too often highly trained specialists, with a vital interest in their collections and an intense zeal for precise distinctions and
accurate determinations,
are
content to lead their students
through the paths of the apprentice, with little regard for anything but the technique of collecting, preserving, and naming, and certainly with little attempt to unfold to them in logical sequence the underlying principles of this branch of botanical science. Of late, a few teachers are giving lectures on the principles fundamental to systematic botany, but lectures not
supplemented by assigned reading are wholly inadequate for the beginner. In the field of general botany we have a wealth of textbooks, some of them splendidly written; and in plant physiology, histology, ecology, and even in the newer fields of cytology and phytopathology a few good texts can be found. But while the naming and classifying of plants have been going on for centuries, no textbook is available that adequately sets forth the principles of taxonomy and nomenclature. 1 A number of good reference books there are, to be sure, and many valuable papers on most phases of the subject. International congresses have been held to encourage uniformity in We have good systematists, and others principle and practice. are being reared to take their places. Notwithstanding these is to bring systematic available textbook no however, facts,
The author has not overlooked two books of especial value in this conThe first is J. C. Willis* 'Flowering Plants and Ferns' which contains some valuable information on principles and methods. The ' second is A. S. Hitchcock's 'Descriptive Systematic Botany published in 1
nection.
1925. Professor Hitchcock's book is especially valuable in its up-to-date treatment and its well-chosen topics fundamental to modern taxonomy and nomenclature. From the preface and the method of treatment, however, it is evidently intended as a reference book rather than a classroom text.
ix
PREFACE TO THE FIRST EDITION
x
botany to the student in logical and pedagogical form. this reason only that these pages are written. This book is an outgrowth of a course given at the
It
is
for
Montana
State College for the last fifteen years. It is designed to cover one semester, preferably the second, so that the fundamentals
be established during the colder months, and supplemented work with the opening of spring. Systematic botany should be preceded by a course in general botany, without which the student will fail to grasp the fundamental principles of phylogenetic taxonomy and will find that the examples used
may by
field
and meaningless. not intended that this text shall in any way supplant the manuals used for identifying plants. These are already numerous and cover the flora of practically every part of the country, are mostly unfamiliar It is
though lacking somewhat in harmony of detail, and this book is to supplement rather than to compete with them. The purpose of the first part is to set forth and illustrate the The principles and rules on which systematic botany is based. second part describes some sixty families of spermatophytes, chosen because of their size, economic importance, or peculiar To secure best results, a considerable portion of the interest. time must be given to laboratory and field work, chiefly devoted to actual identification of the local flora by the use of the keys and
manuals best suited to that
locality. this opportunity of expressing his gratitude aided in the work, either through valuable sug-
The author takes to
all
who have
gestions or the use of their libraries, and especially to R. A. Harper of Columbia University, J. E. Kirkwood of Montana
State University, Ernst A. Bessey and H. T. Darlington of the Michigan Agricultural College, A. S. Hitchcock of the U. S.
Department
of Agriculture, M. L. Fernald of Harvard University, of the University of Wyoming, Alfred Gundersen
Aven Nelson
Brooklyn Botanic Garden, and R. Fitzpatrick of the University of Nebraska. of the
J.
DEANE BOZEMAN, MONT., February, 1928.
Pool and T.
B. SWINGLE.
J.
CONTENTS PAGE Preface to the Third Edition
vii
Preface to the First Edition
What
ix
xv
Is Systematic Botany?
INTRODUCTION
1
CHAPTER EVOLUTION Ideals
IN
in
I
RELATION TO TAXONOMY
classification,
8.
Paleontological record, 12.
8
Evidences of evolution, 10. Acceptance of the doctrine of
Mechanism of evolution, 19. Accomplishevolution, 17. ments of evolution, 24. Progressive and regressive development, 25.
CHAPTER
II
THE IDENTIFICATION OF FLOWERING PLANTS 30 The structure of keys, 33. identification, 32.
METHODS USED
IN
Keys for Troublesome variations and exceptions,
The
plants and plant groups, 37. work of specialists, 43.
CHAPTER
36.
Portrayal of
floral chart, 40.
The
III
THE PREPARATION OF HERBARIA Purposes
Methods
of herbaria, 45. of preservation, 48.
45
Methods
of
Labeling and
CHAPTER
collecting,
46.
field data, 53.
IV
THE TERMINOLOGY OF SYSTEMATIC BOTANY Roots, 56.
Stems, 56.
cences, 63.
Flowers, 65.
Buds, 58.
Leaves, 58.
Fruits, 71.
55 Inflores-
Seeds, 73.
CHAPTER V GENERAL FEATURES OF SPERMATOPHYTA Classification of seed plants, 75. Class Gymnospermae, 76. 75.
Subclass
Dicotyledones,
76.
Subclass
76, xi
74
Division Spermatophyta, Class Angiospermae, 76.
Monocotyledones,
CONTENTS
xii
CHAPTER VI
PAGE
FAMILIES OF GYMNOSPERMS
77
Order Bennettitales, 80. Order Order Cordaitales, 82. Order Ginkgoales,
Order Cycadofilicales, 79 Cycadales, 81. 82.
Order
86.
Cupressaceae, 88.
.
Coniferales, 83.
Pinaceae, 84.
Order Gnetales,
CHAPTER
Taxodiaceae,
89.
VII
FAMILIES OF DICOTYLEDONS '^Magnoliaceae, 99.
94.
v^ymphaeaceae,
106.
91
Berberidaceae, 102.
97.
^Malvaceae,
Ranunculaceae, Ulmaceae,
104.
Geraniaceae, 108. 113.
Linaceae, 109. ^utaceae, 111. Violaceae, 115. VKapaveraceae, 116.
N^tuphorbiaceae, ^IJructferae, 117. Caryophyllaceae, 120. 121. 123. Salicaceae, Polygonaceae,
Chenopodiaceae, 125.
Ericaceae,
132. ^Asclepiada^O.^'Oleaceae, ceae, 133. ^Convolvulaceae, 135.*^olanaceae, 137. ^'feoraOrobanchaceae, ginaceae, 139.l^>crophulariaceae, 140. 142.vtabiatae, 144. Rosaceae, 145. Pomaceae, 148. 128.
Gentianaceae,
Drupaceae, 149.^Leguminosae, 151. Saxifragaceae, 157. Grossulariaceae, 158. Onagraceae, 159.^^Iucurbitaceae, 161. Cactaceae, 163. Vitaceae, 165.V^Loranthaceae, 167. Aceraceae, 168. VXnacardiaceae, 171. Juglandaceae, 171. Fagaceae, 175. Betulaceae, 179. Cornaceae, 182. ^Cmbelliferae,
184.
^ubiaceae,
187.
Caprifoliaceae,
188.
%/Compositae, 189.
CHAPTER FAMILIES OF
VIII
MONOCOTYLEDONS
194
Alismaceae, 195.^Liliaceae, 196. Juncaceae, 199.UAra-* Cyperaceae, 202.iXJramiceae, 200. -Palmaceae, 202. neae,
205.
Comparison of three
plants, 211.
families
of
grass-like
Iridaceae, 211./Orchidaceae, 212.
CHAPTER IX NOMENCLATURE
217
Relation of nomenclature to taxonomy, 217. Common names, 217. Botanical or scientific names, 219. Nonvalid names, 222.
Citing authority for names, 226.
Efforts
CONTENT*
xiii
PAGE
toward
International botanical conuniformity, 228. 228. 'The gresses, type concept, 231. Digest of rules of botanical nomenclature, 234. Effects of rules of nomen-
clature, 236.
CHAPTER X PRINCIPLES OF
TAXONOMY
237
Difficulties in classification, 237.
Bases of taxonomy, 242.
Plan of taxonomy, 249.
Categories used in taxonomy, 249. The newer species concept, 253. Subspecific categories, 256. Contributions of other branches of botany to taxon-
omy, 259. The experimental method in taxoYiomy, 262. Major and minor characters, 264. Clear-cut versus intergrading characters, 265. Homologs versus analogs, Characters of Spermatophyta, 269.
267.
Morphological
indicators of phylogeny, 276.
CHAPTER XI SYSTEMS OF
TAXONOMY
281
Pre-evolutionary systems of taxonomy, 281. Taxonomic development in southern Europe, 282. Taxonomic de-
velopment in central Europe, 283. of
and
Bessey,
status of
Evolutionary systems
Comparison of the systems of Engler
taxonomy, 288.
Competition of systems, 300.
296.
Present
classification, 302.
angiosperm
CHAPTER
XII
THE LITERATURE OF SYSTEMATIC BOTANY Media
for
taxonomic publication, 305.
Fundamental damental principles
306.
The
305 early classics,
morphological, 307. FunRules of botanical genetic, etc., 309.
principles
World floras and taxonomic systems, and manuals, 316. Taxonomic treatCultivated and economic groups, 319.
nomenclature, 312. 314.
Regional
ment
of limited
plants, 322.
floras
Non-technical
Indexes, catalogues,
Index
etc.,
floras, 324.
327.
Paleobotany, 326.
Miscellaneous, 329.
331
WHAT
IS
SYSTEMATIC BOTANY?
Systematic botany is the science of classifying and naming Plant taxonomy lays emphasis on classification as an
plants.
of phylogenetic relationships, and nomenclature each species with a name. provides Systematic botany includes both. Some people's interest in systematic botany is satisfied by a knowledge of the local flora and an ability to identify it, an interest that has been widened by automobile travel. This is but a limited aspect of a large subject. Important work in this field is the building of great herbaria with specimens from all over the world classified chiefly by comparative morphology. A newer taxonomic outlook is the study of the progress of evolution
expression
through experimental work, by crossing plants of different degrees of relationship, studying the products under different environmental conditions, and noting their establishment as new species or subspecies or their failure to survive for genetic or ecological reasons.
The modern systematic
botanist, if he is to go far in his needs a profession, good background in general botany, cytology, genetics, ecology, plant geography, and paleobotany; otherwise, he can only collect, name, preserve, and catalogue plants, without understanding their origin. This is all the amateur systematists and some professionals attempt to do. Obviously the students of systematic botany need to devote years of time to the subject, and teachers are much at variance as to the sequence in which the different topics should be pre-
sented.
The
trend, however,
is
toward having
classes in the first
plants as possible, know the principles involved, and receive an introduction to the newer experimental methods of geneticists and ecologists, which are not
course become familiar with as
many
yet well enough established to be presented in dogmatic form. Advanced courses in systematic botany should keep in close touch with research in all related fields.
A TEXTBOOK OF SYSTEMATIC BOTANY INTRODUCTION Modern systematic botany holds a unique position. It is in a science with its own ideals and its own rules and principles. The orderly classification of the wealth of vegetation that adorns the earth, a terminology understood by all nations, an application
itself
of the laws of evolution
of
man's best
efforts.
these things in themselves are worthy however, another service to per-
It has,
It must aid those in other fields of endeavor, who make use of plants for many purposes, to know the identity of the kinds they use and their relationships to others.
form.
Nomenclature deals with names, which
may
or
may
not indi-
seeks to group plants on a basis of similarities and differences, these being, as we now believe, expressions of actual phylogenetic relationships 'blood relaWe might conceivtionships' as we say of the higher animals. cate relationships.
Taxonomy
ably have names without classification, but we can scarcely have classification without names. Indeed, names are necessary in almost any kind of discussion. Particularly close is the relationship between systematic botany and ecology. Names have little interest in themselves. It is
only when attached to objects of study that names become
The out-of-door botanist not only names the plants significant. but also notes their distribution, environment, seasonal development, and characters suggestive of economic value.
EARLY BOTANICAL
WORK
IN
AMERICA
In America the development botany in all its aspects has first The been an interesting one. distinguished American botanist was John Torrey, who, after graduating from the College of Physicians and Surgeons in New York, found greater interest in plants than in medicine and became New York State Botanist in of
1
A TEXTBOOK OF SYSTEMATIC BOTANY
2 1836.
He
established
two
journals, the Flora of the State of
New
York and Flora of North America and helped to start the young Asa Gray on his career in botany. The Torrey Botanical Club with its two publications, the Journal of the Torrey Botanical Club and the Torrey Botanical Club Memoirs, testifies to the great esteem in which he was held by the younger botanists of his time. America's great pioneer systematic botanist, Asa Gray, after graduating in medicine and gaining an inspiration and much botanical knowledge from John Torrey, studied for a time with the more experienced botanists of England and returned to this country, where he was made Professor of Natural History at Harvard University, a position that he held up to the time of his death in 1888. He found in this country a veritable paradise, a vast and little-explored region with many familiar forms and not a few that were new to science. His tireless efforts, boundless enthusiasm, keen discrimination, and sympathetic attitude endeared him to his students and associates. It is little wonder that his modest laboratories became a Mecca for American botanists, both professional and amateur. ,
Gray's influence was far-reaching, especially as it came during a period when many were becoming interested in work on the
new country. In colleges and universities the taxonomic aspect of botany became almost an obsession. The making of herbaria dominated botanical departments. Dr. Gray had sought to have centered at Harvard University a wellbalanced series of courses in botany, including morphology and physiology, but the general enthusiasm ran irresistibly into the taxonomic field. As a result, many in the next generation of botanists used and taught this branch almost to the exclusion of others. This was quite unfortunate, for the impression was that the chief purpose of botany was to collect and name given plants. Indeed, in the minds of many people botany meant nothelse. Such an objective alone could hardly meet the approval ing of the masses, and botany lost favor accordingly. Appropriations were grudgingly given, and many students resented the courses where the practical value was not obvious. Fortunately, America produced a few great men who, in addition to being distinguished systematic botanists, had a broad outlook on the entire field of botany and were truly inspiring teachers. The strenuous flora of this
efforts of Charles E, Bessey,
W.
A, Kellerman,
W.
G. Farlow,
INTRODUCTION John M. Coulter, and others soon restored the balance of emphasis in the colleges, and, indeed, the pendulum again swung too
Many of the herbaria were stored away, classification ceased to be taught, and hundreds of students graduated from botanical courses without knowing the names of even a score of
far.
plants and without ever having attempted to use an analytical The layman, however, moving more slowly, continued to key. believe that
FIG.
1.
botany had its beginning and end
Asa
Gray
(1810-1899).
Great pioneer systematist of Harvard University and inspiration to many American botanists. (Courtesy of Alfred Gundersen, Brooklyn Botanic Garden.)
in nomenclature.
FIG. 2. John M. Coulter (18511928) Systematist and morphologist, and inspirational teacher. For 30 years head of the department of botany in the University of Chicago. He was highly instrumental in establishing botany in America on a broad .
basis.
(Courtesy of Alfred Gundersen,
Brooklyn Botanic Garden.)
r
Systematic botany in this country has now found its proper It has its place with the other branches of botanical science. students include it in most botanical trained specialists, highly their curricula,
and the amateur
finds in
it
his chief source of
delight.
Fortunately, the antiquated methods of teaching systematic botany by the apprentice method are being replaced by the more lectures, laboratory work, and field trips and in the principles of taxonomy and the student grounding the
modern ones using
A TEXTBOOK OF SYSTEMATIC BOTANY
4 rules of
nomenclature that have made botanical science as a whole
a subject of respect.
PURPOSES OF SYSTEMATIC BOTANY The
absolute dependence of
man upon
plants, the
many
kinds
that he uses, and the varied purposes he finds for them have long made the necessity for plant names of some kind imperative. To primitive peoples, who were content to apply some kind of name to only those species that were especially useful, harmful, or interesting,
and who traveled but little, relationships of species of. Just a few simple names served every
were rarely thought
purpose. However, the application of scientific thinking to considerations other than economic called for a more orderly procedure. It should be clearly understood at the outset that the study of systematic botany involves two major procedures: (1) the establishing of the relationships that exist naturally between many
the giving of names, common or groups or kinds of plants. The first is called taxonomy and the second nomenclature. The scientific mind is not content with names alone. If we study any group of objects, from atoms to heavenly bodies, we inevitably endeavor to This orderly arrangement is classify the members of the group.
groups of plants, and
(2)
scientific or both, to all
the
first
step in scientific treatment. botanist finds about
The systematic
him
millions of individual
No two
are exactly alike, yet some are nearly so, while plants. others are so different that they show scarcely any bond of rela-
By noting and comparing the similarities and differmakers of this science have brought out of chaos a the ences, Thus a profession has been set up in which fairjy orderly system. the specialist, by establishing names and descriptions of thousands of specimens, performs a service to all who deal with plants. tionship.
He
determines their group relationships, their distribution, properties, and other points of interest. Systematic botany forms a groundwork for all sciences dealing with plants.
The myriad uses of plants make it necessary for many people who are not taxonomic specialists to have some knowledge of When we consider that green plant names and classifications. plants offer the greatest means of utilizing energy from the sun, that plants directly or indirectly furnish most of our food, cloth-
INTRODUCTION
5
ing, shelter, fuel, medicine, paper, decorative materials, and many other useful things, we are made to realize that an orderly classifi-
cation of them, understood in some measure by all civilized people, does much to prevent confusion and to facilitate cooperative effort.
Very extensive use of systematic botany is made in Every kind of tree must be named and classified, and its characteristics, distribution, and abundance must be learned. But forestry is not limited to the production of lumber. The Forestry.
forestry.
national forests are extensively used for the grazing of livestock; and those who control the leasing and use of forest lands for this
purpose must be familiar with all forms of vegetation and must know the palatability and food value of each kind, its methods of propagation, and the amount of grazing it will stand without danger of depletion. Furthermore, increasing use is made of the forests for recreational purposes, and national parks and forestry
some with beautiful on the plants and shrubs that are most attractive to
services are publishing splendid bulletins, illustrations, visitors.
Agriculture, Horticulture,
and
Floriculture.
In the broad
field
of plant breeding extensive progress has been made in recent years in the securing of improved varieties of grains, fruits, flowers, etc. This is not accomplished by haphazard tests but follows definite
Crossing
procedures.
and
varieties
is
usually involved, and a knowledge of is required to secure
from a world standpoint
species Even varieties resistant to suitable stocks for the purpose. diseases that can be controlled by no other method have been
secured in this way.
mostly by men
Foreign seed and plant introduction
is
done
well versed in systematic botany.
Range Management. As the years go by, the American people more conscious of the fact that our once fertile and prairie, are being exploited to a point wooded both lands, where erosion and dust blowing, added to a depletion of humus and of inorganic food materials especially nitrates, phosphates, and potash by cropping have become national problems. Courses in range management are being established that make more study of plant life than of livestock. We are coming to realize that the conservation of native grasses and other plants and the selection of species best suited for holding the soil call for the efforts of ecologists who are well trained in systematic are becoming
A TEXTBOOK OF SYSTEMATIC BOTANY
6
botany.
Indeed, forestry and range
management
furnish the
greatest practical application of this branch of botanical science. Ecology. The character of the vegetation has long been known
Certain species are definitely hydrophytic, xerophytic, or halophytic, and soil characters of all kinds may be indicated by the vegetation growing on the as a valuable index of soil conditions.
surface.
In
many
cases good ecologists can quickly interpret the its vegetation, with little or no study
character of a land area by of the soil itself.
The plant ecologist must be a close student of systematic botany, knowing both the names of plants and their relationships, for his conclusions with regard to the effects of environment and the succession of species on an area would be wholly misleading if applied to species or groups different from the ones specified. helpfulness of systematic botany and ecology is mutual, as explained later, a wholly new conception of plant species
The for,
and
their evolutionary origin is coming from a combination of and ecological studies made by crossing related plants and
genetic
studying the resulting products. Paleobotany. One of our greatest difficulties in tracing relationships of plants and animals is that the ancestral forms con-
The scattering fossils necting existing species have disappeared. that are found here and there, though presenting a fragmentary picture, are very useful in revealing the characters of these ancesforms and have real significance to those who have for a background a knowledge of taxonomy. Much of the research in taxonomy is concerned with piecing together the discoveries in paleontology, genetics, cytology, and other branches of science into a working plan of classification. In many groups classification has proceeded only far enough to associate certain forms of life that have a kind of resemblance that may or may not represent actual relationship. The systematic botanist has not yet reached the place where he can afford to be His classification must be flexible and frequently revised static. to embody new information and to adjust itself to the newer viewIf he takes this progressive attitude he can be of tremenpoints. dous service in summarizing and utilizing the discoveries of He has a duty beyond the mere investigators in related fields. tral
naming
From
of plants.
the foregoing
it will
be seen that collecting the flowering
INTRODUCTION
7
plants of a limited region and learning their names is but a simple and superficial part of the science of systematic botany.
With the growth of the different sciences a desire on the part of many people to study them from the amateur's standpoint. Probably no other science, except possibly geology, has so captured the interest of the amateur as botany. Such studies could be made in any field of this science, but systematic botany is the one with the greatest appeal. This is largely due to the fact that it gives an opportunity for satisfying the human desire to collect. While some amateur collections of plants serve only a temporary purpose, others are of great value Amateur Botany.
there
is
and contain thousands
of
specimens accompanied by important
ecological data. Usually such collections are finally donated to educational institutions where they will be protected from fire and
other destructive agencies. More and more the spirit of service
is
pervading the
scientific
With increasing effectiveness representative men in each science will apply their work and that of their colleagues to everyworld.
day life. In harmony with this tendency, the systematic botanist of tomorrow will add to the names and classification of plants
much
information of value to the
human
race.
CHAPTER
I
EVOLUTION IN RELATION TO TAXONOMY Several bases of classification have come into use, each designed to serve a special purpose. Some of these grew out of the economic uses of plants; others were founded on gross structural
resemblances such as habit of growth trees, shrubs, vines, and All these systems were fragmentary and incomplete, and those plants that did not fit the classification or had a different For example, plants not regarded as interest were ignored. medicinal received little consideration by the early herbalists. At the present time many wild plants that are not known to be either beneficial or harmful to agriculture are ignored even by those whose scientific training in agriculture has included considerable botany. Only one system of classification has made any pretense to completeness, and that is the one now in use which is based on natural relationships. Before the conception that existing species originated by evolu' ' tion had been proposed, natural relationships among plants and among animals were described. Certain families such as the Umbelliferae, Compositae, Gramineae, and Leguminosae were herbs.
recognized through morphological similarities in flowers, inflo' rescences, leaves, etc., but the expression 'natural relationship did not have the significance that it now has. It meant merely That the early conceptions of relationship similarity of parts.
among ogy
is
living things were based largely on comparative morpholfortunate, for this has been found to be one of the best
criteria of phylogenetic relationship.
IDEALS IN CLASSIFICATION There are three conceptions of classification that must be understood in studying systematic botany. 1. Natural classification refers to the relationships that exist among plants as a result of evolutionary development, regardless of man's knowledge of the subject. These natural relationships 8
EVOLUTION IN RELATION TO TAXONOMY actually exist and would exist earth to study them. 2.
Taxonomic
9
there were no
human
beings on
classification is the result of
man's
efforts to
if
express or describe natural classification and put it into form for discussion and use. Inevitably it ib imperfect, incomplete, and it is built on incomplete evidence and even personal opinion concerning natural classification. 3. Artificial classification is a grouping, generally for convenience, that does not pretend to express natural relationships. Often it is the result of using a single character as a basis for classification rather than a combination of characters, which is now
subject to improvement, for
recognized as the surer method of bringing out actual relationMaking a single class that would include all thallophytes,
ships.
or
all
spermatophytes that lack chlorophyll, but no others would an artificial group.
result in
Methods of Classification. The ideal classification must embody two qualities. It must show actual phylogenetic relationships, use.
and
If it fails
to
must be reasonably convenient for practical show true relationship, it is artificial and does
it
not satisfy the discriminating thinker, although it may be conToo often, however, as in the bacteria and some
venient for use.
groups of fungi and algae, an artificial grouping has had to suffice until a taxonomic classification could be perfected. If, on the other hand, a natural system is too involved and too difficult of comprehension, and especially if, in addition to these faults, the phylogenetic evidences are incomplete and debatable, such a system fails to gain general acceptance and may have to give way, at least temporarily, to one that is more artificial. Many botanists believe that different classes of fungi originated
from as
each other and that a many groups natural phylogenetic classification should show a closer relationship between certain fungi and certain algae than between the different groups of fungi. Nevertheless, they continue in actual if they were a homogeneous unit. treat as the to practice fungi One of the advantages of a phylogenetic classification over an artificial one is that it is safer to generalize in related groups than in unrelated ones. For example, if one is well informed concerna few ing species of Pinaceae, Gramineae, Leguminosae, or Cucurbitaceae, he can assume the likelihood that some of his of algae not closely related to
knowledge
will
apply to other members of the same family,
A TEXTBOOK OF SYSTEMATIC BOTANY
10
although some verification will be necessary and differences in must be expected. On the other hand, if all plants with compound leaves were considered to be a family, this would give us an artificial group and no generalization would be safe except one regarding the leaves. Fortunately, in most of the spermatophytes phylogeny and convenience can be fairly well combined. Evolution as a Basis for Classification. The relationships of species or other groups are determined by the genetic lines running back from them to a common ancestor. Other things being equal, the shorter the genetic lines (in time) and the nearer the two species being considered are to the point where the two merge into a common ancestral line, the closer the relationship. However, if the two species are much alike, indicating that the two genetic lines have run nearly parallel, we call this condition detail
development, or parallel evolution, and these species are of as being more closely related than others that show greater differences and consequent divergence of phylogenetic lines that may have been much shorter. In considering evolution as a basis for classification, a student in any branch of biology has to make a decision among three alternatives: (1) to reject the hypothesis of evolution and with it parallel
commonly thought
the idea of true natural relationships, (2) to accept this hypothesis blindly on faith in the judgment of his instructor, or (&) to look into the evidence bearing on the subject. scientific
The
last
named
is
the
method.
EVIDENCES OF EVOLUTION of organic evolution should be made Evolution is believed to have produced all existing forms of plant and animal life from more ancient forms that were fewer in number and simpler in structure than those of the present day. It is not held that one group as it exists today came from another group as it exists today, but that similar groups had a common
At the outset the meaning
clear.
ancestor more or less like both.
A
great deal has been written in recent years on the evidences and also on the methods of its operation, concerning
of evolution
which some half-dozen plausible theories have been proposed. Space limits us here, however, to a brief outline of the best accepted evidence on which the belief in evolution is based.
EVOLUTION IN RELATION TO TAXONOMY
11
Geological Evidence. It is well known that the surface of the In the past slow but proearth is not smooth and unchanging. found changes have taken place. Land has been lifted out of the sea,
and mountains have been lowered by erosion
the materials
thus removed being finally deposited in the ocean as layers.
These layers have later been lifted to form new mountains, and the process has been and is being repeated again and again. Some of the strata of earth and rock that have thus been formed contain many fossils, the remains or prints of prehistoric plants and animals. The forms of life represented by these fossils give an important historical record of the kinds of living things that have existed on the earth during the past ages. If all kinds of plants and animals, higher and lower, had been created and established at the same time and place, we should expect the fossilbearing layers, both older and newer, to contain representatives of The older strata, those all of these, but such is not the case. formed before the Cambrian era (see frontispiece and table on pages 12-13), contain limestone, graphite, and fossils of primitive forms of life only, especially marine algae and invertebrate animals.
Strata not quite so old, those of the Paleozoic era, bear
complex invertebrates, lower vertebrates, seaweeds, Not before the Mesozoic era pteridophytes, and gymnosperms. were fossils of mammals and angiosperms produced, while the apes and man left no fossils below the younger layers of the Cenozoic fossils
of
era. It is generally accepted as a fact that the time from the Archeozoic era to the Cenozoic era covered hundreds of millions of years and that new species of plant and animal life kept appearThis leaves us ing on the earth throughout that extensive span.
with two alternatives: (1) that direct creation was repeated many times throughout all that vast period of time, up to the present, thus producing the hundreds of thousands of species now in existence and others that have become extinct, or (2) that the species that first came into existence were relatively few and simple and that they gave rise to newer and more complex ones by evolutionary processes. The latter seems the more plausible and is widely accepted.
Morphological and Anatomical Evidence. The members of different groups of animals and plants show striking similarities The spinal in fundamental structure but vary in lesser details.
12
A TEXTBOOK OF SYSTEMATIC BOTANY
EVOLUTION IN RELATION TO TAXONOMY O O
to
13
A TEXTBOOK OF SYSTEMATIC BOTANY
14
column in all vertebrates and the same number of limbs in mammals, birds, and reptiles suggest relationship through a common ancestor. In all the vertebrates, except the most primitive, there are four limbs, sometimes in a rudimentary, sometimes in a highly specialized, condition, and the skeleton of the arm and forefoot, for example, compares almost bone for bone with that in such superficially different structures as the walking organs of the
swimming flippers of the whale, the wings of the bat, and the grasping organs of man. In the spermatophytes every part of the sporophyte is some form of root, stem, or leaf; and every plant has all three of these bear, the
form and function. Given diploid. the general characteristics of the fibrovascular system, one can infer correctly in almost every case the number of cotyledons and The tissues of normal leaves show a the venation of the leaves. general similarity of plan with palisade cells above, in which respect they differ from cladophylls, which are leaf-like stems. The position of buds in the axils of leaves at nodes is likewise structures,
though they
may
differ greatly in
The chromosome number in these parts is always
uniform. This similarity of ground plan points to a development from ancestral forms by a process of evolution, which would be likely to modify existing structures rather than to create new ones.
Embryological Evidence. A special kind of anatomical evidence is found in the embryological development of higher animals.
The
ancients believed that, in general, living things and structure much like miniature
started with an appearance
growth and development being merely processes of enlargement of each individual organ. Scientific observation has adults,
is not usually the case. The fern, beginning with the germinating spore, first resembles a green alga. From This this develops a small thallus like those of the liverworts. form in mature with is the prothallium, turn, replaced by leafy,
revealed that such
which
The
all
are familiar.
frog in its metamorphosis goes from a one-celled state
through the tadpole stage, more like fish than amphibian, and changes to adult form by loss of tail and gills and development of
and
lungs. Insect larvae have no wings, not even rudimentary ones, and resemble worms, which they are often called. But these larvae,
legs
EVOLUTION IN RELATION TO TAXONOMY
15
by losing certain leg-like structures, taking on permanent legs and wings, and developing a definite segmentation, become in adult strikingly different creatures. is a term used to express a series of embryonic stages of individuals such as those just described. Phylogeny, on the
life
Ontogeny
other hand, expresses the evolutionary history of a race of beings from remote ancestors. HaeckeFs 'law of recapitulation/' translated into English, states that
'
Ontogeny is a brief repetition of phylogeny.' This law has been highly useful in tracing relationThe early stages of the advanced ships in animals and plants.
form and that of the simple form, presumably ancestral, are much alike, but the higher form continues its development farther and thus produces a complex individual. In a close examination of the higher Vestigial Structures. plants and animals one finds many structures wholly useless and
sometimes actually detrimental to the individual. Of what use to plants are scale-like leaves on rhizomes and tubers, stamens without anthers, and the antheridial cells of germinating pollen grains? Why should the legs of the horse include so many little bones, some of which by pressure against others become inflamed and cause splints and spavins? Why the easily infected vermi-
form appendix, the coccyx bones, and the scattered body hairs the
human
forms of
being?
life
Why
and so few
so
of
many
useless structures in higher As a result of direct in lower forms?
creation such structures would seem absurd.
Evolutionary development, however, would almost inevitably be accompanied by such vestiges of once useful organs. Great and varied environmental changes have taken place during the The changed conditions eras since life appeared on the earth. Some affected the existing plants and animals. profoundly but and were themselves to unable exterminated, species adjust for their fossil remains we should never know that they had existed. Other species became adaptedsto the new conditions by Some organs, such as bones, for structural modification. example, were lengthened, shortened, ootherwise modified, and in some cases were entirely lost. Useless structures became fitted to survive were those in best and the species encumbrances, which these superfluous parts were rapidly reduced and made unobtrusive or entirely lost. It sometimes happened, however, that another change of environment reestablished a need for the
A TEXTBOOK OF SYSTEMATIC BOTANY
16
organ in its original or equivalent form. If it was too far gone or too greatly modified, the victim perished, as doubtless happened in numerous instances, for by the law of irreversible evolution (see
page 28) animals and plants do not ordinarily go back to earlier Had the bodies of living things been so unstable that organs would quickly and entirely disappear with a brief change in the climate or the food supply, organic adaptation would have been oversensitive and caused destruction rather than protection. That myriad forms of life did survive profound environmental
states.
C
B
D
E
A, potato tuber with a scale-like leaf Vestigial structures in plants. at an 'eye.' C, Indianpipe, B, rhizome of peppermint with scale-like leaves. which is colorless and saprophytic and has scale-like loaves. D, staminode E and F, vestige of stamen in beard-tongue, in contrast with normal stamen. lodicule vestige of petal of wheat. (F, after Robbins.) FIG.
3.
changes sisted.
evidence t>f the tenacity with which unused organs perModification rather than destruction of organs appears
is
to have been the fortunate rule.
Furthermore, by this hypothemore frequent in the versatile, highly complex spermatophytes and vertebrates and more rare in
sis vestigial
structures would be
the simple, conservative, lower forms. Thus it can be seen that by a theory of evolution these vestigial or rudimentary structures can be explained naturally, while by a theory of direct creation they are inexplicable and inharmonious.
Recent Productions. has come
It
must not be supposed that evolution it began when the world was young,
to a standstill, that
EVOLUTION IN RELATION TO TAXONOMY
17
continued for a few million years, and then ceased to operate, leaving us with a great array of unchanging species. There can be no doubt that it has been continuous from the start, is still going on, and will continue into the indefinite future. That new species of animals and plants are forming all the time is a wellaccepted fact supported by observation and experiment. Variation from the parental characters appearing in offspring, followed by the survival of the fittest (a Darwinian principle), still goes on
and can be hastened experimentally by the geneticist. Of the offspring obtained by crossing related subspecies and species, many fail to reproduce or are poorly constituted to meet the conditions of their environment and soon disappear; some are in nature
and others, especially among plants, are fertile, surviving and multiplying; and their new combinations of inherited char-
sterile,
acteristics,
if
firmly established,
may
be
sufficient to constitute
them new species. The mutation theory of de Vries assumes that most evolutionary changes take place in this way. These processes go on among wild plants, and some of the resulting products are collected and given specific or varietal names. By the same processes other products are made by plant Varieties of corn, fruits, and vegetables, wonderful breeders. all these and many of dogs, pigeons, and goldfish breeds flowers, more existing forms of life we know have actually come from ancestry that was very different. That we now call these different cultivated and domestic forms varieties rather than species is of little significance, for there is no doubt that many of them, if found wild, would unhesitatingly be given different specific names. The fact must not be overlooked that these recent productions have been made in a relatively brief time. Compared with the duration of life on the earth, the existence of civilized man has been as a day is to a century. One could not expect, therefore, that a considerable number of new species would become estab-
lished in so brief a span.
ACCEPTANCE OF THE DOCTRINE OF EVOLUTION The popular conception that Charles Darwin was the
first
to suggest the origin of species through a modification of previDuring the first half of the ously existing species is an error.
A TEXTBOOK OF SYSTEMATIC BOTANY
18
nineteenth century at least a score of writers, 1 including both scientific men and theologians, gave some expression to this idea, mostly in the form of brief comments incidental to a discussion of
The tendency of these early writers was to subject. express their belief, sometimes supported by evidence, that certain species had originated by successive changes in ancestral some other
without claiming that such a method of origin was universal few even went so far as to include man among or even general. the products of evolution, and it seems surprising that they
lines
A
remained unchallenged.
FIG.
4.
tion of the
The Darwin-Wallace medal given by the Linnaean Society in recogniwork of these two great pioneers in the study of organic evolution.
(Courtesy of Popular Science Monthly.)
In 1858, Alfred Russel Wallace, a young English naturalist, sent to his older and better known countryman, Charles Darwin,
a hastily prepared manuscript setting forth his views on the origin of species through variation and natural selection, closely similar to the unpublished conclusions of Darwin but reached independently. Upon the insistence of his friends Darwin pre2 pared a summary of his own work, which was published jointly with the paper submitted by Wallace. This was followed a year '
by Darwin's book in two volumes on the Origin of Species/' which was the product of some 20 years of study. It is a matter of history that the theory of evolution, when first set forth by
later

Most of these
are mentioned in the Historical Sketch of Darwin's 'Origin
of Species.' 2
DARWIN, C. and A. WALLACE, On the tendency of species to form varieand on the perpetuation of varieties and species by natural means of f
ties;
selection, Jour. Linn. Soc.
London, 3
:
53, 1858.
EVOLUTION IN RELATION TO TAXONOMY Darwin and his associates, was seriously challenged because seemed so revolutionary. At the present time, however, it given the same recognition as that accorded to other principles all fields
of science.
Its adoption
course
it
it is
in
has revolutionized the classiis most needed now is
and animals, and what more information as to the methods of fication of plants
19
has followed, in order that we
its
may
operation and the
complete our knowl-
edge of phylogenetic taxonomy.
THE MECHANISM OF EVOLUTION The fact that organic evolution takes place is generally accepted, but the explanation as to what causes it to go on has been difficult to ascertain. The endeavor to do so has involved numerous researches in genetics, cytology, and ecology, and yet our knowledge on the subject is far from complete. While it is generally believed that the rate at which evolution operates has varied appreciably during different periods of geologic time, it is also thought that in terms of a human lifetime it has been very slow.
In the evolutionary process many patterns and materials have been used, most of which have been discarded. The present life on the earth is the product of this long process of trying, sorting, The experimental biologist interested selecting, and discarding. in this subject is able to study only the relatively elemental steps in the process, such as those that take place within the species. On rarest occasions he has been able to reproduce artificially an existent natural species, but the genetic relationships of genera, families,
and higher groups at present are closed to experimental
Their evolution has gone so far that it is doubtless impossible to repeat the steps with the living forms that
investigation.
now
remain on the earth. Variation and Natural Selection.
Darwin recognized two great principles of evolution, vaiiation of the offspring from the parental characters and survival of the fittest by natuial selection, but he did not fully understand the explanation of either. Variation is the active agency that develops new forms upon which evolution may build; natural selection is ever operative upon this variation, eliminating many forms and perpetuating, in general, those best fitted to survive in that environment in which they find themselves.
A TEXTBOOK OF SYSTEMATIC BOTANY
20
The Kinds
of Natural Variation.
heritable
sorts,
and
Variation in plants is of two Failure to differentiate
nonheritable.
between these has been a source of some confusion in taxThe heritable variations, which are transmitted from parent to offspring, are the only kind that have significance in clearly
onomy.
The nonheritable
evolution. life
variations are acquired during the
of the individual as direct effects of the environment.
These
are temporary and reversible and consequently of no significance to either evolution 01 taxonomy, but it is not always possible to
them from
heritable variations without performing an Undoubtedly, new specific names have been given to some of these, and they can be found in herbaria so named. Variation is common to all plants whether they reproduce asexIt is to be expected, of course, that there is ually or sexually. relatively much less variation among those forms that depend upon vegetative reproduction, whether it be by simple fission, as
distinguish
experiment.
in the lowest plants, or by aerial bulblets, layering, or development of seed without fertilization (apomixis), as in the higher
plants.
Self-pollinated forms are likewise less variable than those
that must be cross-pollinated. The genetic variations among plants of a given kind in a single population are often trivial in appearance and in themselves of no
evolutionary or taxonomic significance. When plants of all the populations of a common hereditary pattern in an area are con-
and compared with those of a somefound growing in another climatic region,
sidered together, however,
what
different pattern
then the evolutionally significant climatic races or subspecies of a single species are disclosed. The hereditary patterns of different species are ordinarily less similar than those of the climatic races of one species, but the degree of morphological difference The genetic relationship alone is not the final mark of a species. is a sounder criterion of origin than is morphology but more difficult to
The
determine.
species of a genus
have a number
mon that mark them as a group
distinct
of characteristics in
from other groups.
com-
The
explanation for this lies in their common evolutionary origin. Experiments show that in most genera many species are still In closely enough related to be able to hybridize to some extent. this
intermix their hereditary materials slightly and When one group is no longer characters in common.
way they
retain
many
EVOLUTION IN RELATION TO TAXONOMY
21
able to hybridize with others in the same genus, it has attained the genetic mechanism for becoming an independent genus. In
most
cases,
required for
however, perhaps it
many thousands
of years
are
to differ sufficiently to be considered a distinct
genus. It
has been noted that some species, e.g., the maidenhair tree, biloba, a gymnosperm, and sassafras, Sassafras ariifoiium
Ginkgo
y
a small deciduous tree
common in the eastern United States, have
not undergone any important variation for millions of years, while
some genera, e.g., Oenothera, Senecio, Datura, Rubus, Crepis, and Carex, and in some cultivated plants, including barley and maize, variations are very common. Obviously, such groups lend themselves readily to the work of the plant breeder and the
in
Viola,
Anjllusgeneticist in their endeavor to produce new varieties. tration is found in the genus Rubus, which includes blackberries, etc., from which the newer loganberries, youngand boysen berries have been produced.
raspberries, berries,
all stages in the evolutionary process are found in nature, not surprising that there is some disagreement as to what rank to accord different groups. Because the morphological gaps become greater as the rank of the group is increased, most confusion surrounds the subdivisions of species, and the delimitation of Much less is connected with the separation species themselves.
Since
it is
of genera, and there is considerable uniformity of opinion as to the delimitation of families.
The Mechanism
of Variation.
heritable variations
generation rightly
who
and
falls
A
study of the many kinds of from generation to
their transmission
within the
field of genetics.
However, the
trying to classify the end products of evolution from the viewpoint of phylogeny also has an interest in the mech-
taxonomist
is
anism of evolution. As each individual is usually the product of the union of two sex cells, one contributed by the male and the other by the female parent, all heritable variations must have come through these. Variation arises in several ways. In the first place, it is obvious two unlike individuals cannot be identical with both of them. Its appearance will largely depend upon the
that the offspring of
the hereditary substances received from each parent. Consequently, the offspring may look a little different from either parent. In general, the more unlike the parents
interaction
of
A TEXTBOOK OF SYSTEMATIC
22 are,
BOTANY
the greater the variations within the offspring are apt
to be.
Secondly, the hereditary substance itself is subject to occasional change. While this is usually first noted in the products of reproduction, it may have been initiated in the 'resting' nuclei prior to reproduction. This is apt to give rise to new characters not found in either parent. Such spontaneous origin of new variation is known as mutation. At one time mitosis and meiosis were to follow a definite pattern, but we know now supposed always that such is not always the case, that even the chromosome numbers may change. Such abnormalities may result in partial or
complete
sterility in
the offspring, or in morphological changes.
Both hybridization and mutation are important building stones in the evolutionary process. Different kinds of mutation occur, all of which cause variation. Most of them take place in the structures within the nucleus that The carry the hereditary substances, viz., the chromosomes.
number of chromosomes may change, or their parts may become Changes in number rearranged, or their contents may mutate. are detectable under the microscope and rearrangements often are; but the changes in content, which are usually slight, else death results, are invisible except as the effects can be observed in
the offspring. or
When cross-pollination takes place, whether it goes on in nature is carried on by man, various results may follow, depending on
the character of the parents. Because of genetic barriers, i.e., incompatibility of the gametes, shortness of the pollen tube, etc., If fertilization may not take place and no seeds will be formed. it or or is be lacking offspring produced, may partially so, sterile, in vigor and unable to cope with its environment. With proper chromatin combinations there may be no genetic barriers and vigorous offspring may be produced, which, if isolated in a suitable environment, may form new lines that will in time develop into new subspecies or even new species. Some causes of mutation are known, but many others remain undiscovered as yet. Some mutations are caused by environmental factors such as temperature changes, aging the seed, and certain radiations such as rays, all of which may affect the chromosomes and induce variation in the offspring. Other mutations are induced by genetic causes such as the hybridization of widely unlike forms.
X
EVOLUTION IN RELATION TO TAXONOMY
23
The fundamental
unit in heredity is the gene, the element of material upon which some morphological or physiohereditary of the condition organism depends. Very many genes are logical
aligned along each chromosome. A mutation in one gene is seldom very significant to the organism, but many such mutations
accumulated over a period of time composition of a given form.
may
significantly alter the
After years of research there is still a difference of opinion geneticists as to whether new species originate more com-
among
monly from pre-existing ones by sudden major mutations or by the gradual accumulation of many minor heritable differences, such as gene mutations.
The Importance
of Isolation.
The innumerable
variations
that arise through mutation and are recombined in various patterns through hybridization are continually subjected to the New forms are unable to exist for forces of natural selection. long in competition with the old unless their identities are maintained
by
genetic
or
environmental isolation of some
sort.
Genetic isolation is brought about by internal barriers to the successful continued crossing with the pre-existing forms. Such barriers include incompatibility of the sex cells, different dates of flowering,
etc.
Environmental isolation
is
largely spatial or
geographic.
Evolutionary Processes. As a rule, the more closely related that plants are to each other, the more likely they are to be capaPlants from different families cannot ble of successful crossing. ever be crossed, and those of different genera only rarely. It is often possible to cross species of the same genus, but this may be prevented by genetic barriers such as differences in the number or composition of the chromosomes or in the character or positions of the genes. Subdivisions of the species, ?.e., related subspecies, varieties, races, etc., ordinarily cross without difficulty. Hybrids between two plants of the same species may show considerable morphological variation, but they are ordinarily fully In this respect they differ markedly from hybrids
fertile.
between different
species,
which are at
least partially sterile, pro-
ducing inferior offspring. The hybrids between genera, in the few instances in which they are obtained, prove entirely sterile. The multitude of variations produced in nature are subjected to selection by the environment, and the unfit are eliminated, New forms become well established only often very promptly.
A TEXTBOOK OF SYSTEMATIC BOTANY
24
when by heredity they are in harmony, with their environment. As climates change through periods of time, new environmental niches may become available for occupation by suitable forms, and the old habitats become much modified. If the species is to persist, one of two things must happen: either it migrates into habitats
still
favorable to
cient to permit
it
it,
to develop
or its capacity for variation
is suffi-
new forms in harmony with the chang-
Extinction has been the lot of innumerable ing environment. forms that have faced environmental change with too little genetic capacity for variation. Even though there are now hundreds of thousands of species of plants and of animals, there are not nearly so many as might be
expected
if
one considers the frequency with which mutation and
hybridization take place and the millions of years that evolution has been going on. Researches in paleontology have shown that
and animals that were once well estabbecame extinct because of environmental changes, increase of enemies, etc., and undoubtedly there have been innumerable hybrids, mutants, and variants that did not persist long enough ta produce fossils and so were lost entirely.
many
species of plants
lished
on the earth
later
ACCOMPLISHMENTS OF EVOLUTION The millions of individual plants and animals covering the earth and constituting thousands of species are looked upon as so many products of evolutionary development. What the first form of life was, whether it originated at a single point or several, and whether or not plants and animals had a common ancestry are questions that cannot be answered now. Every species of shows a now on the earth animal and complexity of strucplant ture far beyond what must have been possessed by its remotest It is doubtful if that ancestor was even a well-organancestor. ized
cell.
Much
evidence points to the conclusion that during the vast eras of organic development periods of accelerated progress took
Conspicuous in the plant kingdom was first the production of chlorophyll, and millions of years later the structural adaptation to a terrestrial enviroment and the advent of an alternation of generations of the progressive character found in
place.
bryophytes and pteridophytes. Prior to these last two epochmaking events changes among the marine plants appear to have'
EVOLUTION IN RELATION TO TAXONOMY been relatively slow.
35
.With a land-and-air environment and a
progressive sporophyte alternating with a waning gametophyte in each life cycle, increase in complexity appears to have taken
place
by leaps and bounds.
It is
a significant fact that while some forms progressed rapidly
Had
others were relatively stable.
all
changed equally, we
should have no lower plants and animals now.
have changed more or
less
from
their ancestral
Doubtless all forms but some
This fact is a great help in the study of phylogrelatively little. eny, for the progressively higher forms may be compared to a series of pictures of evolution, taken as it marched past.
PROGRESSIVE AND REGRESSIVE DEVELOPMENT As a matter
human
of convenience
standards
we say
gressed or degenerated.
and may be misleading
and
in accord with our
narrow
that phylogenetic lines have either proThese terms must be used with caution
if
the situations to which they apply are
not closely analyzed. Indications of
Upward or progressive an in qualities beneficial increase implies development generally to the race. Upward Development.
In is usually looked upon as progressive. and animals than are the lower the larger general, higher plants Tall plants may be ones, though there are numerous exceptions. Increase in size
able to reach the light where shorter ones would be deprived of it. Large animals may be able to overcome smaller ones in combat,
however, may become a hindrance, especially among animals, where food is scarce or where the ground has become too soft for locomotion. In all likelihood this aided in the extinction of certain huge prehistoric other conditions being equal.
reptiles
and mammals.
The
Size,
fact that trees are
waning while
herbaceous plants are increasing suggests a condition analogous to It may be that as conthat found in the animal kingdom. ditions are now on the earth herbaceous plants are better suited to survive than
woody
plants.
Increase in specialization
advancement. root hairs,
and
is
a more certain indication of
The developments
of heterospory, of stomata, of of palisade tissue in leaves, to take the place of less
differentiated structures, are familiar examples.
In the lower
A TEXTBOOK OF SYSTEMATIC BOTANY
26
plants one cell or a simple filament may perform the functions of of these but do it less efficiently. Organs specialized for ' division of labor ' are characteristic of both higher animals and
all
higher plants.
Quite clearly there may also be danger in specialization, either because the specialized organ becomes an encumbrance, or because of the fact that with specialization of a given structure to do certain work there comes to be a lessened ability on the part of other structures to do equivalent work.
When
conditions are
right for the specialized organs to function effectively, the plant prospers, but with altered conditions more conservative struc-
tures
may
save the race.
Two
examples
will
make
this clear.
conditions were favorable for insectivorous plants to obtain most of their nourishment from their prey and other food were (1)
If
scarce, specialization of 'fly traps' with the inevitable reduction of other organs of nutrition would be advantageous; but should
the supply of insects
fail,
the more conservative ancestral forms
that could obtain their food materials directly from soil and air would be more likely to survive. (2) Xerophytic structures are well adapted to arid conditions, but a xerophyte in a
would be worse
off
swamp
than a mesophyte.
It is now agreed that the plants and animals with organs highly specialized in one direction are not usually the ones from which
These greatly specialized groups more higher groups evolved. It is doubtful often form side branches to the main genetic stem. whether Pilobolus, Hydrodictyon, Marchantia, or the specialized insectivorous plants have given rise to any important group or, indeed, if they ever will. Specialization of animals has far exceeded that of plants, particularly in the various methods of locomotion and in the
marvelous development of the nervous system and special senses. Correspondingly, they appear to have suffered even more than plants from excessive specialization in directions that were an obstacle under changed environmental conditions. Forms of Degeneracy. It is in a study of so-called degeneracy It is usual to that we need to think our way most carefully. once or of functions of structures loss useful, or any regard any increased tendency to be dependent on other forms of life, as degeneracy. The question is largely one of definition and interpretation.
The conspicuous example
of
degeneracy in the plant
EVOLUTION IN RELATION TO TAXONOMY kingdom
is loss of
It is
chlorophyll.
probable that the
27 first liv-
ing things on the earth had no chlorophyll and that its acquisition was one of the greatest events in the history of the organic world. The ancestors of the fungi appear to have acquired it, but in their change to fungi they lost it. So also with the Indianpipe and a few other angiosperms. If planted in an environment of abundant and suitable organic matter, with little light, these plants thrive better than their chlorophyll-bearing relatives; but if stranded in an inorganic environment they perish. It is a wellestablished fact that plants that have completely lost their chlorophyll and the plastids containing it never regain them. Such plants represent independent species that have degenerated into saprophytes.
Parasitism
another form of degeneracy
is
common among
Strict or obligate parasites thrive when plants and animals. associated with certain hosts but not elsewhere. Such obligate
Most parasites, especially fungi, parasites are, however, rare. retain saprophytic power, which they use in times of necessity, and many
them
live a saprophytic life more commonly than a Saprophytic fungi often thrive better than algae growing in the same region, and in acquiring a saprophytic habit they have gained more than they have lost. It is not safe to class all loss of parts as degeneracy, for sometimes this loss is a form of specialization. Several examples may be cited. (1) In pteridophytes a megaspore mother cell produces four functional megaspores, but in most spermatophytes it forms four cells that are potential megaspores, one of which develops at
parasitic
of
life.
the expense of the others, which fail to enlarge and disappear. (2) Bisexuality in angiosperms is looked upon as a primitive condition, while unisexuality,
carpels from the (apetaly), in
flowers,
by the evolutionary more advanced.
is
loss of (3)
stamens or
Loss of petals
considered an indication of ' the term 'regressive development is Probably
some
cases at least,
is
advancement. more fitting than 'degeneracy.'
When
it is
remembered that
all vestigial
structures (see page
15) are products of degeneracy, that they are usually the result of adaptation to a changed environment, and that they are
especially prevalent in the higher forms of life, we see that it is necessary to give a liberal interpretation to what is commonly called degeneracy.
A TEXTBOOK OF SYSTEMATIC BOTANY
28
Evolution Is Irreversible. In 1892, Louis Dolle, a Belgian paleontologist, put into concrete form a principle that had been vaguely felt by others. As restated in 1901, it is as follows: 'An
organism never exactly renews a previous condition, even if it an environment identical with one through whicR it has passed. But, by virtue of the indestructibility of the past, it always retains some trace of the intermediate stages which ' This 'law of irreversible evolution' has many it has tra versed. When organisms havo applications in both botany and zoology. become profoundly changed through adaptation to environment and then have been resubmitted to the earlier conditions, they have not gone back to ancestral types but ha e become adapted through new modifications. We hold that at one time all plants were aquatic, that some of their progeny developed terrestrial
finds itself placed in
habits and structures, and that some of the progeny of these terrestrial plants became aquatic again; but in doing so they
become marine algae like their ancestors. few examples of apparent reversibility, however, may be found in certain organs among flowering plants. There is little doubt that primitive evergreens gave rise to deciduous plants, some of which in turn became evergreen, as illustrated by the certainly did not
A
Oregongrape, and live oak. Apparently quite frequently, plants with one leaf at a node gave rise to others with two leaves at a node, although in all probability all came from ancestors that
holly,
were uniform with respect to the arrangement of leaves on the stem. Broad leaves have given way to narrow ones and vice versa. Furthermore, herbaceous plants have arisen from woody in a few cases they have given rise to woody forms and forms, It is true that the newer product is not an exact reproagain. duction of the ancestral one with respect to the quality in question, but, nevertheless, the apparent reversal may mislead the student of evolutionary tendencies. It is quite possible that minor changes, especially those of physiology, require some time to become permanently established, and that before that time is complete, the plants, in adaptation to a change in the environmental conditions, may In the main the law holds true, revert to an original condition. however, and is a great guiding principle. It may seem to con' with the belief in reversion to type,' but so little is known
flict
of the underlying principles of this so-called reversion (except as
EVOLUTION IN RELATION TO TAXONOMY an expression
of recessive
Mendelian characters or recurrence of
primitive factorial combinations) that
it
does not weigh heavily
against Dolle's law. In the further development of the topic of will
chapters, phylogenetic arrangements possible, but since the scope of the book
taxonomy
be followed as
in later
much
as
restricted chiefly to the problems of relationships is
many perplexing the lower plants will receive only incidental consideration.
Spermatophyta,
among
29
CHAPTER
II
METHODS USED
IN THE IDENTIFICATION OF FLOWERING PLANTS
When
one collects flowering plants and wishes to determine among the thousands to 'which names have been
their species
magnitude of the problem might seem to make it hopeThe methods, however, have been worked out so well that
given, the less.
the average college student, with a background of one course in general botany, can learn to perform the task rather easily,
except for a few kinds that belong to the more difficult large genera, such as Astragalus, Poa, Carex, Pentstemon, and Senecio, and many species in these genera are not difficult to identify. No Short-cut Method. The greatest difficulty is had by the amateur who does not know the morphological terms by which
There is great demand for a small, handy plants are described. book with colored illustrations and nontechnical descriptions from which any flowering plant can be easily and quickly identified by those who have made no study of botany. Unfortunately, such a book could not possibly be made for the number of species is so great that it would have to be very large, its cost would be prohibitive, and the amount of time required to sort through all of the descriptions and illustrations for the plant in question would be discouraging. Furthermore, some species are so much alike in general appearance that even colored photographs would fail to ;
bring out distinctions that are based on small or concealed parts if the descriptions were written in common terms, these ;
and
distinctions could not be made.
The
best attempts in this line are books and pamphlets that picture and describe some of the more conspicuous and interest-
ing plants of a limited region and omit the others.
They
are use-
but far from satisfactory. Names. Popular books on plants often give both the common and the scientific names, but while those species that have been studied have all been given scientific names, thousands have never ful
30
IDENTIFICATION OF FLOWERING PLANTS
common names
been given
that distinguish them from others in
The genera
the same genus.
31
Astragalus, Carex, Lupinus, Rosa,
and Poa, for example, all contain many species which do not have common names that distinguish them one from another. The Securing of Suitable Specimens. The difference between the ease of identification of poor specimens and of good ones is very great, and it is well worth while to collect and preserve careAs a rule, fresh specimens are more easily studied than fully. If the student is required to hand in a small dried or wilted ones. herbarium as a part of his assignment, he should by all means press some of his specimens as quickly as possible in a field press, if ono is available, and keep others fresh in a covered pail or a vasculum for detailed study and identification. Small portions of plants, bearing flowers and a few of the upper leaves only, are generally Fruits and seeds may or may not be required. unsatisfactory. Too often collectors carelessly fail to provide the proper equipment for obtaining good specimens, with the result that time is wasted in trying to work with wilted, dried, or otherwise poor Senecio,
More
material.
page
detailed directions for collecting are given on
46.
While the gross morphology for Studying Plants. can be observed easily, certain line details, such as the
Implements of plants
The internal structure of the ovary, call for careful dissection. most useful implements arc found in a regular biology dissecting but a sharp scalpel or knife, a pair of dissecting needles (which can be made by pushing the heads of coarse sewing needles The into the ends of sticks), and a safety-razor blade will suffice.
set,
razor blade is extremely important, for it is often necessary to cut the ovary in longitudinal or cross section to study the ovules and their attachment, and a clean cut with a sharp instrument is best.
A simple hand lens with a magnificalens also is necessary. tion of five to ten diameters is generally used by beginners, but a binocular of relatively low power is a great help, especially in work
A
with grasses.
Manuals of Botany. Many books, large and small, have been written on the plants of different parts of the country. Some of these, like Gray's 'New Manual of Botany,' cover very large These botanical others are for very limited regions. ' a on few aspects of manuals' or floras' concentrate only
areas; '
botany
7
generally
names and descriptions of families, genera, and
32
A TEXTBOOK OF SYSTEMATIC BOTANY
species found in the region, with keys for identification and a glossary of technical terms. Some are illustrated, some are not.
They are technical books and are not to be confused with popular books on flowers, since they are for the use of people interested in botany for professional or serious amateur work. The amateur botanist who has not made a detailed study of floral structure, who has not learned the terminology of plant parts, who has not the patience to make fine distinctions, or whose interest is limited to plants with showy flowers is likely to be discouraged in his first attempts to use technical manuals but not a few amateurs have overcome these difficulties by hard work and have become quite proficient in identification. For the use of college students these manuals, more or less local ;
in their range and consequently limited in their content, are of inestimable value, for they provide the most convenient means for
the identification of the plants that they are studying.
KEYS FOR IDENTIFICATION For the beginning botanist analytical keys are almost indispenand even the professional often makes use of them. How Botanical Keys Are Made. Analytical keys have been used for several generations in books for the identification of The plants, and all modern manuals of botany contain them. principle involved is that of finding contrasting characters and using them for dividing the group being studied into two or more For example, the plant in question and some others branches. may have irregular flowers while some of the group to which they belong have regular flowers. In this way a part of the group is eliminated from the range of possibilities, thus narrowing the problem. Then the key may show that some have simple leaves and others compound leaves and that some are pubescent while
sable,
By contrasting a sufficient number of chartime each acters, eliminating some members of the group, the number of possibilities is finally reduced to one the name sought others are glabrous.
for.
In identifying angiosperms it is common practice to have the key first indicate whether the specimen in question is a dicotyledon or a monocotyledon and then by a contrasting seiies of characters run it down to its family. Another key will similarly direct the search to the genus and a final one to the species. A
IDENTIFICATION OF FLOWERING PLANTS
33
natural procedure would be to have keys from the classes to the orders and others from the orders to the families, but most of the manuals omit oiders from their keys.
The Structure of Keys. Several different types of key have been devised for plant identification, two of which are especially important. Both are distinguished by the method of printing them in the book or other publication where they are used. The indented key is the one most used in manuals for the of spermatophytes. In this type of key the each character is indented a fixed distance from the left-hand margin of the page, the contrasting characters having the same indentation. As progress is made in running a plant the the lines are more and more indented for each key, through or of pair group characters, so that in a lai ge key the lines become
identification
description of
very short. In the bracket or parallel type of key two or more contrasting characters are described in consecutive lines of the page so that they are easily compared. At the end of each line is either the name sought for or a number that, repeated at the beginning of a lower line, carries the search to another contrasting pair or set of characters. This process is continued to the end of the key. For very large keys the biacket form is more suitable than the indented key. 1 The same material arranged in the form of indented keys and of bracketed keys of small size is given for comparison.
INDENTED KEY TO THE FAMILY POMACEAE Ripe carpels papery or leathery Leaves pinnate Leaves simple, entire, toothed, or lobed
Sorbus
Cavities of the ovary (carpels) as many as the styles Flesh of the pome with grit cells
Flesh of the
pome without
Pyrus
grit cells
Mains
Cymes simple trees Cymes compound low shrubs ;
;
Cavities of the ovary becoming twice as 1
2
many
Aronia as the styles Amelanchiet
' For a very large bracket key see Gilbert M. Smith, Fresh-water Algae United States,' 1st ed., pp. 626-644, McGraw-Hill Book Company,
of the
Inc., 1933.
' BRITTON, N. L., and ADDISON BROWN, Illustrated Flora of the Northern Vol. States and Canada,' 1st ed., II, p. 238, Charles Scribner's Sons, 1897. 2
A TEXTBOOK OF SYSTEMATIC BOTANY
34
Ripe carpels bony Ovule 1 in each carpel, or if 2, dissimilar Ovules 2 in each carpel, alike
CrataeguS Cotoneaster
BRACKET OR PARALLEL KEY TO THE FAMILY POMACEAE Ripe carpels papery or leathery Ripe carpels bony 2. Leaves pinnate 2. Leaves simple, entire, toothed, or lobed
1. 1.
2 C
Sorbus 3
4 Cavities of the ovary (carpels) as many as the styles Cavities of the ovary becoming twice as many as the stylos Amelanchiei 4. Flesh of the pome with grit cells Pyrus
3.
3.
Flesh of the pome without grit Cymes simple; trees Cymes compound; low shrubs 4.
5.
5.
6. 6.
5
cells
Malus
.
.
.
Ovule 1 in each carpel, or if 2, dissimilar Ovules 2 in each carpel, alike
Aronia
.
Crataegus Cotoneaster
.
.
.
.
.
INDENTED KEY TO THE FAMILY LEGUMINOSAE Stamens 10, wholly Leaves digitately
1
distinct 3-foliolate; flowers yellow
Thermopsis Leaves odd-pinnate flowers white Sophora Stamens (some or all) united by their filaments, at least at base .. Lupinus Anthers 2 forms stamens monadelphous Anthers all alike, renifbrm Leaves odd-pinnate, without tendrils Pod not a loment, 2-valved or indehiscent Foliage not glandular-dotted .
;
;
Digitately 3-foliolate or rarely 5-foliolate Leaflets entire
.
.
.
Lotus
Leaflets serrulate or denticulate
Flowers in racemes Flowers capitate or in short loose spikes .. Pods curved or coiled. ..
.
.
Melilotus
.
Medicago
.
Trifolium straight, membranous Pinnately 5- or more-foliolate (rarely simple or 3-foliolate in Astragalus)
Pods
.
Shrubs
Robinia
Herbs, or rarely with ligneous base .. Keel of the corolla blunt Keel of the corolla acute .
Astragalus Aragallus
Foliage glandular-dotted
Pod with hooked Pod not prickly Shrubs 1
COULTER, JOHN M., and AVEN NELSON, American Book Company, 1937.
p. 270,
Glycyrrhiza
prickles
Amorpha
'New Manual
of
Botany,'
IDENTIFICATION OF FLOWERING PLANTS
35
Herbs, or merely with ligneous base
Leaves digitately 3-5-f oliolate Leaves pinnately 5-many-foliolate Stamens 10
Stamens 5
Psoralea
Parosela
Petalostemon
Pod a loment, with reticulated indehiscent joints Leaves even-pinnate, terminated by a tendril or bristle Style slender, with a tuft of hair near the apex Style flattened, hairy on the inner side
Hedysarum Vicia
Lathyrus
Some indented
keys, especially very large ones, have numbers, other or characters at the left to make the key easletters, stars, This is made necessary by the number of different ier to follow.
indentations required, which may even result in one of a pair appearing on one page of the book and its mate on a later page.
BRACKET OR PARALLEL KEY TO THE FAMILY LEGUMINOSAE 1. 1.
Stamens 10, wholly distinct Stamens (some or all) united by
2 their filaments, at least at
base 3 Leaves digitately 3-f oliolate; flowers yellow Thermopsis 2. Leaves odd-pinnate; flowers white Sophora Anthers of 2 forms; stamens monadelphous Lupinus 4 Anthers all alike, reniform .5 4. Leaves odd-pinnate, without tendrils 4. Leaves even-pinnate, terminated by a tendril or .
2.
3. 3.
.
bristle 5. 5.
17
,
Pod a loment, with reticulated indehiscent Pod not a loment, 2-valved or indehiscent
joints
Hedysarum 6
Foliage not glandular-dotted
6.
7
13
6.
7.
Foliage glandular-dotted Digitately 3-f oliolate or rarely 5-f oliolate
7.
Pinnately 5- or more-foliolate (rarely simple or 3-foliolate in
9. 9.
11.
11.
13.
8 11
Astragalus)
8.
Leaflets entire
8.
Leaflets serrulate or denticulate
Flowers in racemes Flowers capitate or in short loose spikes 10. Pods curved or coiled 10. Pods straight, membranous Shrubs Herbs, or rarely with ligneous base 12. Keel of the corolla blunt 12. Keel of the corolla acute Pod with hooked prickles
Lotus 9
Melilotus 10
Medicago Trifolium
Robinia 12
Astragalus Aragallus
Glycyrrhiza
A TEXTBOOK OF SYSTEMATIC BOTANY
36 13.
Pod not prickly 14.
15.
15.
17. 17.
14
Shrubs
Amorpha
14. Herbs, or merely with ligneous base Leaves digitately 3-5-foliolato Leaves pinnately 5-many-f olio late 16. Stamens 10 16. Stamens 5 Styles slender, with a tuft of hair near the apex Style flattened, hairy on the inner side
15
Psoralea 16
Parosela
Petalostemon Vicia
Lathyrus
Keying Large versus Small Groups. The making and using of a key for a small group is obviously much easier than for a large group. A key to all the families of angiosperms in the United States would have to make use of many distinctions, some of them based on rather fine points, but a key that included only the families of a small area would call for the use of only a few easily determined characters.
TROUBLESOME VARIATIONS AND EXCEPTIONS Both in the use of keys and some allowance has to be made in individuals, or
even
in comparing with descriptions, for exceptions and for variations in the parts of an individual.
Intergrading Characters.
To
contrast the characters, as
done in keys, they need to be clear-cut and
distinct.
If
is
they
often perplexed to know where the line which branch to follow in the key. If one
intergrade, the student
is
should be drawn and has to contrast blue flowers with red flowers and those of his specimen are purple, or if the key contrasts pubescent leaves with glabrous leaves and his specimen bears a few scattered hairs, he is in doubt which branch of the key his specimen fits best. Some keys are much better constructed than others in this respect and avoid intergrading characters. When there is doubt which branch of a key to follow, it often becomes necessary to follow one until the correct goal is reached or until there is evidence that one is working in the wrong section of the key, and then, if necessary, to go back and follow the other. Theoretically this should never
be necessary, but practically it sometimes is. Exceptions to Rules. Some individuals and some species do not fit in all respects the descriptions laid down for the groups in which they are found. Some hawthorn shrubs bear few or no thorns. Lupines are generally blue-flowered, but some are white or nearly so; in fact, albino flowers are not uncommon in various species that are
commonly blue
or purple.
Figure 94, page 266,
IDENTIFICATION OF FLOWERING PLANTS
37
shows leaves from the same individual plant of mountain maple varying from simple and nearly entire to compound. In some species, e.g., Thlaspi arvense, the lower leaves are petiolate and the upper ones are sessile and clasping. Great variation can be found in the size of flowers in some species. Species with most members erect may have some individuals that are prostrate or nearly so, and vice versa. The habitat in which the plants are
morphology considerably, especially the be remembered, however, that environmental conditions, such as moisture and light, affect the leaves and stems much more than the flowers. Considerable experience, judgment, and patience are required to know how much deviation may be allowed from the key or the growing size.
may
affect their
It will
description.
Fruits and Seeds. A good, full description of a group such as a genus or a family will include the fruits and perhaps also the seeds. However, it is often annoying to find such characters in keys, because the specimen being identified, although it has good This flowers, may be too young to have well-developed fruits. met with is most classes that run by commonly difficulty during the second semester or the spring quarter of the college year. Fortunately, a careful study of the ovaries will enable the student to anticipate some of the fruit and seed characters, such as the
chambers and seeds and where the seeds are It has been found especially the placentation. attached, i.e., difficult to avoid using fruit characters in making generic keys to
number
of seed
certain families, notably Cruciferae
and Umbelliferae.
Comparing with Descriptions. A serious mistake commonly made by beginners is to assume when a category is reached e.g., family or genus that there has been no mistake in observation or An interpretation and that the correct group has been found. error may lead to endless trouble, and the student should make it an invariable rule to compare the specimen with the description of the group before he starts to run it down to a lower category. Not infrequently he will thus find that the plant does not fit the description in one or more important characters because he has made an error and placed the plant in the wrong group.
PORTRAYAL OF PLANTS AND PLANT GROUPS In order to discuss individual plants, species, and larger group*, with other people, it is necessary to have effective methods of de-
A TEXTBOOK OF SYSTEMATIC BOTANY
38
scribing them, for names are insufficient except among people who While showing are very familiar with what the names stand for.
the plants under consideration is most effective, it is often impracticable because they are not available at the time. Several
methods are in common use useful but none perfect.
for describing plants, all of
which are
Descriptions in Common Terms. It is surprising how difficult to describe a plant in simple language so that another person
it is
In fact, it may be said that, it will recognize it. except for a few kinds of plants with very unusual characters, such as pines, oaks bearing acorns, insect-catching plants, and water-
familiar with
attempts to identify plants by such descriptions usually fail. Descriptions in Technical Terms. The use of technical terms ensures brevity, for in common language a whole sentence or more may be required to state what is covered by a single technical word such as ' spadix ' or ' ament.' Technical descriptions have lilies,
all named species and for the higher categories. botanist reading such a description can often visualize the appearance of the plants in question sufficiently to identify them.
been written for
A
If
the description
is
written,
it
will
be accompanied by the name;
given verbally without the name, the description will often bring recognition. Such a description will be meaningto the however, layman. less,
but even
if it is
These may be photographs, drawings, or For individual plants and for species, coloration is paintings. but Photographs and paintings show only the helpful expensive. and features do not bring out details of stamens and large, general or internal anatomy. These may, however, be shown in pistils Illustrations.
fine,
detailed drawings.
Illustrations are used mostly to supple-
ment worded descriptions. Drawing of flowers or entire plants by students in the laboratory has been largely abandoned because of the time required and the inability of most students to produce good
results.
Many years ago the happy idea was conceived of representing the essential features of floral morphology by rather simple diagrams of cross sections, more rarely longituFloral Diagrams.
dinal sections, of the flower.
numbers and union
In this
way such
characters as
symmetry, and most others can be a who is not an artist and in much less time represented by person than
is
of parts,
required for perspective drawings, although these dia-
IDENTIFICATION OF FLOWERING PLANTS
39
FIG. 5. 1, 2, 5, and 6 are terminal flowers; Representative floral diagrams. 3 and 4 are axillary the stem is represented by the black dot above and the leaf in the axil of which the flower is borne is shown below. 2, 1, Ranunculus. Geranium. 3, Pentstemon (irregular). 4, Lilium. 5, Sanguinaria. 6, Taraxacum, with calyx a pappus represented by dots, co, corolla; *, stamen; o w, ovary wall; on, ovule; r, receptacle.
A TEXTBOOK OF SYSTEMATIC BOTANY
40
grams are not rated an this
method
beautiful.
Some
institutions
of description in the laboratories, others
make
more general application than it receives. Floral Symbols and Formulae. Some years ago Dr. Clements proposed a method of describing species and
is
worthy
use of
do not.
It
of
F. E.
larger categories of flowering plants that has found favor with many botanists. Morphological characters such as calyx, pistils, and stamens are represented by suggestive letters (CA, P, and S), the
by figures. A few other dismarks are used also. These are the 'symbols,' and tinguishing combinations of them make up the 'formula,' which stands for
number
of each being indicated
a definite species, genus, family, or order. The system seems at first somewhat complicated, but the symbols required are rather few, generally suggested by the letters With a little practice the used, and therefore easily learned. student can describe a species more quickly by this method than by any other. Formulae for families offer a little more difficulty because of the fact that the members composing them are not all alike and it may be hard to provide for exceptions. For example, 4 nearly all of the Cruciferae have four petals, Co but Lepidium ' The symbol Co 4 could be used, but apetalum has none, Co this might give the impression that an apetalous condition in the flowers of Cruciferae is more common than it really is. Likewise, orders, which have even greater diversity of species than families, are still more difficult to represent by formulae, although it can be done 1 if a little allowance is made for unusual species in the order. ,
.
THE FLORAL CHART Clements also devised a
floral
chart to amplify the Besseyan and as
conception of the flowering plants. As he first depicted it, later modified by other taxonomists, it serves both as a families or orders
key to
and as a graphic representation
of relationships. of Bessey, lines are
Across the branching phylogenetic system irregularly from left to right, each representing an important character. For example, all families or orders below a certain line have regular corollas, while those above it have irregular All below another line have carpels distinct, while all corollas. above it have them united. By noting that these lines cross the
drawn
l See Raymond J. Pool, 'Flowers and Flowering Plants,' 2d ed., chart opposite p. 159, McGraw-Hill Book Company, Inc., 1941.
IDENTIFICATION OF FLOWERING PLANTS
41
KEY TO FLORAL SYMBOLS AND FORMULAE r^n v>u v -'
CO
5
Corolla, petals
(JOZ
^
Corolla of 5 united
j$
petaU
jr Ejwgynous, inferior
P
Stamens many
Pwti^many.unicttrpeUfttt
Pi Carpels
Corolla sygomorphic
Stamens
SO Scales
10,
P
anthers
united
O2+4
Stamens
6, in
two
I*iirtil
united at ba*e
one, tricarpellate
Patil one celled,
sets
tri-
carpellate
Stamens
P
5,
S Pistils
((ii))
(
'7^~ Stamens
Platil late,
epipetalous
tricarpel-
r-
1
celled
carpels
QNone
CA3 Co 3 S 6 P
6 One to
1
2+3
Organs in two
X Few, 00
Complete flower, 4 sets of floral parts attached to receptacle
five
seta
scales 2-4, Incomplete flower, ovary one-celled but tricarpellate
variable
Many,
variable
zygomorphic with 3 sets of stamens in 2 sets, 9 united
Corolla
petals; by their filaments
O,
(
)
XN
United above
^^
United at base
CA p Co 5
S5
United
CA5Cop epipetalous, pistil bicarpellate
Semens
Imperfect flower; stamens missing ; calyx represented by a pappus; ovary inferior, one celled but bicarpellate
(
)
The
exceptional condition
or
CA CoP 6
CAX
Sepals several
C AP
Calyx a pappus
CO
Apetalous
Cozi
or
Imperfect flowers, either staminate or pistillate
Corolla
Ovary 5 Petals
4-6 united
actmomorphic
morphic: stamens ovary inferior
inferior,
usually five car-
pellate but rarey with one cell 3-5 carpels
and
Fl
7
rs
Petalous
or
zygo-
epipetalous;
42
A TEXTBOOK OF SYSTEMATIC BOTANY
*ZYGOMORPHIC
'SOME MEMBERS ZYGOMORPHIC fEPlGYNOUS
FIG. 6.
Floral chart of the families of Angiosperms discussed in this book
arranged essentially according to the system of Bessey. The left-hand branch represents the Monocotyledons and the other two main branches the DicotyleThe broken cross lines show that the same evolutionary phenomena have dons. occurred repeatedly in different groups of higher plants. Important exceptions are recorded in notes in the lower right-hand corner, but occasional species showing deviations from the rules occur in many other families.
IDENTIFICATION OF FLOWERING PLANTS several branches of the phylogenetic system,
it is
43
seen that the
same evolutionary changes, e.g., irregularity of flowers, union of carpels, and unisexuality, took place repeatedly in different phylogenetic lines and at different times, as processes distinct from each other. Floral charts have been made for both families and orders and are convenient instruments for keying plants to their groups. Charts for orders are simpler to follow than those for families,
because there are fewer orders than families in the class Angiospermae, but they are usually of less value, since most manuals have keys for tracing members of the families to genera but few or
none for tracing members of orders to families. Therefore, tracing the plants to the order by means of the chart does not aid in the identification. Floral charts, like keys, are easier to make and easier to use if Such small, with few families, than if large, with many families. a chart, constructed to include all the angiosperm families of the entire world, If this
for pages the size of an ordicould be placed on a large wall chart.
would be too extensive
nary textbook, although
method
it
of portrayal
becomes generally popular, manuals
may adopt it for the families found in the limited area covered by the book.
The example given on page 42 makes no pretense of completeness for the entire United States but includes most of the large and important families and
will
serve to illustrate the principles
included.
A
difficulty arises
when the members
of a
group vary with
This is respect to a character used as the basis for a cross line. In the order illustrated especially well by irregularity of flowers. Rosales most of the families have regular flowers, but those of Leguminosae are irregular. In Ranunculaceae the flowers of
Ranunculus and Anemone are regular, while those of Delphinium and Aconitum are irregular. It may be that with experience such characters will not be used as a basis for cross lines, or possibly orders and families will be subdivided on the basis of these characters, although this alternative seems hardly likely.
THE WORK OF SPECIALISTS
A number of large or difficult genera, e.g., Senecio, Carex, Pentstemon, Lupinus, Astragalus, and Poa, have been studied
44
A TEXTBOOK OF SYSTEMATIC BOTANY
with great thoroughness, each by a different specialist. The purpose of this work is to find where specific lines should be drawn, revise specific descriptions, make ecological studies on the different species of the genus, etc. In carrying on these studies the investigators have traveled
much,
collected widely,
and
visited
different institutions to
study the specimens in their herbaria. Such specialists have become authorities in their fields and have done much valuable work by identifying specimens sent them and verifying or correcting the names of the specimens in institutional herbaria. While much of their time is to the service of
given
others, they receive in return the benefit of studying a wide range of specimens.
CHAPTER
III
PREPARATION OF HERBARIA Not until the sixteenth century did botanists make any systematic attempt to preserve for future reference the specimens they studied. Prior to that time a few dried herbs intended primarily as a supply for medicinal purposes served occasionally as comparative material.
About
1550, Cesalpini and his Italian associates and a few European botanists began quite definitely to preserve some of the material they studied. The wisdom of this procedure was soon appreciated by others and herbarium making became a central
In every civilized country great feature of botanical work. today plant collections of untold value can be found. Probably the greatest is at the Royal Botanic Gardens, Kew, England, while in America the Gray Herbarium at Harvard University and the collections in the National
New York Botanical
Museum, Washington,
D.C., the
Garden, and the Missouri Botanical Garden
are outstanding.
Purposes
of Herbaria.
Words
are but poor instruments for
best description leaves much about the pages would be required to describe a pine
The
describing plants. Many plant unsaid.
tree completely, but species are so numerous that their descriptions must be brief. Furthermore, the different individuals of a
somewhat. No two are exactly alike. A specific Often the botanist description, then, is but an approximation. who describes a species is unduly impressed by certain features, especially conspicuous on certain individuals, while he overlooks, species vary
minimizes, or ignores other features. As a result other botanists find the specific description unsatisfactory or difficult to apply. Even drawings and photographs fall far short of what is desired in
showing individual variation and details of structure and development. In very many cases it is necessary to compare descriptions with actual specimens, many in number and from widely separated regions. This work is of the greatest importance and has 45
A TEXTBOOK OF SYSTEMATIC BOTANY
46
resulted in better descriptions and in the dividing and uniting of groups along more nearly correct lines. To do this revision in the field is usually considered impracticable because time there is too valuable, suitable equipment is not available, and weather conditions are
sometimes unfavorable.
Furthermore,
it is
less
expen-
sive to ship specimens to a few central points where they can be examined than to travel over the world to study them where they
As a
most comparative herbarium and the The man who works indoors too exclusively, howlaboratory. ever, has a narrowness of view that is likely to be evident in his Sometimes, indeed, laboratory and herbarium distincwritings. tions must be repudiated because of field observations, as when specimens taken from different branches of the same tree and studied separately have been given different specific names. The working herbarium of today is much used for comparison with new material. Botany is becoming more and more popularized and applied, and in many sections of the country much material of an economic nature is sent to state authorities for examination and report. This material is often fragmentary, It would lacking reproductive parts, and poorly preserved. grow.
result of centuries of experience made in the
studies for taxonomic purposes are
require a highly experienced systematist to identify it at sight or with books alone, but the average botanist with known specimens
comparison can determine most of it quite readily. Preserved specimens are also much used to show visitors, both professional and unprofessional, and have become important as a for
means of technical and liberal education. Methods of Collecting. A satisfactory
series in
any given
include specimens in every stage of growth and species reproduction and from different localities and habitats. The will
most satisfactory single specimen, if only one were available, would be in the late flowering stage, showing both flowers and young fruits, and collected from a normal ha' tat, but a considerable number of plants are required to tell the full story of a species in all its varying aspects. complete specimen includes all parts of the plant, even the It is impracticable to collect unbroken root systems, howroot.
A
Furthermore, most specific descriptions do not mention the roots at all. In some cases, however, roots and other under-
ever.
ground parts are necessary for
identification.
An
experienced
1'RKPAKATION OF IIKKKAKIA
47
know which groups require underground portions which do not and will be governed accordingly. The and in should every case collect enough of the root system of beginner an herbaceous plant to show its general character. For taxonomic purposes the specimens should be selected to represent the species rather than to suit the fancy of the collector. If few in number, they should be of usual rather than unusual collector will
FIG. 7.
FKI. 8.
types.
Trowel for securing underground portions of herbaceous plants. an instrument must be heavy and strong and made of good steel.
-Vasculum
It can be made of tin or of light galvanized iron and in any dimensions.
for collecting plants.
many specimens are available, On account of the limited size of
If
Such
they should include
al!
the sheets of mounting types. small individuals when largo to select is a there paper temptation kinds of plants fe being collected, but this must not be overdone.
METHODS OF PRESERVATION On account of the bulky nature of plants it has long been the custom to press them flat. Admittedly this distorts their shape, but it has been found to be the only practical method for use on a large scale. To produce good herbarium specimens the plants must be pressed before they wilt. The difficulty in doing this is
48
,1
TEXT HOOK OF SYSTEMATIC BOTANY
so great that wrinkled specimens are frequent in many collections. A common method is to collect in a tin vasculum and press
immediately on return from the day's trip. With care good results may be had in this way. Generally it is not advisable to wet the plants to delay wilting or to restore turgidity, since this increases the tendency to discolor in the press, although the use of a wet paper lining in the vasculum is free from this objection. The finest preservation can be secured by the use of a field press For in which the plants may be placed as soon as gathered. collecting in open country the automobile has become a convenience, but much important work must be done in places inaccessible to
FIG.
9.
it.
Field press for standard-sized drier.s. use of straps.
The
pressure
is
obtained by the
Methods of Pressing. A rather standard procedure is followed They are laid between sheets of newspaper,
in pressing plants.
or plain inner sheets of similar quality, which are alternated driers of heavy absorbent blotting paper and the whole covered with a board and weight. For use in a field press when traveling, ordinary press boards are too heavy, and slatted frames of wood, thin veneer board, or strong cast aluminum are much to be
between
In place of a weight the field press is held by straps or clamps. Drying is obtained chiefly by transfer of moisture from the plants into the blotters, and to get good contact and prevent wrinkling the weight should be as heavy as possible without preferred.
crushing the plant tissue. Difficulty is found in building up a press full of plants to a thickness of several inches. Since the plants are laid mostly in
the middle of the paper folders and
may
or
may not extend to the
PREPARATION OF HERBARIA
49
edges, greater pressure is applied to the center than to the margins, which are more or less empty. The author has devised press boards of thin
plywood or composition material, such as to inch in 'tempered presdwood,' with wooden strips thickness along the sides. Pressure of straps or weights on these strips forces a bend in the boards and increases the pressure on the
^
%
plants at the margins, thus preventing their shriveling in drying. To prevent discoloration and molding, the driers (but not the
inner sheets) of
must be changed.
The number and frequency
of
depend on the character of the plants and the dryness the climate. Changing every day for two or three days and
changes
will
FIG. 10. Improved plant press. The strips along the sides of the flexible boards give increased pressure at the margins where there is less plant material. This prevents the shriveling that occurs at the margins in the ordinary plant presses.
then two or three more times at longer intervals this
is
excessive for
most plants
in
an arid
is
region.
a good rule, but Considerable
judgment and a methodical system are required to secure good specimens with a minimum amount of labor. If the plants are fairly uniform in moisture content, all can be kept together and the driers changed at the same time. If some, like grasses, are
and dry while others are thick and succulent, can best be segregated, either when they are put into press or they when the driers are changed the first time. The succulent ones will require changing more frequently and long after the others relatively small
are safely dry. It is
very
difficult
to dry
some kinds
of plants
without their
blackening. Saprophytes without chlorophyll, such as Infiianpipe, succulent hydrophytes, and plants wet with rain or dew give
A TEXTBOOK OF SYSTEMATIC BOTANY
50
the greatest difficulty, and they must be treated accordingly. Experience has shown that some species discolor more than others of similar texture. Plants such as those just mentioned should have the driers changed two or three times a day for several days. The superior quality of the product amply justifies the addiEven this care will not completely prevent tional work. discoloration of
some
species.
Heat. Under some circumstances it is This method desirable to use artificial heat to facilitate drying.
Use
of
Artificial
is especially useful in very jiamp climates, when making extensive collections while moving rapidly from place to place, and
when
pressing specimens that are
known
to give trouble by
blackening.
The method is as follows: The specimens are pressed in the way for a few hours until wilted. Sheets of corrugated cardboard, smooth on both faces, or of aluminum with fine cross Some prefer to corrugations, are then put between the driers. omit the driers if cardboard is used. The press is then strapped usual
together again and hot air is forced through the corrugations. The best source of heat is an electric hot plate or toaster, since an oil heater or other open flame gives off moisture of combustion. Specially constructed, ventilated boxes with light bulbs in the bottom are recommended.
The heat does not readily pass through the narrow corrugaAt least three ways are used tions but has to be forced through. to accomplish this: (1) The press may be set edgewise over the source of heat, with the corrugations vertical, and surrounded by a canvas skirt to direct the hot air upward through the press. (2) The press may be put in an oven the heat of which is automatically controlled, and a small electric fan placed in the oven with it to force the warm air through. This is the best method for indoor work. (3) When an automobile is used in collecting, the press may be placed on the fender beside the hood in such a position that the heat from the engine is forced through the press. Most of the newer types of car do not give off heat from the sides of the hood, but the warm air of summer forced through by the motion of the car serves very well. In fair weather this method is
highly successful.
Small or rare specimens may be dried quickly with an electric iron, the plants being placed between layers of heavy cloth or oaoer. Drvine bv artificial heat is a ranid method, and after 6 to
PREPARATION OF HERBARIA
51
12 hours the plants are usually ready to be transferred to an ordinary press and finished with regular blotters.
Mounting of Specimens. When dry, the plants are mounted on sheets of heavy white paper to support them in handling. The '
MONTANA FLORA,
'
T
&&L<*
<^^^^ /O.
Form 767 (RlMt November 1M
HERBARIUM OF THE FOREST SERVICE
28700
o s S. DEPARTMENT OF AGRICULTURE ---fK^^^ .
Collector's No. .JPPP..
Date
' mbm>
Common name State
of collection
..
X.
Bragrostis cilianansis J>^1^ JLink. ..
-Montana-------
County . .Yellows tone .. Locality .RpRds.ijJ^.,..5.jnl A .Baat.of ..Li .yings ton .. Altitude .?QQQ
iUd
._.,-
..W.
planU
In

(Wd.
browx.
rara
i.JjWht'*
nrlly
found)
4A.V-F.*. Forage value Other data ..J)
*ii
Collector's
of
pUnt)
(Annum). biennUI. or pwtnultl)
(Otbw noU)
diMcrnltintion)
(Doniity in Unthi)
Use . Abundance
Distribution ..mp.i.st.jp.3,acas ^
park, etc.)
order of
name
(Fltfwtr color)
(Flowtrln* pwiod)
^^J^.^. MM! (Period o(
d-. A ._U-.
-iff
.K!f.i.A.l.Frpmr_oy. U.
.
COVCMNMCNT rRINTING OFPICC
8
1M1
FIG. 11. Labels of herbarium specimens. Upper, a poor label with inadequate data. Lower, the label used in the extensive collections of the U.S. Forest Service. It contains more ecological data than do most herbarium labels. is llj^ by 16 J^ inches. The plants are fastened to the sheets by glue or gummed cloth strips or both. The amateur should mount only one plant on a sheet
standard sheet in this country
no matter species,
how
small
it is
or
how many, presumably
are to be mounted.
of the
same
Failure to follow this plan has
52
A TEXTBOOK OF SYSTEMATIC BOTANY
frequently resulted in plants of two or more species, superficially resembling each other, being mounted on the same sheet. However, professional botanists who are authorities on the species often mount several specimens on a sheet. The label is preferably
attached to the lower right-hand corner. It is a great mistake mount plants on paper of a quality that will become yellow or brittle with age. This is a poor way to economize. Storage. In large institutional herbaria the mounted plants are usually kept in specially constructed herbarium cases. Steel is necessary for safety, since many herbaria have been destroyed by fire to the despair of their owners. The arrangement of specimens in the cases is partly a matter of convenience. Usually the families are arranged according to a well-known taxonomic system, most commonly that of Engler and Prantl, or, less frequently, that of Bessey, or sometimes a modification of one of these. Within the families, however, the genera are often arranged alphabetically, and within the genera an alphabetical to
arrangement of species
is
still
more common.
Subgenera are
usually ignored in the labeling of specimens and in their arrangement in the herbarium cases.
In damp climates especially, it is necessary to avoid basement More storage for herbarium specimens on account of mold. often, particularly in the south, the specimens are likely to be
some kinds of which eat the gum of the the pollen or other parts of the plants themselves. Four methods are in use to prevent insect depredations: (1) Poisoning of the specimens by dipping them in a 2 per cent solu-
damaged by
insects,
labels, others
made by adding one part two parts of 95 per cent alcohol. The specimens dry quickly between blotters under light pressure. The method is obviously unsatisfactory for specimens that have already been mounted on paper. (2) The use of chemicals that act as repellents to the insects. Of these, moth balls and naphMore thalene flakes have been much used in herbarium cases. tion of mercuric chloride in a mixture of petroleum ether to
a mixture of one part of paradichlorobenzene (dichlorito five cide) parts of naphthalene, kept in the cases and renewed once a year. They keep the insects away but do not kill them. Of these carbon (3) The application of insecticidal fumigants. effective is
can be placed in dishes or trays in the top compartments of the herbarium cases, and, being a bisulfide has
been most used.
It
PREPARATION OF HERBARIA
53
volatile liquid, it will diffuse downward among the plants. For the fumigation of small herbaria, transferring from the cases to a
box containing the fumigant and leaving oversometimes Carbon bisulfide has a disagreenight preferred. able odor and it is highly inflammable, making it dangerous for use in a room with an open flame. Furthermore, its insecticidal value is not as high as was once supposed. For these reasons it is being replaced by a mixture of ethylene dichloride three parts and carbon tetrachloride one part, which is extensively used in flour mills, is easily obtainable, and is not inflammable. (4) The use of Insects are killed by heat at a relatively low temperature. 1 heat. The plants are placed on shelves in an electrically heated steel case with a dish of water. Four to six hours at 60C. has been found to kill all troublesome insects and their eggs. tight sheet-metal is
The Preservation of Type Specimens. Type specimens are so valuable that they should be preserved with especial care. Pressed plants are extremely fragile and repeated handling, even though carefully done, will inevitably result in more or less damage. In many herbaria they are kept apart from the regular specimens in separate steel cases, and in recent years there is a tendency to keep each one in a separate cellophane envelope. Most herbarium curators will not permit them to be shipped for examination.
Labeling and Field Data. The minimum of information to place on each sheet is the botanical name of the specimen, the at least stating the county or locality as definitely as possible even the township the date of collection, and the name of the It is most unfortunate that so many herbarium specicollector.
mens bear no other data. Ecologists are now doing splendid work in showing the effects of habitat on morphology and also the distribution of species and subspecies according to habitat, and their work would be made much easier if all preserved specimens available to them bore data concerning soil, moisture, altitude, exposure, associated species, etc. There is not the slightest doubt that many individuals of the same species are masquerading under different names because of modifications produced by
environment. 1 See Hugh O'Neill, Heat as an Insecticide in the Herbarium, Rhodora, 40: 1-4, 1938. The design for an electric heating box is given here along with the method.
A TEXTBOOK OF SYSTEMATIC BOTANY
54:
Two methods collectors: (1)
for recording field
data are used by experienced
A field notebook can be kept in which appear num-
bers that correspond with specimens collected. The notebook contains much information, the pertinent part of which is later transferred to the herbarium label.
(2)
Printed forms with head-
ings indicating the desired information can be put up in convenient-sized pads, one being filled out and included with each
These slips are applicable to collections made with a but are not so good for plants collected in a vasculum. The field data should apply specifically to the individual plant in question, not simply to the usual habitat in which that species is
specimen.
field press
found.
The herbarium should be looked upon as a working tool, and its quality and condition will be reflected in the results obtained from its use.
GENERAL FEATURES OF SPERMATOPHYTA
75
sperms. Likewise, there is an erroneous tendency to use the term 'conifer' as synonymous with 'gymnosperm,' whereas it
should be restricted to the one order Coniferales. Most of the seed plants are autophytic, i.e., possessed of chlorophyll and therefore not dependent on organized material A few, however, are saprophytic or parasitic to a for nutrition. or less The great majority are terrestrial, but a degree. greater few have adopted an epiphytic habit, while here and there throughout the group members have invaded shallow waters and
become adapted to an aquatic life. The Spermatophyta form by far the largest
of the four divisions
kingdom, including nearly 200,000 species. These are grouped into some 300 families, of which approximately twothirds are represented in the United States. The number of families cannot be stated exactly, for authorities differ as to what of the plant
In some systems of classiconstitutes a family in certain cases. such families as Liliaceae, Rosaceae, Leguminosae, and
fication
Compositae, which contain largo numbers of genera, are preserved, while in other systems each of these is broken up into two or more smaller families.
The Spermatophyta
also
show the
of the four divisions of plants. trees, some of which are 30 feet or
any
greatest variation in size of
They include all of the giant more in diameter, and range
down to tiny flowering plants a fraction of an inch high smaller than the average ptoridophytes and bryophytes and much smaller than many of the algae and fungi. Some are called mosses by those unfamiliar with plant classification. In no other division is there growth by a cambium layer separating phloem and xylem, a character found in gymnosperms and most dicotyledons.
CLASSIFICATION OF SEED PLANTS
To show
the relationships recognized in the larger subdivisions of the seed plants, the following synopsis of classification is
submitted.
DIVISION
SPERMATOPHYTA
Plants with true roots, stems, and leaves that belong to the sporophyte generation, the gametophytes being reduced to very small size. Reproduction is by seeds, sometimes supplemented
by vegetative propagation.
76
A TEXTBOOK OF SYSTEMATIC BOTANY CLASS
I.
-GYMNOSPERMAE
Strobili unisexual or bisexual, the female producing naked ovules, i.e., ovules and resulting seeds not enclosed in carpels.
Vascular bundles collateral and arranged in a cylinder about a The xylem region contains tracheids but no tracheae in pith. the secondary xylem (excepting in the Gnetales) (see page 89).
The female gametophyte (except in Gnetales) is multicellular and contains several archegonia. The male gametophyte is very much reduced. In the orders Cycadales and Ginkgoales it produces motile gametes, indicating an aquatic ancestry, but in the higher Coniferales nonmotile germ tubes have replaced them. CLASS
II.
ANGIOSPERMAE
Plants with true flowers, each containing, normally, four whorls of floral organs. The ovules are enclosed in carpels that may be distinct or united into a compound pistil. The vascular bundles are collateral and either arranged in a cylinder surround-
The xylem region coning a pith or scattered through the pith. and tracheae. The female fibers tains gametophyte produces no archegonia and
is
reduced to eight
cells (or to
one
cell
with eight
The male gametophyte is the germinated pollen grain, with nonmotile cells usually three. Subclass 1. Dicotyledones. Floral parts usually in multiples Two cotyledons in each seed (rarely one). of five or four. Vascular bundles usually in a cylinder with a cambium layer separating phloem and xylem. Leaves with netted veins.
nuclei).
*
Subclass
2.
Monocotyledones.
Floral parts usually
in*
mul-
One cotyledon in each seed, often wilJh the tiples of three. rudiment of another. Vascular bundles usually scattered through the pith and without cambium. veins (rarely netted).
Leaves with parallel
CHAPTER
VI
FAMILIES OF GYMNOSPERMS The gymnosperms consist mostly of shrubs and trees, some of gigantic size. They were once the predominant vegetation of the earth but have long been gradually declining in numbers (see frontispiece). They are of ancient lineage, perhaps from as far
back as Cambrian times, some 400 million years ago, but reached the climax of their abundance in the Pennsylvanian (Upper CarSince that time boniferous) period about 250 million years ago. they have gradually become fewer, many species now being While other orders waned, the Coniferales entirely extinct. in increased number and size of individuals, and this has greatly become the predominant order of the class. General Appearance. In the general appearance of the vegetative portion some gymnosperms resemble large, coarse ferns,
some are suggestive of certain kinds of palms, while most of those the pines, spruces, in the North Temperate Zone are forest trees The familiar. most of us are with which great majority firs, etc., are evergreen, Larix spp. being an exception. Gymnosperms are the most ancient of the seed plants. There is no doubt that they evolved from pteridophytes, probably
heterosporous ferns, and the seven orders (three of them extinct) naturally into two groups or subclasses as indicated by Chamberlain. 1 These two lines may have originated separately Fossil evidence leaves the quesor as one that soon branched.
fall
tion unsettled.
The following classification work already cited:
Classification.
berlain in the
is
used by Cham-
Cycadophytes Order Cycadofilicales (extinct) Order Bennettitales (extinct) Order Cycadales CHAMBERLAIN, CHARLES
' J.,
Gymnosperms,
Press, 1935.
77
'
Stanford
University
78
A TEXTBOOK OF SYSTEMATIC BOTANY
PLEIOCENC
MIOCENE
OLI0OCENE
EOCENE
UPPFRCRETACfOWS
LOWfRCRHACEOUS
UPPER JURASSIC
MIOWE JURASSIC RHAETIC
LOWER TfUASStt (Z EC H STEIN
ROTHLIEGENDE3
(STEPHANIAN)
(URALIAN)
OR I; MIS5ISSIPP1AN
(KULM; UPPER DEVDHMN MIDDLE DEVONIAN
LOWERDEVONIAN FIG. 21. A conjectural position of the various gymnosperm groups in geoThe horizons were compiled by Dr. A. C. No6 from various sources. logical time. The comparative amount of space does not equal the comparative amount of time.
(From C. J. Chamberlain.)
FAMILIES OF GYMNOSPERMS
79
Coniferophytes Order Cordaitales (extinct) Order Ginkgpales (nearly extinct)
Order Coniferales Order Gnetales (nearly extinct)
A comparison of the size and general appearance Cycadophytes and the Coniferophytes is shown in Fig. general, the former is characterized by an unbranched trunk with large compound leaves and the latter by a branching trunk with small, narrow, simple leaves. ORDER This
I.
of the
In
22.
CYCADOFILICALES
order is probably the gymnosperms. Fossil remains are found in Devonian strata, and the origin of the group may have been still earlier. The climax of abundance and specialization occurred in the Carboniferous period, after which the decline was rapid. Many of the fern-like fossils commonly found in coal are Cycadoextinct
oldest of the
filicales,
as
shown by
their production of
seed, which caused the English botanists to
them 'seed ferns' (Pteridospermae). Vegetative Structures. The most
call
primitive of the group lacked the broad fronds characteristic of the ferns of today, having only small, narrow, branching leaf stalks, in which respect they were much like the primitive true ferns of the
same period. This suggests either that this ancient order of gymnosperms came
FIG.
22.
The
habit
and comparative size of members of the Cycadoand Coniferophytes phytes. (From C. J. Chamberlain.)
from primitive ferns or that the two had a common ancestry and followed a parallel course in leaf development until, in the Carboniferous period, broad fronds were the rule in both.
The some
it
fibrovascular system varied greatly with the species. was like that of our common ferns; in others the stem
lu
had
A TEXTBOOK OF SYSTEMATIC BOTANY
80
a cortex surrounding a stele of phloem and xylem with a cambium layer between and a pith in the center. Reproduction. In reproduction two kinds of spores were formed on the fronds or in place of them. Some of these were
produced in sporangia much
like those of ferns and functioned as in that some cases at least, to have developed pollen grains seem, motile antherozoids. Others were formed within scaly coverings
and produced ovules that, when fertilized, became seeds. These seeds became dormant shortly following fertilization, before an embryo was produced. ORDER
II.
BENNETTITALES
This order probably branched from the Cycadofilicales in the Carboniferous period, although no fossils have been found The maximum development occurred earlier than the Permian. in the Jurassic. Their end seems to have come in the Cretaceous Probably this order ran period, and all forms are now extinct. the shortest course, geologically, of any of the gymnosperms. They were abundantly distributed throughout the United States and Mexico, and some specimens have been found in Europe. Vegetative Characters. The commonest form of the Bennettitales was a stocky, unbranched trunk 2 or 3 feet high, sur-
mounted by a crown of large, pinnately compound leaves. However, some of the trunks were scarcely taller than broad, and in one genus the stem was rather slender and branched. Reproduction. The most characteristic structures of the Bennettitales were the strobili. They were very numerous in the A typical strobilus had the axils of the leaves and were bisexual. Above a rosette of leaves superficial appearance of a flower. there formed numerous compound sporophylls bearing sporangia These surrounded a central cone bearfilled with pollen grains. ing numerous short-stalked ovules, each having a characteristic micropyle. The presence of pollen tubes or antherozoids has not been established. formed.
Within the seed a dicotyledonous embryo was
The flower-like structure of the bisexual strobilus and the dicotyledonous seed have led some taxonomists to believe that the Bennettitales were the direct ancestors of angiosperms of the Magnolia type, but this idea is strenuously opposed by Chamberlain. 1 1
Loc.
tit.,
p. 59.
FAMILIES OF GYMNOSPERMS
4
ORDER
III.
81
CYCADALES
From
the fossil remains we find evidence that the Cycadales appeared in the late Carboniferous period, became more abundant during the early Mesozoic era, and then declined, leaving at the present time only one family with nine genera and less than a hundred species. They were formerly widely distributed and abundant. The living forms are mostly tropical and subtropical, being especially abundant in Mexico and the West Indies, South Africa, and Australia. In a few places they form a conspicuous part of the dense vegetation, but genIt is believed that their ancestors were erally they are scattered. first
Cycadofilicales.
B
A FIG. 23.
Sperrnatozoids of Zamia floridana. A, side view, showing spiral band of cilia. B, apical view. (Redrawn after Webber.)
Vegetative Structures. The vegetative structure of the living Cycadales is fern-like, with large, pinnately compound fronds and usually short, stout stems, although the stems of some fossil forms were very slender. They are seldom more than a few feet high. Reproduction. Among the fossil Cycadales the spores of some species were borne on the fronds, and in others they were in strobili.
In present-day Cycadales
all
species are
dioecious.
The female strobili of some species are of huge size, 3 The pollen grains germinate and form tubes that longer.
feet or
require
months to penetrate the nucellus, from which they absorb food and thus function as haustoria. In the basal portion of the pollen tube are produced motile antherozoids that are of unusual size and complexity. Some are actually visible to the unaided eye and bear hundreds of cilia. Following fertilization an embryo is formed that becomes dormant as the seed ripens an advance over the Cycadofilicales.
several
A TEXTBOOK OF SYSTEMATIC BOTANY
82
ORDER
IV.
CORDAITALES
Of the four orders of the coniferophytes, the Cordaitales is the only one that is extinct, although two others are nearly so. Like the Cycadofilicales, the Cordaitales appeared in the Devonian period or earlier, but whether the latter evolved from primitive members of the former, making the gymnosperms monophyletic, or whether the two evolved separately, making the class diphyletic, is still
uncertain.
The
Cordaitales reached their
maximum
profusion in the Carboniferous period, when they were world- wide in distribution, but seem to have disappeared in the Permian,
making them the
first of
the gymnosperms to become extinct.
In their prime the Cordaitales formed Vegetative Characters. of the trees being 100 feet high with trunks some great forests,
up to 3
feet in diameter.
The
leaves were simple
much as 3
feet in length,
ORDER
GINKGOALES
and
in
some
but more commonly the inches. were trunks bare for a consideronly a few Usually able distance, the upper half being much branched. Reproduction. The micro- and macrosporangia were borne in separate strobili; some species were monoecious while others were Both kinds of strobili were borne on stalks, the male dioecious. sporangia being more numerous than the ovules. Antherozoids have not been found, but it is believed that they existed. Study of the fossilized seeds has been rather meager, and embryos have not been found in them. species very large, as
V.
This order was never so abundant as those just described, number of species or wealth of individuals. It appears to have originated from the Cordaitales in the Carboniferous period and to have reached its greatest abundance in the Permian. At the present time only one living species remains, Ginkgo It is not even biloba, the maidenhair tree of China and Japan. certain that this tree is still found growing wild, although a few specimens have been reported in western China by travelers. Some authorities believe that this tree would have become extinct but for its culture as an ornamental tree. It is an interesting fact that this species has undergone no detectable change for more than 150 million years, nor is it known to have given origin to any other species, although some of the either in
FAMILIES, OF
GYMNOSPERMS
83
may represent other species of the same genus. Ginkgo has been very thoroughly studied and will be used as the biloba
fossils
basis for further description of this order. Vegetative Structures. Ginkgo biloba
is
a large,
beautiful
and introduced into many parts of the United States and Europe where the climate is not The leaves are deciduous and very characteristic in too severe. appearance. They are broad, rather thick, glossy, and fantree,
grown extensively
in the Orient
shaped, with conspicuous, dichotomously branched veins radiating from the end of the petiole to the margin. Many of the leaf The wood shows definite petioles are branched into two lobes.
annual rings and a small pith. Reproduction. The trees are dioecious. The male and female strobili, on separate trees, are borne on short stalks. The male strobilus is compact and consists of a large number of The sporophylls, each bearing, as a rule, two microsporangia. female strobilus is a loosely branching structure bearing a few
which are generally in pairs. pollen grains form germ tubes, which, like those of the cycads, function as haustoria in the nucellus, and two large
ovules,
The
antherozoids are produced in the base of each. In each of the ovules there forms an oval, many-celled gametophyte containing two archegonia. After fertilization, a
dicotyledonous embryo develops, and as the seed ripens, its outer It has a disagreeable portion becomes soft and fleshy like a fruit. trees are sometimes reason staminate for this and preferred odor, to pistillate for ornamental planting.
ORDER
The
best
known
of the
VI.
CON1FERALES
gymnosperms arc the
form almost the exclusive
forest type in
Coniferales, which
many
cold, semiarid
and are widely distributed, especially in the North Temperate Zone and extending to the arctics. The Coniferales appear to have come from the Cordaitales in the Permian period and to have reached their climax in number of genera and species in the Cretaceous, but they are still very abundant perhaps more in number of individuals now than in regions
1
prehistoric times.
The common name 'conifer' should not be used 'gymnosperm' but restricted to the order Coniferales. 1
as a
svnonym
of
84
A TEXTBOOK OF SYSTEMATIC BOTANY
A
Vegetative Characters.
few of the Coniferales are low
shrubs, but most of them are trees, Some of gigantic size, and The stem structure is essentially usually they are evergreen. like that of the dicotyledons, but the wood lacks the tracheae of angiosperms.
Reproduction.
There
is
considerable variation in the strobili
Some are dioecious but more are monoecious, and a few have bisexual strobili. The pollen grains produce The ovules produce archepollen tubes but no antherozoids. of the Coniferales.
gonia in which embryos are developed following fertilization. Since this order of gymnosperms is now more important than all the others combined, it will be described in greater detail.
1.
PINACEAE.
Pine Family
A
very important family of cone-bearing, mostly evergreen about 8 genera and 150 species. They are of world-wide distribution, extending even to lofty mountain sides and far into northern regions. The Pinaceae were more abundant during the later Cenozoic era (see page 78) than now, but they have held their own better than most of the gymnosperms, probably because of their greater adaptability to the cold, dry
trees, containing
climates that in most parts of the temperate zones replaced the subtropical conditions which prevailed before the Glacial epoch. The Pinaceae and other conifers may be looked upon as the
Even highest evolutionary development of the gymnosperms. of not direct the are the ancestors doubtless angiosperms so, they but rather a somewhat specialized side branch of the main genetic line.
Familiar Examples. The best known examples of the pine family are pine (Pinus spp.), Douglasfir (Pseudotsuga spp.),
hemlock (Tsuga spp.), fir (Abies spp.), spruce (Picea spp.), and larch or tamarack (Larix spp.). Stems and Roots. The Pinaceae are all woody and are, for the most part, stately trees with straight, slightly tapering trunks, sometimes more than 250 feet high and 10 feet in diameter. The
The wood of root system is generally wide-spread but not deep. the Pinaceae, like that of most gymnosperms (except Gnetales), differs from that of angiosperms in lacking tracheal vessels in the secondary xylem, their place being taken by tracheids.
All parts
FAMILIES OF GYMNOSPERMS of the tree contain intercellular resin ducts, functional in the old heartwood.
85
which become non-
The Pinaceae all have rather thick, linear, alternate In the pines they are lj^ to 12 inches long, but in the other genera they are shorter. This reduced leaf surface combined with a sunken condition of the stomata results in low transpiration, and the trees are thus able to survive in dry or frozen With the exception of the larches or tamaracks the Pinasoils. ceae are evergreens, i.e., they are clothed with foliage the year Each leaf persists on the tree from 3 to 10 years, dependround. In addition to the ing on the species, but ultimately falls off. regular foliage leaves the pines have scales, sometimes called primary leaves, on the buds and young shoots. These are In the pines the leaf relatively broad and thin, and deciduous. Leaves.
leaves.
bases are enclosed in sheaths
one, two, three, four, or five leaves (depending on the species) growing from each sheath. In the other genera the leaves are single. The evergreen species have leaves of a very dark green, giving a somber appearance to the forests that they compose. All members of this family are heterosporous, proStrobili. in male strobili and macrospores in female microspores ducing
both borne on the same tree. In the male strobili on the underside of each scale, and in the female strobili two ovules are borne on top of each scale. to 3J^ years after fertilizaSeeds. The seeds mature in strobili,
pollen sacs are borne
%
woody cones that open to In most species each seed bears a broad wing that causes it to spin around in falling and so delays its descent that even a light wind will carry it to a considerable distance. The seed contains a relatively large endosperm and a straight embryo, usually with several cotyledons. Economic Significance. The Pinaceae are of great importance to mankind. But for this family of trees our familiar frame tion.
They
are produced in large
release them.
Pine, fir, spruce, and hemlock are kinds of lumber, but they are than other abundant not only more do not warp badly when exposed to the weather. easy to work and The turpentine that is an essential ingredient of ordinary paint and the rosin of varnish are extracted chiefly from pine stumps.
buildings could hardly exist.
The wood because of
of this family is not of the highest grade for fuel, but its abundance in many regions where the hardwoods
A TEXTBOOK OF SYSTEMATIC BOTANY
80
and
is extensively used. Enormous making certain grades of paper. Lastly, the forests of pine and other conifers cover many dry, rugged mountain sides that would be desolate without them and thus conserve the moisture and beautify the landscape. Where mixed with the light-green, broad-leaved forest trees the darker colors of this family give a most pleasing effect.
are lacking quantities
a great asset are utilized for
it is
2.
TAXODIACEAE.
Taxodium Family
This family, once one of the most conspicuous on earth, is now reduced to eight genera, nearly extinct in the United States and
FIG. 24.
-Taxodium (Taxodiaceae) showing natural habitat in swamp. The of the roots projecting above the mud and water.
'knees' are formed by angles (After Bergen and Caldwell.)
widely scattered over the rest of the world. They are adapted to warm, moist climates, and throughout most of the Cenozoic era, especially the Miocene epoch, in the balmy climate that generally prevailed, their gigantic forms covered almost the entire Northern Hemisphere with a few extensions into the Southern. Familiar Examples. The Taxodiaceae are rare in the United States, being confined to two species of Sequoia, the big trees (S. gigantea (Lindl.) Decne.) and the redwood (S. sempervirens (Lamb.) Endl.) of California and Oregon, and two species of Taxodium, 7
baldcypress (2
.
distichum (L.) L. C. Rich.) and pondcypress
FAMILIES OF GYMNOSPERMS
87
(T. ascendens Brongn.)
of the southeastern states (not to be with the cypresses of the family Cupressaceae). confused Stems and Roots. The few remaining species of this family are trees, the best known of which are the sequoias of California. Some of these are 350 to 400 feet high and 20 to 30 feet in diamthe largest forms of life the earth has ever known. The eter largest sequoias are estimated to be nearly 4,000 years old,
having spent half their lifetime before the birth of Christ.
A wondrous
record of alternating prosperity and famine, as
drought succeeded favorable climatic conditions, can be read In Taxodium the in the varying widths of their annual rings. growth of anchor roots, going on for centuries under so great a weight, has resulted in huge gnarled buttresses at the surface of the ground.
Leaves. Strobili.
The leaves are linear or scale-like and alternate. Both male and female strobili are borne on the same
tree. There are several pollen sacs on the under side of each staminate scale and several ovules on the upper side of each The female strobili develop into woody seedovuliferous scale.
bearing cones. Seeds. The seeds mature either the same season or the second season following fertilization. There are three to seven on each scale. A narrow wing extends as a margin all around each seed
but is absent from the triangular seeds of Taxodium. Economic Significance. Were the trees of this family as abundant as those of Pinaceae, their value would be almost
in Sequoia
Unfortunately, they are restricted to a small area.
incalculable.
The redwood
of California, 8. sempervirens, furnishes It is reddish in color (except the quality.
lumber
of
unusual sapwood, which is nearly white), evenly grained, light in weight, but It is rich in tannic acid and resists rather strong, though brittle. of the Pinaceae. The lumber of woods than the better decay
not of such good quality. There is, however, sentiment against cutting these trees, for they are well-grounded the last of the noblest race of trees the earth has produced. Furthermore, these great trees when cut shatter almost like glass and the waste is enormous sometimes 60 to 90 per cent by the
8.
gigantea
older
is
methods
of lumbering.
The baldcypress (Taxodium)
is less
the sequoias, being found in the
restricted in its range than
swampy
regions of a dozen
A TEXTBOOK OF SYSTEMATIC BOTANY
88
somewhat The is slowly disappearing. from the woodman's axe, but and wood is of unusual quality, being heavier, harder, stronger than that of the redwood and resisting decay even better. It is greatly sought for structural work in contact with the soil, where decay is most destructive, for greenhouse work, for staves, and of the southeastern states.
Its haBitat protects it it
indeed for a wide range of uses.
In comparison with the sequoias is being made to conserve it.
of the Pacific coast, little effort 3.
CUPRESSACEAE.
Cypress Family
The family Cupressaceae is rather small, containing but ten genera, widely distributed over both hemispheres. Familiar Examples. The commonest examples of the Cupresare the cedars (Thuja and Juniperus spp.), junipers (Juniperus spp.), arborvitae (Thuja spp.), and cypresses (Cupressus sp.), but not the baldcypress (Taxodium distichum (L.) L. C. Rich.), which belongs to the Taxodiaceae.
saceae
Stems and Roots. Many of the Cupressaceae are handsome and some are large forest trees, the giant cedar reaching a The tissues are height of 200 feet and a diameter of 15 feet. resinous and in most species aromatic. Leaves. The leaves are small and linear, or, more often, scalelike and closely covering the twigs. They are evergreen, persistThey have an opposite or whorled ing usually from 3 to 5 years. arrangement on the stem, in which respect they differ from those of the Pinaceae and Taxodiaceae. Strobili. Some members are monoecious and others dioecious. The scales are few in number, each bearing either several pollen In most genera the ovuliferous sacs or one to many ovules. shrubs,
strobili
develop into small woody cones, but in Juniperus the round blue or reddish fleshy bodies commonly
scales fuse into
called berries.
Seeds. In the dry, woody cones the seeds generally produce narrow marginal wings. In the fleshy ' berries ' there are one to six seeds, which are wingless and usually angled. Economic Significance. The largest member of the family, the giant cedar (Thuja plicata D. Don), is a splendid forest tree growing extensively on the Pacific coast from Alaska to California.
wood
is
The
In general the but very durable.
others are smaller trees or shrubs.
light in weight, soft
and
easily worked,
FAMILIES OF GYMNOSPERMS
89
therefore, extensively used for shingles, fence posts, poles, ties, bridge work, and boats. Special uses are for cedar chests, It
is,
where the aromatic wood acts as a repellent to moths, and for lead pencils, which require a soft, smooth-grained wood. Cedar-
wood
extracted for technical purposes. Several of the smaller trees and shrubs are grown for ornamental purposes, but the red cedar (Juniperus virginiana L.), oil is
found extensively
in the eastern
United States,
is
an alternate
host for the apple-rust fungus and is being replaced species that do not have this objectionable feature.
ORDER
VII.
by other
GNETALES
The order Gnetales is very small. The living representatives belong to only three genera. Apparently originating as late as the Upper Cretaceous from unknown ancestors, the Gnetales have never been abundant or cosmopolitan. While they show some characters resembling angiosperms, their origin seems too late to permit their being ancestral to that class, ovules mark them definitely as gymnosperms.
Vegetative
Structures.
The
general
and
their
naked
appearance and habi-
tat of the three genera are so different as not to suggest
any
relationship.
Ephedra with twenty-five species is a low, profusely branching shrub with small, opposite leaves and xerophytic characters. It is found mostly in southwestern United States and Mexico, but there are scattered patches in South America, Europe, and Africa. Wehvitschia, having only one species, is a very strange-looking plant, with a thick
stem that scarcely
rises
above the surface
of
the ground and bears two great, opposite leaves, several feet long, that persist and grow slowly throughout the life of the plant, which may be more than a century. Its range is confined to the desert regions of southwest Africa. Gnetum is made up of at least thirty-four species, mostly climbing vines 50 to 100 feet long, with large, oval, entire leaves at the
having netted veins. Different species are widely distributed throughout the jungles of South America, Africa, India, and the South Sea Islands, but none have been reported from
tips,
North America, Europe, or Australia. Numerous vessels are formed in the secondary xylem, but
their
A TEXTBOOK OF SYSTEMATIC BOTANY
90
method
of formation is
somewhat
different
from that
of the
angiosperms.
Reproduction. All three genera are dioecious, but some species show occasional monoecious plants and even bisexual strobili. The pollen grains form pollen tubes but no antherozoids. Archegonia, usually two, are found in the female gametophytes of Ephedra but not in those of Welwitschia or Gnetum. Pollination
through a long micropylar tube. followed by the formation of embryos.
of all three takes place
zation
is
Fertili-
CHAPTER
VII
FAMILIES OF DICOTYLEDONS Of the two subclasses of angiosperms the subclass dicotyledons much the larger, and it is correspondingly more important. While it is supposed to have originated before the monocotyledons, it has now reached a somewhat higher stage of development.
is
That the
first dicotyledons appeared in the early perhaps the late Paleozoic, is generally conceded The oldest known fossils of this group are (see frontispiece). from the Lower Cretaceous rocks, but they show a degree of advancement that seems to justify us in believing that they had a long line of ancestors whose remains have not yet been found. It is pretty generally agreed that the dicotyledons came from gymnosperms of a type somewhat different from any existing forms. The anatomy and histology of the stem, the spore formaand the morphology of male and female gametophytes are tion, all in harmony with this belief, if we make due allowance for advancement in structure by both gymnosperms and dicotyledons In all since the time when the former gave origin to the latter. likelihood both groups were considerably different at that time from any forms now existing; and an attempt to trace the connection through species now living or through a fragmentary Some of fossil record is admittedly a treacherous undertaking. the similarities noted may represent only parallel, or in some
Origin.
Mesozoic
era, or
respects convergent, development of the two groups. There are two general beliefs regarding the genetic connection of the groups of gymnosperms on the one hand and of dicotyle-
Some hold
the view that primitive Gnetales Amentiferae, now represented by willows, On this hypothesis the unisexual strobilus of the birches, etc. Gnetales is equivalent to the ament of the Amentiferae, the apetalous unisexual flower of the latter being primitively simple The Engler and Prantl system rather than simple by reduction.
dons on the other.
gave
rise to primitive
embodies this supposition.
However, 91
on purely theoretical
A TEXTBOOK OF SYSTEMATIC BOTANY
92
grounds Engler had predicated the existence of a large and varied group of herbaceous 'protangiosperms' that gave origin to both the monocotyledons and the dicotyledons, the latter being No fossil remains of such ' protangiosperms ' polyphyletic. have ever been found, but the idea that the dicotyledons are Others maintain that polyphyletic seems to be gaining ground. the primitive Bennettitales or perhaps Cycadales gave rise to a
Cond Two conceptions of the evolution of the flower from the strobilus. FIG. 25. In the center is a strobilus. According to Engler, this contained only megaspores or microspores, and the entire strobilus developed into an ament, pistillate or staminate, each flower being apetalous and derived from a sporophyll of the ament. According to Bossey, the strobilus contained megaspores below and microspores above and developed into a single flower, the lower sporophylls becoming sterilized and forming sepals and petals, those next above forming stamens and the upper ones forming carpels. The axis shortened and became the strobiloid receptacle.
simple form of Ranales represented today
by the Magnoliaceae,
belief the bisexual According a with bisexual, symmetrical flower, .the homologous and petals sepals originating by a sterilization of the lower sporoThe system of Bessey is in harmony with this line of phylls. further maintains that apetalous and unisexual which reasoning, so through a process of simplification. become have flowers the It is beyond scope of a beginner 's textbook to deal ade-
Ranunculaceae,
strobilus
etc.
to
this
is
quately with all the families of flowering plants, and the student can best familiarize himqelf first with a limited number carefully selected
from
different parts of this great
group of plants and
FAMILIES OF DICOTYLEDONS
93
knowledge by more advanced study. To this end about sixty families have been selected for discussion in this chapSome are chosen because of the large number ter and the next. of species that they contain; others, because of their economic importance; while a few, not so common or so important, have
later extend his
All of those treated interesting peculiarities worthy of attention. here are found in the United States, and most of them are widely
distributed elsewhere.
The sequence in which these families are taken up follows the Besseyan system (proposed by Charles E. Bessey), which in the judgment of most American and some European taxonomists follows phylogeny most closely.
No
made
here to group the families into orders for some of the orders of the angiosperms are not clear-cut phylogenctic entities but are loosely and perhaps artificially associated families. As previously stated,
two
attempt
reasons.
most
is
In the
first place,
of our descriptive
manuals
of flowering plants either ignore
name them without
In the second description. place, a discussion of only sixty selected families would fail to bring out the significance of the orders. the orders or
Description. The dicotyledons have some families entirely woody and others entirely herbaceous, but in most of the families both woody and herbaceous members can be found. In many families herbaceous species only are found in the temperate zones, but woody species also are found in the tropics and subtropics.
Each seed contains two
cotyledons, which may or may not rise above the ground during germination. In rare instances one cotyledon is absorbed in embryonic development, or more than
The fibrovascular bundles are characteristically a hollow cylinder, similar to that in the gymnosperms, with a cambium layer separating the tissues into bark and wood and forming, in woody perennials, annual rings of growth. The center is occupied by a pith that is never actually large, although it makes up a considerable proportion of the stem in the elderWith few berries (Sambucus spp.), and it may be very tiny. form or branched in the leaves bundles the vascular exceptions netted veins. Dicotyledons are usually deciduous, the exceptions being a few evergreen shrubs and trees, probably derived from deciduous ancestors. In regions where the climate is uniform throughout the year, i.e., not divided into winter and summer or two are formed. arranged in
94
A TEXTBOOK OF SYSTEMATIC BOTANY
wet and dry, the distinction between deciduous and persistent leaves is not obvious. <*
/
1.
MAGNOLIACEAE.
Magnolia Family
Some of the latest phylogenetic systems of classification, notably those of Bessey and of Hutchinson discussed in Chap. XI, rank the order Ranales, or what is sometimes spoken of as the 'ranalean complex/' as the most primitive of the angiosperms. In this basal group the family Magnoliaceae (given the rank of
FIG. 26. Distribution of Magnoliaceae. The complete isolation of members of this family, considered in conjunction with the anatomical and floral structures, indicates that it is of very great antiquity. (After Hutchinson.}
an order by Hutchinson) with its woody structure and large simple flowers stands as the most nearly ancestral form of any now in existence. No one supposes that the first angiosperms were like the magnolias of today; the belief is rather that the trees and shrubs of this family have departed less from the original form than have the members of other families. This family at the present time is a rather small one consisting of only about 10 genera and 100 species. Their distribution is and with a few mostly subtropical tropical, remaining in the North Temperate Zone. There is evidence that the family originated near the Arctic Circle, perhaps in northern Canada, in the Cretaceous period or earlier, at a time when a subtropical climate obtained there, and that they then spread southward
FAMILIES OF DICOTYLEDONS
95
and westward.
Extremely abundant throughout most of the era, they might have continued to be a major unit of our forest flora but for the Glacial epoch which they were poorly equipped to resist. They are now recognized as beautiful survivors of a once noble race of trees. Cenozoic
Familiar Examples. The best examples are the magnolias (Magnolia spp.) and the tuliptree (Liriodendron Tulipifera L.), which is the ' yellow poplar ' of lumbermen but is not related to the true poplars (Populus spp.) of the Salicaceae. Stems and Roots. The Magnoliaceae are all trees or shrubs. Since we have in the United States only two genera, those cited as examples above, this description will be limited to them. The magnolias are best known in the southeastern United States where a half-dozen species are indigenous in moist, rich woods and have been freely transplanted to the old plantations and
Many public grounds for the beauty of their flowers and foliage. have been transplanted to California, also. Most of them are small trees rarely exceeding 60 feet in height and often taking the form of large shrubs. Of the tulip trees there are but two remaining species, one confined to the eastern United States and the other, so similar that it is sometimes classed as a variety, found exclusively in China. The tuliptree is of huge size, sometimes 200 feet high and 12 feet Even in rather limited shade, the lower branches in diameter. fall off when very young leaving a smooth, straight trunk almost to the top.
Leaves. Magnolias bear alternate leaves of enormous size, sometimes as much as 30 inches long and 1 foot wide, generally They are deciduentire, glossy-green above, thick, and leathery. ous in most species, but evergreen in M. grandifolia L. and somewhat so in M. virginiana L. Tuliptrees have large, thick, In both genera the leaves are lobed or cleft, deciduous leaves. petiolate, with prominent stipules that protect the leaf buds before expanding, and usually ensheath the stem at maturity. Inflorescences and Flowers. There is no definite inflorescence, the flowers being solitary but sometimes set rather close together near the tips of the branches. The flowers are the In some of largest and most showy of any of the woody families.
the magnolias, e.g., M. Fraseri Walt., they are as much as 10 In the tuliptrees the flowers are cup-shaped inches in diameter.
A TEXTBOOK OF SYSTEMATIC BOTANY
96
to 3 inches wide, depending on the degree of expansion. perianth consists of six or nine separate parts, all showy,
and 2
The
or the three outer ones green. They arer arranged in whorls of The flowers are bisexual three, the outer whorl being the calyx. with many unicarpellate pistils arranged spirally on a cone-
shaped receptacle and below the pistils.
many stamens
attached to this receptacle
FIG. 27. Magnolia Campbellii (Magnoliaceae). with perianth removed. B, stamen. C, seed.
A, vertical section of flower Z>,
section of seed.
(After
Hooker.)
Fruits and Seeds. Each flower produces many fruits arranged on the receptacle to form a cone several inches long. The individual fruit is a tiny follicle in Magnolia and a samara in In Magnolia the follicles dehisce and release one or Liriodendron. two seeds which remain suspended for a time by slender threads. The very small embryo is embedded in endosperm. Economic Significance. The tuliptree is of considerable value for its lumber. In this country it practically never makes solid forests but is found mixed with other deciduous trees, although in parts of Europe it forms dense growths. For this reason the supply is limited even within its range. Because of the freedom While it of the trunks froin branches the wood is clear of knots,
FAMILIES OF DICOTYLEDONS
97
not heavy or strong or beautiful in grain, there are few species it for certain purposes where a light, smooth, easily worked wood is required. Both genera, but especially the magnolias, are of surpassing beauty because of their big waxy-
is
that surpass
FIG. 28.
Liriodendron Tulipifera (Magnoliaceae). Twig, bearing flower and (Redrawn from Sargent.) (Three-fourths natural size.)
leaf.
white or yellow-tinted flowers and their great glossy leaves. It is unfortunate that their range and abundance are so restricted. 2.
BERBERIDACEAE.
Barberry Family
There are about 10 genera and 150 species of the Berberidaceae widely scattered throughout the Northern Hemisphere and South America but nowhere of sufficient abundance to form a major part of the flora,
A TEXTBOOK OF SYSTEMATIC BOTANY
98
Familiar Examples.
Japanese
Common or European barberry (Berberis
(Berberis
Thunbergii
DC.), Oregongrape (Mahonia spp.), and wild mandrake or May apple (Podophyllum peltatum L.) are familiar examples. Stems and Roots. The species found in the United States are vulgaris
all
L.),
barberry
In the woody genera the tissues of
shrubs or perennial herbs.
wood and bark
are yellow.
Leaves. In Mahonia the leaves are evergreen with sharptoothed margins and are pinnately compound. In Berberis
FIG. 29.
Berberis vulgaris (Berberidaceae)
.
(From Britton and Brown.)
they are unifoliate, only the terminal leaflet developing and the others forming one to five thorns at the base of an apparently simple leaf. In all members of the family the leaves are alternate or basal.
In Berberis and Mahonia the and are generally yellow. In other
Inflorescences and Flowers. flowers are borne in racemes
genera they may be solitary or variously clustered. The flowers are mostly small, bisexual, hypogynous, and regular, with distinct sepals and petals, the same number of stamens as petals,
which
vary from four to nine, and one unicarpellate pistil. and Seeds. The fruit of many species is small and and is generally classed as a berry. In other species
may
Fruits fleshy
FAM1L1KU OF DICOTYLEDONS a small capsule or an achene. endosperm and a straight embryo.
it
is
The
99
seed has a copious
Economic Significance. The cultivated barberries introduced fuom the Orient have been extensively planted in the United States for hedges and ornamental shrubs. Their rapid growth, tough wood, protective thorns, and bright-red berries make them almost ideal for this purpose. The common form (B. vulgaris L.) is the more vigorous, and a horticultural variety of has purple foliage. Unfortunately, B. vulgaris is attacked by the aecial stage ofPuccinia graminis Pers., the fungus that causes stem rust of wheat, and the perpetuation of this disease in the it
colder climates is
is
largely dependent on the barberry bush, which
necessary for a completion of the
hope for control lies
of this
wheat rust
Since cycle of the fungus. in the northern United States
life
in the extermination of the barberry, a vigorous national
campaign is being carried on to that end. The Japanese barberry and all other species of the Berberidaceae found in America are practically resistant to the rust. 3.
RANUNCULACEAE. CA3~
Co
'
S
P x-
Crowfoot or Buttercup Family or
The family Ranunculaceae contains about 30 genera and 1,200 species of world- wide distribution. They are especially prevalent in temperate climates and some are found in arctic and alpine
The affinities of this family with the Magnoliaceae are seen and both are classed in the large and somewhat varied easily order Ranales. regions.
Familiar Examples. In the crowfoot family, familiar examples the windflower (Anemone spp.), peony (Paeonia spp.), columbine (Aquilegia spp.), larkspur (Delphinium spp.), and ' virginsbower (Clematis spp.). Many of the buttercups' belong to the genus Ranunculus of this family, but some are unrelated, are
belonging to Rosaceae and other families. Stems and Roots. The Ranunculaceae are nearly all herbaceous and mostly perennial, but in Clematis the stem is somewhat
shrubby or takes the form
a woody vine, climbing by petioles that function as tendrils. In some genera, Actaea, Cimicifuga, and Thalictrum, the vascular system is not definitely cylindrical but the bundles are somewhat irregular like those of the monoof
A TEXTBOOK OF SYSTEMATIC BOTANY
100 cotyledons.
There
is
a marked tendency for the development of
rhizomes and fleshy roots in the perennial species. Leaves. Lack of stipules is the only characteristic feature of the leaves in this family, although in nearly all species they have an alternate arrangement. Generally they are large; but in
FIG. 30. Delphinium bicolor (Ranunculaccae). This species is representative of the low larkspurs, which include D. Menziesi, D. Geycri, and D. Andersoni. They are found in the plains and foothill regions, from the eastern slope of the
Rocky Mountains westward.
(One-third natural
shape they vary from broad and to
decompound
irregular
develop
entire, as in Callha natans Pall.,
as in Thalictrum.
Inflorescences and Flowers. inflorescence.
Many
There
species produce
clusters.
long
size.)
is
no uniformity as to
solitary
Delphinium, Cimicifuga, racemes and Thalictrum has
flowers,
others
and Aconitum much-branched
panicles.
The flowers are likewise variable. but in some species of
Generally they are bisexual, Thalictrum they are unisexual and
FAMILIES OF DICOTYLEDONS
10.1
FIG. 31. Delphinium cucullatnm (Ranunculaceae). The tall larkspurs which include D. trolliifolium and /). barbeyi, are found in sparsely wooded regions at rather high altitudes in the western mountains.
(One-tenth natural
size.)
A TEXTBOOK OF SYSTEMATIC BOTANY
102 dioecious.
The
three to fifteen.
sepals are distinct
and vary
In most species they are
in
number from The petals
petal-like.
vary from three, or rarely none, to fifteen or more. In one branch of the family, including Ranunculus and Paeonia, they are alike, forming a symmetrical flower. In the other branch, including
Delphinium and Aconitum, they are irregular, as are also the The stamens are numerous and distinct. The pistils vary in number from one to many and consist of separate carpels that may be slightly adherent, asm Aquilegia&nd Delphin-
colored sepals.
ium.
All parts of the flower are
Fruits
hypogynous.
The prevailing type of fruit is a follicle The different follicles may be adherent at
and Seeds.
with many seeds. the base to form a loose several-chambered capsule, or they may be distinct. If one-seeded, they produce achenes that are often plumed by a development of the style, as in Clematis and PulIn ^Lctaea and Hydrastis the fruit is a berry. The seed satilla. has a copious oily endosperm with a tiny straight embryo embedded near the apex.
The Ranunculaceae are best known Significance. for their flowers. Many of these, including peony, columbine, Economic
larkspur,
and
clematis,
are
extensively grown in dooryards.
As a family it has a negative value for pasturage, for although wild peony and a few other members contribute a little to the food supply on the stock ranges of the west, this is offset in considerable measure by the losses from eating the poisonous larkspur, Delphinium, all species of which are deadly to cattle when eaten in quantity. Sheep and horses seem not to be affected.
Aconitum
is
poisonous
also,
but
is
not so abundant and
is less
frequently eaten. Several important drugs are obtained from this family. The most useful of these are aconite, hydrastis, cimicifugin, and staphisagria. 4.
NYMPHAEACEAE.
Waterlily Family
As the name indicates, this is a family of aquatic plants. There are eight genera and fifty-two species widely distributed over the earth, most abundant in the tropics but extending well into the temperate zones. They live in shallow lakes, ponds, and
FAMILIES OF DICOTYLEDONS
107
Ulmus fulva (Ulmaceae). 1, branch with staminate and pistillate 5, twigs with flower buds staminate flower. 3, leaves 4, fruits. and leaf buds. 6, leaf scar and lateral bud. 7, leaf scar. (After Illick.} FIG. 34.
strobili.
2,
A
108
TEXTBOOK OF SYSTEMATIC BOTANY
Economic Significance. Interest in the Ulmaceae centers in the beauty of the elm trees and in less measure in that of the hackberries. Many make the mistake of trying to grow elms too A little use is far north and are disappointed in the results.
made of the lumber for chairs and other furniture. It is fairly tough but not handsome and it does not resist exposure to the weather. When well seasoned it makes good fuel and is much used for that purpose. 7.
GERANIACEAE.
Geranium Family
There are in the Geraniaceae only about 11 genera and 650 temperate climates and especially preva-
species, found mostly in lent in South Africa.
FIG. 35.
Geranium disaectum (Geraniaceae). c,
dehiscent fruit,
d,
seed.
a,
floral
branchlet.
b,
flower.
(After Jepaon.)
9
Familiar Examples. Wild geranium or cranesbill (Geranium spp.), cultivated geraniums (Pelargonium spp.), and storksbill (Er odium spp.) are the only
commonly found
members
in this country.
of the
geranium family
FAMILIES OF DICOTYLEDONS
109
Stems and Roots.
The plants are all herbaceous except a Our species are mostly perennial. few Fleshy roots and rootstocks are common. Leaves. The leaves are generally deeply cleft or even compound. They are alternate or opposite, petiolate, usually stipuexotic
half-shrubs.
and in most species thickly covered with glandular hairs. Inflorescences and Flowers. Cymes are the commonest form
late,
of inflorescence, but umbels are found in Pelargonium. The flowers are showy, generally regular, but slightly irregular in Pelargonium and Erodium, bisexual, and 5-merous. Each flower
The sepals are distinct or petals are separate and hypogynous. There are usually five, ten, or fifteen stamens, some of which may be abortive, or, as in Erodium, reduced to staminodes. The
is
borne in a pair of small bracts.
The
united at the base.
usually 5-carpellate with one style and a superior ovary. general effect of the flower, and indeed of the entire plant, is
pistil is
The
suggestive of the Rosaceae, but in Rosaceae the stamens are usually more numerous and the carpels numerous and distinct.
and Seeds. The fruit is characteristically a beaked with a persistent calyx on a long reflexed peduncle sugcapsule head and neck of a bird hence the name cranesthe of gestive In most species the capsule dehisces from the base upward. bill. Kach chamber contains but one seed, the other ovule having In Erodium a portion of the style remains attached to aborted. as a hygroscopic awn. The seed contains little or no the seed endosperm and an embryo that is usually curved. Economic Significance. Most of the Geraniaceae are palatable Fruits
to livestock
and make good
The flowers are handsome common greenhouse geranium is
forage.
and abundant. Probably the grown in more homes than any other 8.
LINACEAE.
The family Linaceae genera and about 150
is
flower.
Flax Family
a rather small one, containing only 9
species.
Familiar Examples. The best examples are cultivated flax (Linum usitatissimum L.), wild perennial flax or Lewis' flax (L. Lewisii Pursh), and yellowflax (Linum spp.).
A TEXTBOOK OF SYSTEMATIC BOTANY
110
Stems and Roots.
The
species
found in the United States are
all herbaceous, although a few foreign species are shrubby. The plants are taprooted. Leaves. Por the most part the leaves in Linaceae are entire,
narrow, sessile, and alternate. Stipules are absent or fugacious. Inflorescences and Flowers. The flowers are axillary or terminal on the upper branches, which may be so close as to give a
corymbose or cymose
Pro. 36.
Linum
effect.
They
witati&timutn (Linaceae)
.
are
showy,
bisexual.
(from Britton and
hypogynous, and mostly 5-merous. The sepals and There are usually ten stamens in two whorls, the outer whorl being reduced to staminodes and the innet one regular,
petals are distinct.
united at the base. carpels,
giving the effect of encloses one ovule. varies
The
two to five united by a false partition Each apparent chamber four to ten carpels. The ovary is superior and the style number pistil is
each of which has
its
from one to five. and Seeds. The
Fruits
Apparently ten-chambered.
composed
of
cavity divided
which in flax is normally contains ten seeds and
fruit is a capsule,
It
FAMILIES OF DICOTYLEDONS
A
113
few important drugs are extracted from the leaves and the oil of citron, oil of bergamot, and oil of
rinds of the fruits, notably
lemon. 10.
EUPHORBIACEAE.
Spurge Family
The family Euphorbiaceae is a large and extremely variable one, containing about 250 genera and 4,000 species. They are of wide geographic distribution but are most abundant in the warmer climates, with few species extending beyond the Canadian border.
Familiar Examples. Familiar examples of the spurge family are castorbean (Ricinus communis L.), crownof thorns (Euphorbia splendens Bojer.), snow-on-the-mountain (Euphorbia margin-
and poinsettia (Euphorbia heterophylla L.). Stems and Roots. Most of the family are herbaceous, but shrubs and trees are not uncommon in the tropics. The juice is acrid and in many species milky from the presence of starch, gums, and resins. ata Pursh),
Leaves.
The
leaves are mostly simple, with an alternate,
opposite, or whorled arrangement, been reduced to spines.
and
in
some
species they have
As would be expected in so a is considerable there variety of inflorescence, but large family, are So rather cymes predominant. great a variation is shown in the flowers that only general tendencies will here be indicated. Inflorescences and Flowers.
Scarcely a statement can be made but will require exceptions. -For the most part the flowers are 3-merous. Perhaps the most
nearly
constant
character
and
is
the
tricarp>ellate
pistil.
The
specialization very marked. This reaches its climax in Chamaesyce where the flowers have neither petals nor sepals and are unisexual, the staminate flower consisting of a receptacle and one stamen, and the pistillate flower a In some species the leaves peduncle, a receptacle, and a pistil. or are white under the flowers just red, giving the plant a striking
tendency to reduction
is
appearance.
and Seeds. The characteristic fruit is a three-chambered capsule, each chamber containing one seed, or the carpels may separate into three nutlets. The seed has a straight embryo and contains endosperm that is usually oily. Fruits
A TEXTBOOK OF SYSTEMATIC BOTANY
114
Economic
Significance.
The Euphorbiaceae
contribute but
little to the food supply, although tapioca and other products of the fleshy root of Manihot utilissima Pohl. are worthy of mention. NotwithIn general the herbage is unpalatable to livestock.
standing
FIG.
its
deficiency in edible plants, this family
is
one of the
A, inflorescences in hypericifolia (Euphorbiaceae). C, single inflorescence (cyathium). D, stamen. E, fruit. F, axis of fruit. G, portion of fruit. H, seed (external). I, seed (internal). J, inflorescences and flowers of E. peplis. (After Rendle.} clusters.
38.
Euphorbia
B and
most important to mankind because of the commercial and medicfrom the milky juice, the seeds, and the tissues of its numerous members. First in rank is caoutchouc, into manufactured which, being rubber, needs no introduction to any reader. It comes from the milky juice of several species of Hevea, Mabea, Manihot, and Sapium. Wood oil, artist's and other drying oils, some of which are even better oil, tung oil,
inal products extracted
FAMILIES OF DICOTYLEDONS
115
than linseed oil, are extracted from the seeds of several Powerful drugs, especially those of a cathartic or species. irritant nature, are produced by many members. Probably no other plants have been used in the crude state for medicine so much as the Euphorbiaceae. Their properties have been discovered by natives the world over. In this country we now use for paint
castor
oil,
croton
cascarilla, hurta,
oil,
number
considerable
of
and other products.
A
deadly poisons are produced by exotic
members of this family. Of these some are especially injurious through the stomach, others through wounds or when applied to the skin, and others are blinding to the eyes. It is not surprising, therefore, that they should have been used so much for warfare, murder, and suicide, and to kill fish, game, and insects. Because of the brilliant color of the leaves surrounding the The flowers a few species are used for ornamental purposes. best
known
of these is the greenhouse poinsettia.
The crownof-
weird, bare, spiny stems and gay floral bracts, is as a house plant, and the castorbean is found grown frequently in thousands of dooryards and flower gardens. thorns, with
its
11.
VIOLACEAE.
Violet Family
CA 5 Coz 5 (Co 5 )Sj5P(i :3 )
The Violaceae
include about 15 genera and 400 species, which
are widely distributed.
Familiar Examples.
Violets
tricolor L.) are familiar
examples.
(Viola spp.)
and pansies (V.
Stems and Roots. The representatives found in this country all herbaceous and mostly perennial, but a few tropical forms
are
are shrubby.
Leaves. The leaves are simple and variously toothed, with a marked tendency to be cordate in form. They are petiolate with usually permanent stipules. In many species they are all
but in others alternately arranged. As a rule the flowers are solitary on long peduncles, but a few are racemose. In several of the genera the flowers are regular, but in Viola, the largest and best known genus, they are irregular with a spur on the basal petal. They are 5-merous except the pistil, which is tricarpellate. The basal,
Inflorescences and Flowers.
parts outside the pistil are free or slightly connate.
In some of
116
A TEXTBOOK OF SYSTEMATIC BOTANY
the violets two kinds of flowers are produced. Those that appear first are showy, as just described. They often fail to produce These are followed by apetalous ones that are self-fertile seed.
and produce many seeds. Fruits and Seeds. The fruit is a three-chambered capsule that, in some species, discharges the seeds with considerable The seeds contain endosperm and a straight embryo. force. Economic Significance. The Violaceae are chiefly valued for their flowers, the violets and the pansies, both of which are found There are in nearly all climates, even beyond the Arctic Circle. at least 200 species of Viola, and through hybridization and The violets selection hundreds of varieties have been produced. are mostly in solid colors of many shades, but in the pansies broken colors are the rule and these are of innumerable patterns. 12.
PAPAVERACEAE.
Poppy Family
Poppies, both wild and cultivated, are familiar to nearly everyThe family contains 25 genera and about 150 species.
one.
Familiar Examples.
Probably the
(Papaver orientate S.) is the species
large, red Oriental
poppy
most commonly grown
in
dooryards throughout the United States, but the yellow California poppy (Escholtzia californica Cham.) is found extensively
The opium poppy (Papaver somniferum L.) is widely cultivated in the warmer countries. The bleedingheart (Dicentra spectabilis Lem.), while differing in general appearance. belongs here, as does also the bloodroot (Sanguinaria canadensis
in the far west.
L.).
Stems and Roots. The Papaveraceae are mostly perennial herbs with a few annual species. The entire plant of some of the members of this family has a milky juice (latex), which varies in color from white to red. Leaves. The leaves are rather large, mostly alternate and simple, in some species lobed or cleft, and in a few species they are compound. Inflorescences and Flowers.
The
flowers of
most poppies are
solitary, but in the bleedingheart and some other species they are in racemes or panicles. They are quite variable. In the poppies
they are large and regular with four to six showy petals. In others the petals are much smaller; e.g., in the genus Dicentra,
FAMILIES OF DICOTYLEDONS
117
which contains the bleedingheart and Dutchmans-breeches, the calyx is reduced to two small scale-like sepals and the petals are in two 2-merous whorls, the two inner petals more or less spurred at the base forming a hood over the stigma. The stamens vary from 6 to many. The carpels are united, with varying numbers in each ovary. Fruits and Seeds. The fruit
a capsule, usually opening at the top and containing many seeds.
is
Economic plants are
Significance.
Few
more
significant to for good and for evil,
man, both than the opium
poppy. The contained in the milky juice of the fruits and from it are derived a number of prod-
opium
ucts,
is
most important
When
of
which
is
restricted to
morphine. Fl(i 39 _ Papaver somniferum medical Use they are of incom(Papaveracoae) (From Britton and rown -) but unfortunately parable value, they are habit-forming, and their misuse is so great that it is debatable whether the plant is more of a blessing than a curse. From bloodroot the emetic alkaloid sanguinarine is obtained. .
The
flowers of the poppies
and bleedingheart are among the
choicest. 13.
CRUCIFERAE (BRASSICACEAE).
Mustard Family
This important family contains about 200 genera and 2,000 They are widely distributed, especially in temperate climates. Most of them are mesophytic although some are semixerophytic. Foreign species are finding their way into this country, mostly through impurities in the seeds of crop plants, and many of those now here are becoming more thoroughly distributed as the virgin lands are brought under cultivation. Familiar Examples. Of the cultivated species, cabbage species.
(Brassica ol&racea var. capitata L.)
and wallflower (Cheiranthus
A TEXTBOOK OF SYSTEMATIC BOTANY
118
CheiriL.) are well known, while shepherdspurse (Capsella Bursaand the various wild mustards (Brassica
pastoris (L.) Medic.) spp.,
Sisymbrium
spp., Conringia spp., etc.) are
common throughout
weeds that are
the country.
Nearly all the Cruciferae are herbaceous few a shrubby species are known. They are usually although in some cultivated species the roots are fleshy. and taprooted
Stems and Roots.
Both annuals and perennials are abundant and a considerable number are biennials. Leaves. The leaves are simple, pinnately cleft, or compound, and without stipules. The arrangement is usually alternate but in a few species is opposite. Inflorescences and Flowers. In most Cruciferae the inflorescence is a raceme, but cymes are not
uncommon.
The
flowers are small
with four petals (rarely none), and four sepals, the inner two usually narrower than the arid regular
outer. There are six stamens in two whorls; the four inner ones are opposite the petals and have longer filaments than do the outer ones. The pistil is superior and composed of two carpels with one style and a
FIG. 40.
Floral (Cruciferae). longitudinal secflower below. (After
diagram above tion
of
Kobbins.)
stigma that is usually two-lobod but in some species is discoid. A false partition extends from one parietal placenta to the other, thus dividing the cavity into two cham-
The flowers are strictly hypogynous with all parts inserted bers. on the receptacle. Fruits and Seeds. Two types of fruit are found, long cylindrical siliques and short broad silicles. Some of the latter (e.g., in Capsella) have the partition through the short diameter and others (e.g., in Camelina) through the long diameter. The seeds are numerous, rounded, and without endosperm or with very
little.
The embryo
is
usually curved.
FAMILIES OF DICOTYLEDONS
119
Economic Significance. The family Cruciferae contains a few very useful members, contributing especially to the range of garden vegetables adapted to colder climates. Most of these are biennials, their value lying in the food stored the first year of growth.
Considerable variation
is
found
in the place of food
storage, fin turnip (Brassica Rapa L.), rutabaga (R. Napobrassica Mill.;, radish (Kaphanus sativus L.), and horseradish (Armoracia rusticana G.
M. and
S.) it is in
In kohlrabi (B.
the root.
In cabbage (B. oleracea caulorapa Pasq.) it is in the stem. capitata L.) and Brussels sprouts (B. oleracea gemmifcra Zenk.) it is
in the leaves,
and
in cauliflower
and broccoli
(B. oleracea botrytis
In watercress (Radicula NasturtiumBrit, and (L.) Rend.) there is no localized food storage^ aquaticum Some of the mustards, including wild turnip (B. campestris L.), field mustard or charlock (B. arvensis (L.) Ktze.), and black L.) it is in
the inflorescence.
mustard
(B. nigra (L.)
Koch) furnish considerable nectar that It is the more valuable from the fact that it is produced rather early, before the main honey flow in most sections comes on. Because of the small size of the flowers most species of Cruciforms honey
of fair quality.
forae are not especially ornamental, but a considerable number, wallflower (Cheiranthus Cheiri L.), stock (Mathiola spp.), candy-
amara L.), honesty (Lunaria annua L.), etc., have been improved to a point where they are handsome. The table mustard of commerce is obtained from the seeds of black mustard (B. nigra (L.) Koch) and white mustard (B. alba
tuft (Iberis
(L.) Boiss.).
Owing
to the acrid flavor of
most members
of the Oruciferae
they have a limited forage value. The wild crucifers are quite generally rejected, although turnips, rutabagas, cabbage, and rape are grown to a limited extent for stock feed. species of Cruciferae are distinctly poisonous. Because of their prolific seeding, quick growth,
None
of the
and adaptation
to a wide range of environmental conditions, many crucifers have become important weeds. Among the best known examples
are shepherdspurse (Capsella Bursa-pastoris L.), field mustard (B. arvensis (L.) Ktze.), tumblemustard (Sisymbrium altissimum L.), falseflax
(Camelina saliva
weed (Thlaspi
arvense L.),
(L.)
and one
Crantz), pennycress or fanof the worst of all weeds in
A TEXTBOOK OF SYSTEMATIC BOTANY
120
whitetop (Lepidium Draba L.), which not only seeds heavily but is a perennial, forming rapidly spreading For the most part the cruciferous weeds are pests of patches. broken ground. Few of them can make headway in a well-
some
localities,
established sod. 14.
CARYOPHYLLACEAE.
Pink Family
In the Caryophyllaceae there are about 70 genera and 1,400 species of world-wide distribution but most numerous in the North Temperate Zone. Familiar Examples. Familiar examples are pinks (Dianthus (D. Caryospp.), carnation phyllus L.), sweet william (D. barbatus L.), babysbreath
(Gypsophila paniculata L.), and cow cockle (Saponaria Vaccaria L.).
Stems and Roots. Caryophyllaceae are
all
The herba-
few species slightly woody at the base), annual or perennial, and usually enlarged at the nodes. The annuals are ceous
(a
mostly taprooted. Leaves. A 1 m o s t
without
exception the leaves are oppo- v site, rarely alternate near the
top of the plant. Agrostemma Cithago (Carand (From Brirton yophyllaceae).
entire,
Brown.)
sessile,
FIG. 41.
They
are
usually narrow and the pair at a node often
united to each other around Stipules are not formed in most species. Inflorescences and Flov ers. The inflorescence is usually cymose. The typical flower, as found in Cerastium, Agrostemma, the stem.
and Spergula,
for example, is regular, bisexual, and 5-merous, with five i.e., sepals, five petals, ten stamens, and five carpels. By reduction, however, various modifications of this plan have
developed.
Thus
in
white campion (Lychnis alba Mil.) the
FAMILIES OF DICOTYLEDONS
121
flowers are unisexual; in Loeflingia there are three to five stamens; in Scopulophila there are ten stamens, five of which are func-
reduced to staminodes; and in Sagina apetala Ard. and Achyronchia Cooperii T. and G. the petals are absent or reduced to minute scales. Other modifications could be enumThis lack of uniformity in the flower need not indicate, erated. however, that the family should be divided, for it is often a variation within the genus or even within the species, as in Stellaria media L. where the number of stamens varies from three to ten. As a rule the petals are separate and showy, the sepals are more or less united, and the ovary is superior with one cavity regardless tional
and
of the
number of carpels. and Seeds. The
five
fruit is generally a one-chambered dehiscent capsule with seeds varying widely in number. In some species, however, it is a utricle enclosed in a persistent calyx.
Fruits
The embryo
is
usually
wrapped around a
central endosperm.
The Caryophyllaceae are chiefly These are of many colors, solid or mixed, often of large size, and easily grown. The plants are unpalatable to livestock. Owing to their vigorous growth and These free seeding some members are objectionable as weeds. Economic
Significance. valuable for their flowers.
are especially chickweed (Stellaria spp.
and Cerastium
spp.),
corncockle (Agrostemma Githago L.), and cow cockle (Saponaria Vaccaria L.). 15.
CHENOPODIACEAE.
Goosefoot or Beet Family
The
goosefoot family consists of about 75 genera and 500 A few are semixerophytic species of world-wide distribution. and many are halophytic, i.e., especially adapted to growth in salty or alkali
soil.
Familiar Examples. Among the best known of the Chenopodiaceae are garden and sugar beets (Beta vulgarisL.), lambsquarters (Chenopodium album L.), Russianthistle (Salsola pestifer A. Nelson), greasewood (Sarcobatus vermiculatus (Hook.)
and summercypress (Kochia scoparia (L.) Schrad.). Stems and Roots. The Chenopodiaceae are mostly annuals, with some biennials and perennials, and a few shrubby species. Torr.),
While they vary considerably in texture, the majority are rather
122
.1
TEXTBOOK OF SYSTEMATIC BOTANY
As a rule they are taprooted and under cultivation the roots of some species become fleshy. Leaves. The leaves are simple and entire, or variously lobed, and without stipules. As a rule they arc glabrous, but in Chenopodium especially they are covered with a glandular, mealy
succulent.
The arrangement on
the stem is alternate, or, in a In some halophytic forms such as Sarcobatus, Salsola, Suaeda, A llenrolfea, and Salicornia they are much reduced in size, linear, or even scale-like. In such cases the stems perform largely the func-
pubescence.
few
species, opposite.
tion of photosynthesis, and transpiration is slow, to correspond
with
the
from
the
slow root
absorption
concentrated
soil
solution.
Inflorescences and Flowers.
The
flowers are usually borne in small axillary clusters or rather dense spikes or panicles at the
ends
of the branches.
apetalous
and usually
but not infrequently
and occasionally
They
are
bisexual,
unisexual
dioecious.
The
staminate flowers have a calyx of five or fewer sepals, usually more
One stamen is or less united. formed opposite the middle of each sepal, or in some species the number is fewer than the sepals. Beta vulgaris (ChenoFIG. 42. flower A, podiaceae). axillary cluster. B, same fusing to form 'seed ball.'* (After Robbins )
In the pistillate flower the calyx similar to that of the staminate
is
but it is lacking in certain from the ovary or nearly so. genera, e.g., Atriplex. The pistil is generally bicarpellate with one seed chamber, one ovule, and one to three styles and stigmas. The fruit proper, i.e., the ripened ovary, is Fruits and Seeds. a utricle, a small, dry, one-seeded fruit with a pericarp formed by a persistent calyx, expanded receptacle, or bracteoles, or some flower,
It is free
combination of these. In the beet these appendages envelop The genera vary as several fruits in one irregular 'seed ball.'
FAMILIES OF DICOTYLEDONS
123
to the presence or absence of endosperm, which, is surrounded by the curved or coiled embryo.
when
present,
Economic Significance. The Chenopodiaceae are of conBecause of the succulent nature siderable importance for food. of the young stems and leaves, and the lack of objectionable ' ' Spinach flavor, this family surpasses all others for greens. (Spinacia oleracea L.) and Swiss chard (Beta vulgaris var. Cicla L.) are the best examples, but garden and sugar beets and even wild forms such as lambsquarters and Russianthistle are much
used and very good. need no comment.
By
The
roots of garden beets as vegetables
most important member of the family is the sugar As a source of 'cane' sugar (sucrose) it is second only
far the
beet.
to sugar cane. Sugar beets do not yield nearly as heavily as sugar cane, but since they thrive in temperate climates while sugar
cane is confined to the tropics and subtropics they make a distinct addition to the total output of this sugar, i.e., about one-third. The Chenopodiaceae have considerable forage value. None
members is poisonous and a goodly number are abundant, and nutritious. Even Russianthistles are good forage The plants when young, and they have been used for ensilage. most valuable members on the stock ranges of the west are winterThe fat (Eurotia spp.) and the saltbushes (A triplex spp.). Chenopodiaceae are the more important because of their ready of the
palatable,
growth on lands so salty or so alkaline that most other kinds of vegetation cannot occupy them. A few of this family are troublesome weeds, particularly Russianthistle in the semiarid parts of the west and lambsquarters throughout the country. Both these weeds are annuals, intruders on exposed soil only, and quite unable to compete with the grasses
when the 16.
The
latter get started.
POLYGONACEAE. Buckwheat
family Polygonaceae
is
of
medium
Family
size,
having about 40
genera and 800 species. They are world-wide in distribution, the larger forms showing a preference for the warmer rather than the colder regions.
A TEXTBOOK OF SYSTEMATIC BOTANY
124
Examples. Buckwheat (Fagopyrum esculentum Gaertn.), rhubarb or pieplant (Rheum Rhaponticum L.), aad various kinds of dock (Rumex spp.) are familiar examples. Stems and Roots. Considerable variation can be found in Familiar
the vegetative structure of the Polygonaceae. The majority are herbaceous, but a few in the subtropics and tropics are shrubby and even tree-like. Of the herbaceous members some A few are vines, but are annuals, but more are perennials.
many more are erect. As a rule the stems are swollen at the nodes and in some the internodes are hollow. There is a strong tendency to the formation of red pigment in the epidermis.
FIG.
43
ABC
Rheum Rhaponticum
B, median longitudinal section. Lilrssen
C,
(Polygonaceae). A, flower, external view. with perianth and stamens removed. (After
)
Leaves. The leaves are entire or slightly lobed, rarely toothed or cleft. The arrangement on the stem is usually The stipules are alternate, but sometimes opposite or whorled. characteristic of the family with a few exceptions. They are broad and membranous and form a complete sheath (ocrea) around the stem. Inflorescences and Flowers. The inflorescences in the Poly-
gonaceae are quite variable, spikes, racemes, panicles, umbels, and cymes being common. The flowers are apetalous, with a calyx of two to six sepals, which are united in some species. The pistil is tricarpellate, or
occasionally bicarpellate as in Oxyria.
has one cavity and one ovule. The ovary is superior, with one to three short styles and usually three stigmas. While the flowers in most species are bisexual, in others they are unisexual and even dioecious. The sepals are often colored and It generally
FAMILIES OF DICOTYLEDONS petal-like, white, red, or purple, giving a inflorescence.
Fruits
The fruit is an
and Seeds.
tricarpellate
showy appearance
125 to the
achene, which in the usually
It may bear various three-angled. In the docks the three inner sepals grow up around
species
is
appendages. forming three wings. In Triplaris the wings come from the In Coccolobis the perianth becomes fleshy. three outer sepals. The seed contains a large starchy endosperm and a straight to
it
curved embryo.
Economic Significance. From a food standpoint the Polygonaceae contain rather important members. Buckwheat is extensively raised in the eastern United States, Europe, and It can be grown on very poor soil where few other parts of Asia. crops are profitable. The large petioles of rhubarb make a world-wide substitute for fruit in pies, preserves, etc. A con-
number of species, notably buckwheat, secrete abundant nectar that makes honey of fair quality, though rather dark. A few pernicious weeds belong to this family. Among these siderable
are wild buckwheat or bindweed (Polygonum Convolvulus L.), sheep sorrel (Rumex Acetosella L.), and wild begonia (Rumex For the most part the plants are unpalatable venosus Pursh). to stock though not poisonous. 17.
SALICACEAE.
CACoS
1 -x
Willow Family
or
The Salicaceae contain but two genera Populus, with about 30 species and several horticultural varieties, and Salix with over 190 species and many hybrids that make some sections of the genus difficult to classify. The family is a distinctly northern one, for, while representatives of both genera are found in the subtropics and even in the tropics, they are more numerous farther north and some species are found beyond the Arctic Circle and at the edges of glaciers high up in the mountains.
The race is an ancient one, both willow and poplar fossils being found in Cretaceous rocks. They were abundant throughout the Cenozoic era and withstood the glacial invasion of the Pleistocene epoch better than did most trees. Familiar Examples. The willows (Salix spp.) and the poplars (Populus spp.), some of which are also called cotton woods, are the only examples.
A TEXTBOOK OF SYSTEMATIC BOTANY
126
Stems and Roots. The poplars are all trees, the large ones more than 100 feet high and 6 feet in diameter. Some of the willows are trees as tall as the poplars, though not quite as large in diameter, but most of them are shrubs, some of the arctic and In general the alpine species being only a few inches high.
make
a rapid growth but are short-lived in comparison with the hardwood trees that make up the bulk of our deciduous
Salicaceae
forests.
Leaves. The leaves are alternate and simple, with variously toothed margins and a shape varying from narrowly lanceolate in the willows to nearly circular in some of the poplars. Stipules are produced by nearly all species, but in some they are small and In the willows the leaves are sessile or with short fugacious. The buds petioles, but in the poplars they have long petioles. are large and scaly, and in certain species of Populus coated with a yellow, sticky aromatic secretion. Inflorescences and Flowers. All the family are dioecious (or by exception monoecious) with unisexual apetalous flowers borne in aments which appear in the spring in advance of the leaves. They are borne singly, as a rule, on the previous season's growth, in the axils of the leaf scars. On the willows the aments, especially the pistillate, tend to be erect, but on the poplars they
are usually pendulous, especially the staminate.
The staminate aments vary certain willows to 4 inches in
in length
some
from
less
than
1
inch in
of the poplars.
They produce subtended by a bract. Each flower consists simply of a small group of stamens set in a cup-shaped, often Occasionsglandular disk. There is no recognizable perianth.
many
flowers, each
ally a bisexual flower or a pistillate flower develops in the staminate ament. The ament persists until the pollen is shed and then
drops.
The
pistillate
flowers each of
ament contains many very simple
which
Each pistil perianth. The to four stigmas.
but a
pistil in
Ordinarily the poplars are wind-pollinated and the insect-pollinated. Fruits and Seeds.
two valves. endosperm
pistillate
a concave disk without is bicarpellate, with a short style and two ovules are numerous in a single chamber. is
willows
The fruit is a small capsule dehiscing by The seeds are numerous, small, plumed, and without or nearly so. The embryo is straight. As soon
FAMILIES OF DICOTYLEDONS as the seeds are
duced them Economic
all
or nearly all discharged, the
127
aments that pro-
drop.
The Salicaceae are somewhat exactSignificance. ing in their ecological requirements. They must have sun, and yet they do not thrive in hot climates. With sufficient water they grow in almost any kind of
soil.
For these reasons
their
Where
other trees can grow these do not, except scatteringly along forest streams. Where other trees find conditions uncongenial, on the banks of prairie streams and in distribution
is
unique.
cold marshes, there
we
find poplars
and willows.
fore a distinct addition to the total of prairie regions of the semiurid west but for the poplars.
woody
They flora.
are there-
The
would be practically
vast
treeless
The wood of the poplar is distinctly inferior in quality, but for is much better than no wood. It is little used for lumber,
fuel it
but the quaking aspon and some other species, because of their and whiteness, are extensively used for paper pulp, The willow wood of which there is a shortage in this paper age. is likewise of low grade for fuel, although it was formerly much used for charcoal. In strength, however, it is much superior to poplar, a fact which has given it some usefulness for cricket and baseball bats, implements, chairs, etc., where small pieces can be utilized. Its greatest use is for basketry where it has played soft texture
a part since the dawn of civilization. In many parts of the world where the finer shade trees thrive the poplars are regarded as inferior, but in many regions not so blest they are extensively planted for the shade and beauty
The their rapid growth and dense foliage quickly provide. of known as the cotton cottonof the plumes seed, commonly which
woods, are so abundant in some species that they are distinctly The trees are propagated by cuttings, and where objectionable. these are taken from staminate trees only, this trouble is avoided.
The Salicaceae are not usually thought of as contributing much in the line of food, but in reality the shrubby willows furnish considerable browse for livestock in the mountainous regions of the west,
and keep many deer and other wild animals from
The poplars are grass. said to furnish a supply of winter food for the beaver. In sections where beekeeping is profitable the willows serve starvation
when deep snows cover the
A TEXTBOOK OF SYSTEMATIC BOTANY
128
the very useful function of supplying early nectar for brood rearing before most other honey plants come into bloom. 18.
ERICACEAE.
Heath Family
The Ericaceae as here treated include the Pyrolaceae, MonoThey have about tropaceae, and Vacciniaceae of some authors. 80 genera and 1,350 species, are world-wide in distribution, and are especially concentrated in Africa and southeastern Asia. are commonly found as an undergrowth in forests, but some
They
in the open. Familiar Examples.
grow
Well-known examples are trailing-arbutus (Epigaea repens L.), spicy or creeping wintergreen or checkerberry (Gaultheria procumbens L.), kinnikinnick or bearberry (Arctostaphylos uva-ursi
(L.)
rhododendron (Rhododendron
Spreng.),
laurel
(Kalmia
spp.),
spp.), azalea (Azalea spp.), huckle-
and cranberries (V actinium and Indianpipe (Monotropa uniflora L.) Stems and Roots. This family is essentially shrubby, witja a considerable number of woody vines and perennial herbs and a few trees. Leaves. The leaves are simple, often entire and sessile, exstiThe loaf arrangement pulate, and in most species evergreen. berries (Gaylussacia spp.), blueberries spp.),
is
commonly
alternate but
may
be opposite or whorled.
and Flowers. The inflorescence is varied, racemes, spikes, umbels, and solitary flowers being common. The flowers are polypetalous, or more often gamopetalous, ai^d They are mostly 5-merous or generally regular and bisexual. double the number of petals and sepals. with stamens 4-merous, Inflorescences
The
insertion is hypogynous.
and Seeds. The fruit is a capsule, berry, or drupe, with a straight embryo and endospermous seeds. Economic Significance. For flowering shrubs no family can compare with the Ericaceae. Their fragrant flowers, often in great clusters, and their glossy evergreen leaves give them a peculiar charm. They grow in great profusion out of doors, and Considerable honey is are extensively raised under glass. Fruits
obtained from various members of the family, and sourwood (Oxydendrum arboreum (L.) DC.) is reputed to be the most valu-
FAMILIES OF DICOTYLEDONS
129
130
A TEXTBOOK OF SYSTEMATIC BOTANY
able honey-producing plant in the southeastern states, both for
quantity and quality. The family has little forage value, but a considerable number of species are poisonous to livestock from the presence of andromedotoxin. The poisonous members include the laurels (Kalmia latifolia L., K. angustifolia L., Ledum glandulosum Nutt., Leucothoe Davisiae Torr., Menziesia glabella
Fia. 45.
Monotropauniflora
(left),
and Hypopitys lanuginosa
(right), (Ericaceae).
(After Dixon.)
Gray, Rhododendron albiflorum Hook., R. occidental^ Gray) and probably other species. In general they are unpalatable, but if feed is scarce sheep may be forced to eat them with fatal results. 19.
GENTIANACEAE.
Gentian Family
If the Menyanthaceae be excluded from the Gentianaceae, there remain in this family about 65 genera and 700 species.
FAMILIES OF DICOTYLEDONS They
are of wide geographic distribution but are best
131
known
in
temperate regions. Familiar Examples. The gentians (Gentiana spp.) and centaury (Centaurium spp.) are examples. Stems and Roots. The members of the Gentianaceae are herbaceous, the perennial species often producing juice of the plant is generally bitter to the taste.
practically
all
rhizomes.
The
Fia. 46.
Gentiana crinita (Gontianaceae)
(From Britton and Brown.)
.
The leaves are opposite and exstipulate, and mostly and sessile. In a few saprophytic species they are much reduced and destitute of chlorophyll, or nearly so. Inflorescences and Flowers. In some species the flowers are terminal and solitary, but more commonly they are in cymes. The flowers are typically bisexual and 5-merous, but the sepals, petals, and stamens may be reduced to four, or increased to as many as twelve, and the pistil is bicarpellate. The calyx and The stamens corolla are regular, of more or less united segments. Leaves.
entire
are attached to the throat of the corolla. in
most Fruits
The ovary
is
superior
species.
The fruit The seed, as a
and Seeds.
dehiscent capsule.
is
generally a many-seeded,
rule,
has a copious endosperm
A TEXTBOOK OF SYSTEMATIC BOTANY
132
with a small embryo, but exceptions are found in some saprophytic species.
Economic
Significance.
Formerly much value was
set
upon
the medicinal properties of various members of this family. Almost without exception they are so bitter that they are unpal-
Probably their greatest value beauty and abundance of their flowers. atable to livestock.
20.
OLEACEAE.
'
S2
1
lies in
the
Olive Family
~4
The members of this family differ so much in appearance that the layman would not be likely to suspect that they are related. There are about 20 genera and 500 species. They are world- wide, in both temperate
and subtropical
regions.
Familiar Examples. Growing wild or under cultivation in different parts of the United States are the ashes (Fraxinus spp.), lilacs
(Syringa spp.), privets (Ligustrum spp.), jasmines (Jasspp.), and the olive (Olea europaea L.) introduced from
minum
southern Europe into California. Stems and Roots. The Oleaceae are for the most part composed of shrubs and small trees, but some species of Fraxinus reach a diameter of 2
feet.
Leaves. In most species the leaves are opposite and simple, but in the ashes and a few others they are pinnately compound. In a few species they are persistent. Inflorescences and Flowers. The inflorescence is most commonly a panicle. The individual flowers are small, but handsbme In some species they are clusters may be formed, as in the lilac. apetalous. They are commonly bisexual but sometimes are unisexual and dioecious. Sepals, petals, and stamens are commomly two to four. The ovary is composed of two united carpels.
and Seeds.
In Fraxinus the fruit is a winged achene it is a drupe or a few-seeded berry. Economic Significance. Many members of the family have ornamental value as shrubs and trees. The privets are especially Fruits
(samara) in other genera ;
Ash trees desirable for hedges in climates where they thrive. make very good hardwood lumber, competing with oak. Olives are produced in large quantity for their fruits Eurooe. California, and the Orient.
and
oil
in southern
FAMILIES OF DICOTYLEDONS 21.
ASCLEPIADACEAE.
133
Milkweed Family
S5
CACOP There are about 280 genera and 2,000 species of world-wide most abundant in the subtropics and tropics.
distribution but
FIG. 47. A, inflorescences. B, Asclepias curassavica ( Asclepiadaceae) D, longitudinal section of flower. E, pollisingle flower. C, floral diagram. nium. fruit. Or, seed. (After Rendle.) .
F
t
Familiar Examples. Milkweed or silkweed (Asclepias spp.), pleurisy-root (A. tuberosa L.), waxplant (Hoya carnosa R. Br.), and carrionflower (Stapelia variegata L.) are examples of the Asclepiadaceae.
134
A TEXTBOOK OF SYSTEMATIC BOTANY
Stems and Roots.
The
species found in the United States are
mostly perennial herbs, but in warmer climates shrubs and shrubby vines predominate and a few species become small trees. The fibrovascular bundles are bicollateral in type, and the plants
Mexican whorled milkweed. Asclepias mexicana (Asclcpiadaccac). of this genus, several of which are poisonous, are widely distributed but are especially abundant on the open foothills of the western mounr tains. (One-half natural size.) (After Marsh.) Fio. 48.
The milkweeds
FAMILIES OF DICOTYLEDONS
135
with long, branching, laticiferous tubes which contain a starchy and albuminous milky juice. Rootstocks are common, and these may be long and slender for vegetative propagation, or fleshy and even tuberous for food storage. Leaves. The leaves are simple and generally entire, exstipuare
filled
and opposite in most species. Inflorescences and Flowers.
late,
The
inflorescence
is
mostly
umbellate, but sometimes cymose or racemose. The flowers are rather small, regular, bisexual, and gamopetalous. They are 5-merous, except the pistil, which is bicarpellate with a superior ovary. The filaments attach to the base of the corolla and are often united to form a sheath or column around the pistil, the anthers being pressed close to the style. Each stamen bears, on
anther like a hood. in
pistil, an appendage which enfolds the Similar appendages are borne on the petals These appendages collectively make up the
away from the
the side
some
species.
corona. Fruits
and Seeds.
The fruit is composed of two follicles, which
In Asclepias and some other or divergent. genera they are large and pod-like. Each follicle contains many The seeds, which commonly bear tufts of long, white, silky hair. and hard the and thin. is and straight, endosperm large embryo Economic Significance. For the size of the family the Asclepi-
may be close together
adaceae are relatively unimportant. They are unpalatable to and a few species of A sclepias are rather troublesome as weeds. Recently a method has been found for separating the mass of hairs from the seeds and so treating them that they make
livestock
good insulating material 22.
for lining jackets, etc.
CONVOLVULACEAE.
Morningglory Family
S5
About 45 genera and 1,000 species, most abundant in the tropics and subtropics but well known throughout the world. Familiar Examples.
Familiar examples of theConvolvulaceae
are morningglory (Ipomoea spp.), bindweed (Convolvulus spp.), some of which are often called morningglory, moonflower
(ColonyAction aculeatum House), sweetpotato (Ipomoea Batatas
Lam.), and dodder (Cuscuta spp.).
A TEXTBOOK OF SYSTEMATIC BOTANY
136
Stems and Roots. Most of the Convolvulaceae are twining herbaceous vines, but in the tropics some are shrubs, and a few are small trees. Often the vines are long and profuse, completely entangling the adjacent vegetation. A milky juice is not uncommon. The root system is very large. Sometimes the roots are long and slender, as in Convolvulus arvensis L., where they serve the purpose of vegetative propagation. Sometimes they are
Cuscuta (Convolvulaceae). A, parasite on willow. B, floral diaD, corolla opened. E, fruit dehiscing. F, seed. (?, embryo. and F after Peter. B, after Eichler. C, after Hooker. D, after ReichenF after Nees; arranged by Rendle.)
Fia. 49.
gram.
E
(A, bach.
C, fruit.
t
t
thick and -fleshy and of huge
size, as in Ipomoea pandurata (L.) /. and Meyer leptophylla Torr., where they store great quantities of food. Thick tuberous rhizomes are found in Convolvulus Scammonia. The dodders are parasitic vines twining about
various hosts, mostly herbaceous. Their color ish, nearly white, reddish, or orange.
Leaves. arranged.
The
On
is
leaves are simple, exstipulate,
very pale green-
and alternately
the dodders they are reduced to scales.
FAMILIES OF DICOTYLEDONS Inflorescences and Flowers. small cymes.
They
and bell-shaped, and
The
137
flowers are solitary, or in
are gamopetalous, regular, generally large 5-merous with a bicarpellate or tricarpellate
The calyx and corolla are inserted on the receptacle, and the stamens on the corolla tube, leaving the ovary free. There are from one to three long styles. Fruits and Seeds. The fruit is a capsule with two or three pistil.
or, by false partitions, apparently twice the number. Each chamber encloses one or two seeds, each containing a more or less curved embryo and scanty endosperm. Economic Significance. The sweetpotato is one of our most
chambers,
The fleshy roots are produced in abunOf subtropical dance, are rich in starch, and are of fine flavor. origin, they grow best in the south, although some varieties important vegetables.
succeed in the middle states. The term 'yam' is sometimes applied to the wetter fleshed varieties of sweetpotatoes, but it must be remembered that the true or Chinese yam is a mono[?otyledonous plant (Dioscorea Batatas Decne.). The vigorously growing vines and large, many-colored flowers
make the morningglories very fences, etc.
desirable for trellises on porches, Unfortunately the flowers wither quickly when cut.
A few members are pernicious weeds, especially the small or European bindweed (Convolvulus arvensis L.). The family has very
little
alfalfa
The dodders
of
somewhat and make trouble
in
forage value, although not poisonous.
and clover reduce the
yield
haying by binding the plants together. 23.
SOLANACEAE.
Potato Family
S5
S
The potato family is one of the best known, containing about 85 genera and 1,800 species. They are of wide distribution, especially abundant in the tropics and subtropics. Familiar Examples. Examples of the Solanaceae are potato (Solatium tuberosum L.), tomato (Lycopersicon esculentum Mill.), eggplant (Solanum Melongena L.), groundcherry (Physalis spp.), redpepper (Capsicum frutescens L.), and tobacco (Nicotiana
Tabacumit.).
Stems and Roots.
The Solanaceae
mostly herbaceous, but
in the tropics
temperate zones are many shrubby forms are
of the
A TEXTBOOK OF SYSTEMATIC BOTANY
138
found and a few small trees. The production of underground tubers, such as those of the potato, is exceptional. Leaves. The leaves are mostly simple, but sometimes deeply They are cleft, and in a few species pinnately compound. exstipulate and usually alternate. They are evergreen in a few genera, as Lycium. Inflorescences and Flowers.
The
inflorescence
is
generally
The or racemose, but solitary flowers are not unusual. flowers are often large and showy, regular or nearly so, gamopetacymose
lous,
and
bisexual.
There are
stamens, and a bicarpellate usually, a long style.
five
pistil
each of sepals, petals, and with a superior ovary and,
miMl port
FIG. 50.
Solanum tuberosum of flower.
Fruits
and Seeds.
(Solaiiaceae). C, floral diagram.
The
fruit. B, longitudinal section (After Robbins.)
A,
fruit is usually a berry,
tomato and eggplant.
sometimes
of
In those species where the pericarp does not develop a fleshy pulp, the fruit is a There are numerous seeds with fleshy endosperm and capsule. a curved or annular embryo. In some genera, such as Physalis, the persistent calyx develops a bladdery husk about the fruit. Economic Significance. The Solanaceae are of more than ordinary importance to the human race. They contribute heavily to the food supply through the potato, tomato, and eggIn the United States and Europe the potato ranks second plant. to wheat. Tobacco is a major crop over large areas of the country, nearly 2 million acres being devoted to it, although its value is debatable. Powerful drugs, mostly of a narcotic nature, very large size, as in
FAMILIES OF DICOTYLEDONS
139
and some of great value in medicine are characteristic of the The alkaloid solanine is found in greater or less quantity family. in many species, even in potatoes and tomatoes. Atropine, belladonna, capsicum, hyoscyamus, scopola, and stramonium are obtained from this family. Some of the members, including
all
the deadly nightshade (Solanum nigrum L.), are quite poisonous. Among the weeds belonging to this family, the jimsonweed (Datura Stramonium L.) is probably the most troublesome.
The large flowers and brightly colored berries make many Among species very attractive for flower gardens and dooryards. those worthy of mention are petunia (Petunia hybrida Vilm.), jessamine (Oestrum spp.), flowering tobacco (Nicotiana spp.), and Japanese matrimony vine (Lycium chinense Mill.). 24.
BORAGINACEAE. S
Borage Family
5
The Boraginaceae are prominently represented throughout the world with about 85 genera and 1,500 species.
Fio. 51.
Cynoglosaum
officinale
(Boraginaceae).
(From Britton and Brown.)
A TEXTBOOK OF SYSTEMATIC BOTANY
140
Familiar Examples. (Myosotis
(Heliotr opium
Leaves. narrow,
Bluebells (Mertensia spp.), forgetmenot
(Lappula spp.), and heliotrope peruvianum L.) are examples of the borage family.
spp.),
stickseed
The
leaves are simple, exstipulate, and usually and alternate, or the lower ones opposite and In most species they are pubescent or even densely
sessile,
petiolate.
hairy.
Most
Stems and Roots.
of the
borage family are perennial
herbs, a few being shrubs or trees.
Inflorescences and Flowers. istically
The
The
inflorescence
is
character-
a scorpioid cyme, which uncoils as the flowers open.
flowers are generally regular and bisexual. and often much elongated.
corolla are tubular
The calyx and The flowers are
5-merous, except the pistil, which is bicarpellate but usually with a four-lobed superior ovary. The stamens are inserted in the throat of the corolla. Fruits and Seeds. The fruit consists of four nutlets or drupeSome lets, which may, however, remain united in a single body. In some and others much. little or no have endosperm species the embryo
is
straight
and
in others curved.
The flowers, which are generally Significance. bluish or purple, are often highly decorative. Many species of Mertensia are excellent forage plants and grow abundantly Economic
around springs and 26.
in
marshy places
SCROPHULARIACEAE.
in
mountainous regions.
Snapdragon or Figwort Family
S 2-5
Of the Scrophulariaceae there are about 205 genera and 2,600 species. They are widely distributed but most abundant in temperate zones. Familiar Examples. Examples are snapdragon (Antirrhinum majus L.), butter-and-eggs or toadflax (Linaria vulgaris Hill), beard-tongue (Penstemon spp.), monkey flower (Mimulus spp.)? purple foxglove (Digitalis purpurea L.), mullein (Verbascum Thapsus L.), and Indian paintbrush or paintedcup (Castilleja spp.).
The Scrophulariaceae are mostly herbabut a few shrubs or trees. The tendency to degenerate are ceous, into a more or less complete parasite is found in about 15 per cent Stems and Roots.
FAMILIES OF DICOTYLEDONS
141
and species. The method of parasitism is similiar in the Orobanchaceae, viz., the roots from the found to that of the genera
germinating seeds attack the roots of various host plants. As illustrating the different degrees of parasitism, Gerardia flava obtains very little of its food from the host and can live independits absence; Pedicularis capitata and Odontites rubra are half-parasites with small green leaves and terrestrial roots; (?.
ently in
aphylla takes most of
FIG. 52.
Mimulus
c, pistil,
its
food from the host plant and has reduced
6, leaves, a, flowering branch. guttatus (Scrophulariaeeae). c, fruit (cross section.) (After Jepson.)
d, fruit (external),
pale leaves; while species of Harvey a and Hyobanche are wholly parasitic, destitute of chlorophyll, and bear scale-like leaves only.
The leaves
are exstipulate and mostly simple. Their or be on stem the may alternate, opposite, whorled, arrangement and some of Antirrhinum have the lower leaves opposite and the upper leaves on the same stem spiral. The leaves on the parasitic species are more or less reduced and poorly supplied with
Leaves.
chlorophyll.
Inflorescences and Flowers.
The
inflorescences are variable,
but racemes are very common. The flowers are bisexual, gamopetalous, and more or less irregular usually two-lipped.
A TEXTBOOK OF SYSTEMATIC BOTANY
142
There are four or
five united sepals, five united petals, two, four, The stamens are or five stamens, and a bicarpellate pistil. typically five, four of them in pairs of unequal length (didyna-
mous), but some have been reduced to staminodes or lost. The ovary is superior, and the stamens are inserted on the corolla tube. The fruit is generally a capsule bearing Fruits and Seeds. many endospermous seeds, with straight or slightly curved
embryos.
Economic Significance. The importance of the ScrophulariaAs forage plants most of the members is rather limited. are unpalatable and those that are relished do not recover well ceae
when cropped off. Their greatest value lies in their flowers, which show considerable variety of size, form, and color, and, as in the case of the Indian paintbrush, are supplemented by Two rather important drugs are obtained
large colored bracts.
from
this family, digitalis
not
many
escapes
are
noxious
and leptandrin.
For so large a family
Butter-and-eggs sometimes forms persistent troublesome
weeds.
from cultivation and
patches. 26.
OPOBANCHACEAE.
Broomrape Family
S2 + 2
OAt?Cozt?PO^) This is a small family of 11 genera and 200 species, which might almost be considered a subfamily or tribe of the Scrophulariaceae. Like most parasitic angiosperms they are not abundant over large areas but scattered widely. They are found most abundantly in the United States and Europe. ( Parasitism in the flowering plants most commonly takes three (1) In the mistletoes the seeds germinate on the bark of the which host, they penetrate directly. (2) In the dodders the seeds forms:
germinate in the soil and send up a twining stem that attacks the stem of the host, if a suitable one is within reach. (3) In the Orobanchaceae and some others the seeds germinate in the soil, forming seedlings the roots of which attack the roots of the host if
one
is
available.
In
all
cases success
is
dependent upon the right
species of host being close to the seedling parasite. Familiar Examples. In this country beechdrops
(Epifagus virginana L. Bart.) is parasitic on the roots of beech trees in the Cancer root (Conopholis americana (L.f.) Wallr.) is northeast.
FAMILIES OF DICOTYLEDONS
FIG.
53.
Orobanche
minor
(Orobanchaceae). (After Strasburger.)
Parasite
growing
on
clover
144
A TEXTBOOK OF SYSTEMATIC BOTANY
found in oak forests of the east, and broomrape (Orobanche spp.), Howparasitic on clover and other plants, is widely distributed. ever the majority of people in the United States have never chanced to see any of these plants. Stems and Roots. The Orobanchaceae are annual or perennial herbs, generally a few inches high, living parasitically on the roots of various host plants. Some are restricted in their parasitism to one species or genus of host plant, but others can attack a wider It has been shown that the seeds of some species of range.
Orobanche at least will not germinate except when in contact with the roots of a suitable host. The root of the parasite becomes specialized into a haustorium that penetrates the bark, and the plant, nourished by its host, grows into the air and passes through All parts of the plant are its vegetative and reproductive stages. destitute of chlorophyll, or white or brownish in color.
show mere
traces,
and arc yellowish-
Leaves. The leaves, like the stems, are white or yellowish, often with a tinge of red. They are small and scale-like and are only vestigial structures with little function. Inflorescences and Flowers. The flowers may be solitary, but more often they are in terminal racemes or spikes. There are four or five united sepals, and five petals united into an irregular, There are four stamens in pairs and often two-lipped, tube. often a fifth that
perigynous. general the
The
reduced to a staminode. Their insertion is In pistil is bicarpellate with a superior ovary.
is
flower
structure
strongly suggests that
of
the
Scrophulariaceae. Fruits and Seeds.
The fruit is a small capsule with many tiny in which the cotyledons are but slightly seeds endospermous developed.
Economic
The family
Significance.
is
interesting because of
economic significance because of the scarcity of individual plants and the fact that most hosts suffer little harm. its parasitic
nature but has
27.
little
LABIATAE.
Mint Family
CACOZP The mints are so distinctive in appearance and fragrance that they have been well recognized for centuries. There are about 170 genera and 3,000 species of world-wide distribution.
FAMILIES OF DICOTYLEDONS Familiar Examples.
145
Familiar examples are peppermint (Men-
tha piperita L.), catnip (Nepeta Cataria L.),
hoarhound (Marru-
bium vulgare L.), thyme (Thymus
vulgaris L.), sage (Salvia spp.) not to be confused with 'sagebrush' (Artemisia spp. of the family Compositae skullcap (Scutellaria spp.), and coleus
(Coleus spp.).
Stems and Roots. The Labiatae are mostly herbaceous, but a considerable number of shrubs and a few small trees are found in the tropics. The stems of the herbaceous species are com-
monly square.
The leaves are simple, exstipulate, and opposite, or, They are abundantly supplied with species, whorled. glands secreting volatile oils. Leaves.
in a
few
Inflorescences and Flowers.
The
flowers are generally borne
in small axillary cymes, which by their arrangement along the upper part of the stem often give the effect of a raceme. They
are bisexual, gamopetalous,
more
or less irregular,
and often
There are four or five sepals and petals, and four two-lipped. If there are but two they are often or two stamens in pairs. supplemented by two staminodes. a superior ovary.
The
pistil is bicarpellate
with
and Seeds. The deeply two-lobed capsular fruit breaks without The seeds have true dehiscence into four nutlets. up Fruits
or no endosperm arid the embryo is usually straight. Economic Significance. The Labiatae are chiefly valuable for their volatile oils, which are used for flavoring and for medicine. These are quite numerous and the list given above under familiar little
but representative. Additional products of medicmarrubium, hedeoma, and scutellaria. A few of the plants, such as coleus, are ornamental. The Labiatae quite generally yield nectar in abundance. The sages of California, examples
is
inal value are
especially the black sage (Salvia mellifera Greene), are among the heaviest producers, and the quality of the honey is excellent. 23.
The
rose family
1,200 species.
is
Its
ROSACEAE.
Rose Family
rather large, containing about 70 genera and are of world- wide distribution, only
members
about one-fourth being found in the United States. They have considerable variation in morphological characters, as shown, for example, by the fruit of the rose and that of the raspberry. Some
A TEXTBOOK OF SYSTEMATIC BOTANY
146
authorities consider the
Pomaceae and Drupaceae as
tribes or
subfamilies of the Rosaceae and claim that their separation is based on economic rather than scientific grounds, but the floral axis,
gynoecium, and fruits in these families seem sufficiently them as is done here and by a num-
different to justify separating
FIG. 54.
Rubua strigosua (Rosaceae). A, longitudinal section same of fruit, f, single pistil. (After Robbins.)
ber of other authorities. families
of flower.
JB,
Certainly the relationship of the three
is close.
Examples. Rose (Rosa spp.), raspberry (Rubus spp.), strawberry (Fragaria spp.), spirea (Spiraea spp.), and cinquefoil (Potentilla spp.), some species of which are called Familiar
buttercups, are among the numerous examples of this family. Stems and Roots. The Rosaceae are mostly perennial herbs,
but some species are shrubs and a few are
trees.
Many
of the
FAMILIES OF DICOTYLEDONS
147
shrubby forms are armed with spines which, in Rosa and Rubus, are protuberances of the cortex from both nodes and internodes. Trailing habit is not uncommon among both the herbaceous and the
woody
Leaves.
species.
Both simple and compound leaves are common, the With rare exceptions the leaves bear
latter usually pinnate.
stipules
the stem
The arrangement on few exotic species are evergreen.
that are generally persistent. is
alternate.
A
The
Inflorescences and Flowers.
inflorescence
is
variable,
corymbs rather predominating. The flowers are usually bisexual and tend to be 5-merous, but numerous stamens and unicarpellate genera such as Geum, Potentilla, and Rubus. For the most part the flowers are large, showy, and symmetrical, but in certain evergreen shrubs of South America th6y are somewhat irregular. In most species a central elevation of the receptacle is crowded with distinct unicarpellate pistils, but in the genus Rosa these are inside a cup-shaped pistils are characteristic of certain
Fragaria,
hypanthium. The fruit proper, i.e., the ripened pistil, is Fruits and Seeds. In Sicversia, typically an achene, a small follicle, or a drupelot. Geum, and some other genera the persistent style forms a plume on the achene. In Potentilla it is deciduous and the achene is naked.
In Fragaria the achenes are partly embedded in the surby a development of the receptacle.
face of a fleshy pulp formed
In Rubus the carpels form as many drupelets attached to an elongated receptacle, thus producing an aggregate fruit. In Spiraea the pistils form dehiscent follicles. In Rosa the hypanpistils and becomes fleshy with maturity, the achenes, the whole forming a pome-like fruit, the embedding well-known scarlet rose hip. The seed has a large, straight
thium surrounds the
embryo with no endosperm. Economic Significance. As a source of fruit this family has only two or three rivals; indeed it may be considered the most important family for
berries.
Strawberries, raspberries, logan-
and blackcaps, considered in the aggrevalue. As food for livestock the family are immense of gate, is of limited importance, for while mountain mahogany (Cercocarpus spp.), bitterbush (Purshia tridentata (Pursh.) DC.), and the wild roses make good browse, most herbaceous species are berries, blackberries,
unpalatable.
Many
beautiful flowering shrubs belong to this
A TEXTBOOK OF SYSTEMATIC BOTANY
148
Probably no other family, especially the roses and the spireas. single genus of plants is as much cherished for its flowers as Rosa. 29.
POMACEAE (MALACEAE).
Apple Family
Formerly a part of the Rosaceae, the Pomaceae are now on good authority given the rank of a distinct family that contains about 20 genera and 500 species of wide geographical distribution.
rim of
Fia. 55.
receptacle
Pyrus mains (Pomaceae).
Longitudinal section of flower.
(After
Robbing.)
Well-known examples are apple and pear mountainash (Sorbus spp.), hawthorn (Crataegus
Familiar Examples.
(Pyrus spp.),
and Juneberry or serviceberry (Amelanchicr spp.). Stems and Roots. The Pomaceae are all shrubs or trees, some
spp.),
of the older apple trees reaching a diameter of 2 feet or more. Most species of of all members is hard and strong.
The wood
Crataegus are armed with stout thorns that are morphologically lateral branches.
In most genera the leaves are alternate, simple, serrate or dentate, and sometimes slightly lobed. They are provided with petioles and small deciduous stipules. Sorbus Leaves.
FAMILIES OF DICOTYLEDONS
149
has large pinnately compound leaves with well-developed stipules that persist until the leaves are fully expanded. Inflorescences and Flowers, As a rule the inflorescence is a compound raceme. The flowers are regular, bisexual and
The tendency is to be 5-merous but the generally showy. stamens are rather numerous, and in some species the carpels are fewer than five only one in some of the hawthorns. The carpels are firmly united into a single pistil that has an inferior ovary and one to five styles. The insertion is epigynous sepals, petals, and stamens being attached to a well-developed hypanthium surrounding the ovary.
and Seeds. The fruit is a pome that may be very and pear, or small and berry-like, as in mountainIn most genera the carpels are ash, serviceberry, and hawthorn. There is no endosperm, thin and hard, as in the core of an apple. the straight embryo entirely filling the seed. Economic Significance. No other family compares with Fruits
large, as in apple
Pomaceae in the extent of its fruit production. Literally hundreds of varieties of apples have been developed, with a wide range of colors, sizes, and flavors. They can be grown in different climates and soils, keep longer after picking than most Pears fruits, and are more generally consumed than any other. are important also but their poorer keeping qualities and limited range of flavors rank them far below apples in quantity consumption. Apple wood is used a little for tool handles and makes
bloom is from the
when
The beauty
of apple trees in nectar is obtained worthy of mention, and considerable
excellent fuel
available.
flowers.
30.
DRUPACEAE (AMYGDALACEAE). Plum
Family
P1 Like the Pomaceae, the plum family was set off from the older Rosaceae. It contains 3 genera and about 120 species. Familiar Examples. The best examples are peach (Prunus persica (L.) Stokes), (P.
Armeniaca
L.),
and chokecherries Rydb.).
almond
plum
(P.
communis
(L.) Fritsch.), apricot
(P. spp.), cultivated cherry (P. spp.),
(P. virginiana L.
and P. melanocarpa
(A. Nels.)
A TEXTBOOK OF SYSTEMATIC BOTANY
150
Stems and Roots. All of the Drupaceae some of the wild black cherries growing 100
are shrubs or trees,
and 4 feet due to traces of prussic It also contains a glucoside, amygdalin, from acid and tannin. which prussic acid is formed through the action of an enzyme, emulsin. When wounded the bark exudes a gum that is sup-
The bark has a
iu diameter.
posed to protect
FIG. 56.
it
to
some
bitter taste
extent.
Prunua cerasus (Drupaceae).
Leaves.
The
feet high
Longitudinal section of flower.
(After
leaves are alternate, simple, petiolate, serrate,
and provided with small deciduous
stipules.
conspicuous glands are found on the petioles. leaves contain prussic acid and amygdalin.
Usually a few Like the bark the
The species vary in type of be It may inflorescence. umbellate, corymbose, or racemose, The flower is or the flowers may be solitary or in twos or threes. full set of floral usually regular and complete, i.e., bearing a Inflorescences and Flowers.
organs.
The
insertion
is
perigynous, leaving the unicarpellate
pistil free.
number
is
FAMILIES OF DICOTYLEDONS
151
The petal and sepal number is five typically ten, fifteen, or twenty.
and the stamen
Fruits and Seeds. The fruit is a drupe which is velvety in the peach and almond, but glabrous in most of the other species. The ovary wall develops into three layers, an outer epicarp or skin, a middle mesocarp or pulp, and an inner endocarp or stone.
In the almond the mesocarp is leathery in texture. Although pistil contains two ovules, usually only one forms a seed; the In the almond two seeds are not uncomother fails to develop.
the
They contain prussic acid and amygdalin in amounts varying with the species strong in bitter almond and apricot, but very little in the ordinary sweet almond. The seed is large but without endosperm. The seed coat is very thin, its function of protection being usurped by the endocarp of the fruit. Economic Significance. The Drupaccae rank second or third among the families in fruit production. Were peaches, mon.
and other stone fruits as good keepers after ripening as and oranges, they would probably be raised in greater apples abundance than either. Under the circumstances, the limiting factor in their production is the amount that can be consumed and preserved within a few weeks each season. Almonds are comcherries,
monly
classed as nuts although morphologically they are quite They are in such demand that the few regions of this
different.
country where the climate is suitable for their production are used to capacity. In the eastern half of the United States where cherry grows wild and produces large trees, these are valuable for lumber.
Cherry wood
and
is
reddish in color, rather heavy, moderately strong, It is excellent for furniture and interior
close grained.
finishing
Some
and can be stained to imitate mahogany. members are valuable for their prussic acid con-
of the
This may, however, be a source of danger, for children been have poisoned by eating the seeds of peaches and apricots, and when feed is scarce livestock will browse the leaves and twigs of wild cherry, a fact that has sometimes resulted in serious losses. tent.
31.
LEGUMINOSAE (FABACEAE) (PAPILIONACEAE).
This family
is
Pea Fanuly
one of the largest and most important.
close relationship of its
numerous members
is
shown by
The
their pea-
A TEXTBOOK OF SYSTEMATIC BOTANY
152
like flowers, pod-like fruits,
and compound
leaves.
They
fall
naturally into three subfamilies that some would call separate families, Mimosaceae, Caesalpinaceae, and Fabaceae or Papilionaceae. There are about 500 genera and 12,000 species, includ-
ing large trees, shrubs, vines, perennial herbs, and annuals, of world-wide distribution. It is therefore the second largest family of the dicotyledons.
Fossil remains indicate that
some woody members
of the
Leguminosae were
in existence during the latter part of the Cretaceous period, but most of the species, perhaps all the herbaceous ones, are products of the latter part of the Cenozoic era
and more recent
times.
Familiar examples are clovers (Trifolium L.), sweetpea (Lathyrus odoratus
Familiar Examples.
(Medicago saliva garden pea (Pisum sativum
spp.), alfalfa L.),
bean (Phaseolus hypogaea
L.),
spp.), lupine
soybean (Glycine Max Men*.), (Lupinus spp.), peanut (Arachis
L.),
black locust (Robinia Pseudo-acacia L.), and
many
others.
Stems and Roots,
The Leguminosae are predominantly hermany shrubs, woody vines, and trees.
baceous, but there are
The
member
of the family is the black locust, which not a reaches height of 80 feet and a diameter of 2 to 3 infrequently
largest
feet.
The
root system in the species that are perennial herbs is genThe roots of most species erally large and deep, e.g., in alfalfa. are commonly attacked by bacteria belonging to the genus
Rhizobium.
These enter through the root hairs and cause what
appears to be a diseased condition, in that certain cells are killed and inhabited by the bacteria, and other cells are stimulated to
abnormal multiplication that
results in the formation of
many
This localized injury is more than offset, tiny galls or nodules. the host receives from the bacteria, which the benefit however, by are
among
the few species that have the power of using the inert
nitrogen of the air and uniting it with other elements to compounds usable for food by the leguminous host.
form
Leaves. With few exceptions the leaves are compound, more often pinnate than palmate, and possessed of permanent stipules. Some of those leaves that appear to be simple are, in reality, unifoliolate.
The arrangement on the stem
genera, such as Lathyrus, Pisum, and
is
alternate.
In several
Vicia, the terminal leaflet
FAMILIES OF DICOTYLEDONS and sometimes others are reduced to a
tendril.
153
Movements
of
the leaflets or the leaves are fairly common. In Trifolium and Phaseolus, for example, the leaflets take a vertical position as darkness comes on. In the sensitive plants, Mimosa pudica L.
and Aeschynomene
virginica (L.) B.S.P., the petiole droops and the leaflets fold together when the latter are touched. In Desmodium gyrans DC., the telegraph plant, two lateral leaflets wave
up and down
periodically without external stimulus. The most common inflorescence
Inflorescences and Flowers. in the
Leguminosae
is
clovers, is shortened to
a raceme, which in some cases, as the such an extent that it is often spoken of as
a head.
FIG.
57.
A,
Vicia faba. Eichler;
The it is
flower
is
B, 13,
Lathyrus odoratus (Leguminosae). Bergen and Caldwell.)
more
after
quite characteristic in most species.
Generally
The
five or four
complete and hypogynous or perigynous.
sepals are
(A,
after
or less united.
The
five petals are unlike,
form-
The large ing an irregular flower with bilateral symmetry. standard. On either side two is called the are upper petal others, Below these, and more similar to each other, called the wings. or less enclosed by them, is the keel, which consists of two united In Amorpha the wings and petals, the others being distinct. keel are wanting, and in several species of Lcspedeza some of the There are generally ten stamens, which flowers are apetalous. in most species have their filaments united into one or two series.
A
The
pistil
considerable
for
insect
contains a single carpel with a superior ovary. of species show highly specialized devices
number
pollination.
In
approaches the Orchidaceae.
this
respect
the
family
almost
A TEXTBOOK OF SYSTEMATIC BOTANY
154 Fruits
and Seeds.
often called a legume.
Each flower develops a single true pod, Commonly the pod is dehiscent, but not
infrequently it develops into a special indehiscent hooked structure for seed distribution by animals. In Glycyrrhiza the pod short and unsegmented and bears well-developed hooks. In Desmodium, Iledysarum, and other genera of the same tribe the pods are divided transversely into easily separated segments covered with very fine hooks, and contributing to that hetero-
is
geneous group of fruits known as 'beggars' lice.' In Medicago the pods are small, spirally coiled, and either hooked or reticu-
The peanut
lated.
way.
As soon
(Arachis hypogaea L.) fruits in a very special as the flowers in the axils of the lower leaves are
fertilized they lose their petals and the peduncle turns downward, When thus buried it develops forcing the ovary into the soft soil. into the well-known peanut. If it fails to get buried because it
started too far above ground or the ground was too hard, the ovary withers and dies. The seeds of Papilionaceae contain a
no endosperm. Economic Significance. The Leguminosae rank second only to Gramineae in value to mankind. Probably a wider range of useMuch signififulness is found here than in any other family. cance lies in the fact that the Leguminosae are highly nitrogenous large curved embryo, with little or
For this reason they supplement well the foods and feeds obtained from the Gramineae, which are largely of a carbohydrate nature. The special food value of peas and in all their tissues.
beans
is
well
known, and the
tent of peanuts
make them
fine flavor
and
usable in
many
and protein conforms. No other
oil
plant except timothy yields so much hay as clover and alfalfa, and the pasture value of the legumes ranks above all others except
the grasses.
but for
Even
oil
The soybean
is
and raw material
grown extensively not only
for food
for plastics.
the legumes were wholly unpalatable, they would be extensively raised, however, because of their value to the soil. if
known that crops of this character other crops impoverish it. The explanaalthough 152. The decaying roots and stubble has been on tion given page For centuries
enrich the
it
has been
soil
bring much available nitrogen into the soil even though the stems and leaves are removed for hay. It is indeed rare good fortune that after the harvesting of an unusually valuable crop, such as clover or alfalfa, the land is left in much better condition for
FAMILIES OF DICOTYLEDONS
155
Man's benefit by the alliance between leguminous and the bacteria that inhabit their roots is incalculable. plants As a source of honey no other family compares with the Papilionaceae indeed in many states the yield from this family
other crops.
Flu. oo. uxyrropis i^amoem ^ijeguiiiuioMauj. plant is found in the open country from the Minnesota. (One-half natural size.)
exceeds that from
all
vv
other families combined.
and sweetclover greatest honey producers, and the quality alsike
clovers,
alfalfa,
uite or sienuuss
iui;u.
x ins
Rocky Mountains eastward
In white and
we have
In esthetic value this family ranks high.
is
to
four of the
of the best. It includes
myriads
A TEXTBOOK OF SYSTEMATIC
156
of beautiful wild flowers,
BOTANY
and sweetpeas and black locust
illus-
trate the cultivated forms.
From no other family are so many official drugs obtained. These include licorice, hematoxylin, tragacanth, senna, and physostigmine.
Two
important groups of stock poisoning plants are found in
this family, viz., the locoes
and the
lupines.
The
locoes include
Oxytropis Lamberti Pursh and a few species of Astragalus, notably
59. Lupinus sericeus (.Leguminosae) species, are found at nearly all altitudes United States. (One-fourth natural size.) Jb'ia.
.
many
A. mollissimus Torr.
unknown, and for
The lupines, oi which there arc throughout the western half of the
The poisonous
principle in these plants is are evident only after continuous feeding Loco poisoning causes heavy losses among
its effects
weeks or months.
and goats. There is increasing evidence, in domestic animals are erroneously that other maladies however, attributed to loco weeds. The lupines cause acute poisoning, horses, cattle, sheep,
in sheep. The poisonous principle has not been but losses are mostly from eating young pods conthe isolated, The mature pods are so freely dehiscent that ripe taining seeds. seeds rarely are eaten in quantity.
especially
FAMILIES OF DICOTYLEDONS
157
For so large a family, the Leguminosae are remarkably free from members that are classed as noxious weeds. This is in part because some that have the persistent habit of weeds are so freely eaten by livestock that they are thought of as forage plants In many places white, alsike, and sweet
rather than weeds.
' ' clovers abound, but although plants out of place they are not classified as weeds. few, such as wild licorice or buffalo bur (Glycyrrhiza lepidota Pursh), are obnoxious.
A
32.
SAXIFRAGACEAE.
Saxifrage Family
The family Saxifragaceae is a somewhat variable one, be made to include the Grossulariaceae as one of
if it
Without the currants and
FIG. 60.
especially its tribes.
gooseberries, as here considered,
it
Saxifraga granulata (Saxifragaceae). A, longitudinal section of flower. J5, floral diagram (A, after Warming; B, after Eichler.)
contains about 75 genera and 800 species, found chiefly in temperate zones and even extending into the arctic regions.
Familiar Examples. The saxifrages (Saxifraga spp.), hydrangea (Hydrangea spp.), and syringa or mockorange (Phttadelphus spp.) are among the best known examples. Stems and Roots. The members of this family are mostly There is a perennial herbs or shrubs, but a very few are trees. considerable tendency to vegetative propagation through rootstocks, runners,
Leaves. spiral,
The
and
bulbils.
leaves are quite variable.
simple, exstipulate, all these characters.
They are mostly and deciduous, but exceptions are
found in
In the herbaceous forms there
is
a
tendency to produce masses of basal leaves, with slender, leafless stems. Inflorescences and Flowers. eral
There
tendency in the inflorescence.
The
no uniformity or genflowers are mostly bisex-
is
A TEXTBOOK OF SYSTEMATIC BOTANY
158
and regular. The typical flower is 5-merous, but the carpels are often reduced, two being a common number. They are separate or loosely united. The stamen number is often twice ual
that of the petals, which are usually five but are lacking in a few
The insertion is usually hypogynous or perigynous, but species. every gradation between may be found. Fruits and Seeds. The fruit is generally a capsule or follicle, producing numerous seeds with abundant endosperm and a straight embryo.
Economic
Significance.
Except for a few ornamental plants,
Most of the species are unpalatable to livestock and sparsely produced. It is of considerable botanical interest because of its plasticity and consethe family
is
of
little
importance.
quent variability. 33.
The
GROSSULARIACEAE.
Gooseberry Family
gooseberries and currants constitute a rather clear-cut
family of
1
genus and about 130 species. The family is closely and by some authorities is included
related to the Saxifragaceae
with them. Familiar Examples. Currants and gooseberries (Ribes spp.), both wild and cultivated, are the only examples of the family. Stems and Roots. The representatives of this family are all shrubs, rather small, mostly from 3 to 8 feet high, in thick clumps. Nearly all species of gooseberries are armed with spines that are
extensions or protrusions of the cortex. The few strong spines ' ' at the nodes may be supplemented by weaker ones, prickles,
on the internodes. Leaves. The leaves are simple, serrate or dentate, and usually with about five lobes. They are alternate and generally longStipules are usually absent or, if present, are reduced petioled. to slight margins on the bases of the petioles. Inflorescences and Flowers. The typical inflorescence is an axillary raceme that is usually pendulous and sometimes reduced The flower is small, regular, and bisexto three or fewer flowers. ual. It is epigynous, or nearly so, with the receptacle extending ' to form a calyx tube' adherent to the ovary. This hypanthiuin, as it is called, continues in a circular ridge above the
FAMILIES OF DICOTYLEDONS
159
attachment to the ovary, and to this the colored sepals, the tiny The sepals, petals, and petals, and the stamens are attached. stamens are five in number, or rarely four. The pistil is inferior and bicarpellate, with two styles, which are sometimes united,
and two stigmas. Fruits and Seeds.
The pistil with grows into a very juicy berry, the wall oped from the surrounding receptacle.
its
of
adherent calyx tube
which
is
largely devel-
It contains several seeds
B IMG.
61.
and
in
is
B, Ribes aureum (Grossulariaceue). Sargent; B, after Robbins.)
A, Ribes rubrum.
some small and Economic
known
is
for their richly flavored,
grown
after
covered with minute spines. The embryo straight with abundant endosperm. Currants and gooseberries are well Significance.
species
strongly acid berries, which of the wild species are
have become a staple product. Some edible, but others have a disagreeable are
(.4,
flavor.
Certain species
for their profuse yellow or red flowers
and graceful
form. 34.
ONAGRACEAE.
Eveningprimrose Family
CA4 Co 4 S 8 P There are about 38 genera and 470 species, rather widely distributed, but most abundant in the subtropical portions of the Western Hemisphere.
A TEXTBOOK OF SYSTEMATIC BOTANY
160
Familiar Examples. Fuchsia (Fuchsia spp.), eveningprimrose (Oenothera spp.), and willowherb or fireweed (Epilobium angusti*folium L.) are well-known examples of this family. Stems and Roots. The Onagraceae are nearly all annual herbs
with a few biennials and occasional shrubby forms. Leaves. The leaves may be alternate or opposite and are simple and usually entire or nearly so, with stipules reduced to small glands or absent.
FIG. 62.
Oenothera biennis (Onagraceae)
Inflorescences and Flowers. solitary,
and
The
.
(From Bntton and Brown.)
flowers are often very large, They are bisex-
axillary, or borne in racemes.
and mostly regular and 4-merous, although the number of The sepals sepals, petals, and stamens varies from two to nine. are borne on a tube that is adherent at its base to the ovary and The distinct petals and sepals are often extends far above it. The pistil is composed inserted in the throat of the calyx tube. Its ovary is inferior or of two to six carpels, generally four. nearly so, and the style is often very long to reach the length of ual,
the calyx tube.
FA MILIES OF DICOT YLEDONK
I (> 1
and Seeds. The fruit is generally a capsule containing many seeds, which are without endosperm and contain a straight Fruits
or nearly straight embryo. In Epilobium the seeds bear a tuft of at one end, and these effectively aid in seed long silky hairs distribution.
Economic Significance. As a rule the Onagraceae are unpalatable to livestock, but the fireweeds are an exception and are valuable forage plants where available. They are also important plants, and in burned-over areas they often spring up in Many beautiful wild and cultivated plants great abundance. belong to this family. These include the eveningprimroses,
honey
fuchsias,
and
Clarkias. 36.
CUCURBITACEAE.
Gourd Family
p(i-J)
The Cucurbitaceae are essentially tropical and subtropical. hard for those who live in the northern United States to realize that there are about 100 genera and 800 species. Beyond It is
the Canadian border only a few species can be grown out of doors at all. Familiar Examples. Familiar examples are pumpkin (Cucurbita Pepo L.), squash (Cucurbita spp.), cucumber (Cucumis sativus L.), muskmelon or cantaloup (Cucumis Melo L.), watermelon (Citrullus vulgaris Schrad.), and wild cucumber or balsamapple (Echinocystis lobata (Michx.) T. and G.). Stems and Roots. The Cucurbitaceae are succulent, trailing The or decumbent vines, usually climbing by means of tendrils. stems of most species are hollow and live-angled with five cor-
responding bicollateral bundles. Leaves. The leaves are simple, but often deeply cleft, sometimes compound, usually exstipulate, large, and long-petioled. The petioles are often hollow. The arrangement on the stem is alternate. Concerning the morphology of the tendrils there is
much
difference of opinion. By some they are believed to be are leaves and the main portion or their branches that leaves, It others they are considered bracteoles. are and in Kedrostis spinosa they certain that stipules,
stem.
By
that in different genera they are of different origin.
is it
almost may be
A TEXTBOOK OF SYSTEMATIC BOTANY
162
Inflorescences and Flowers. in
the
axils,
The
flowers are usually solitary
but in the small-flowered species they
racemose or paniculate.
They
are unisexual
and often
may
be
dioecious.
In structure the flowers are quite characteristic. They are 5-merous, but with the pistil tricarpellate by reduction, and the stamens united into two pairs, accompanied by a single one.
The
filaments are short,
and the anthers long and slender but
FIG. 63. Cucurbita Pepo (Cueurbitaceae). Staminate and pistillate flowers with portion of corolla removed to show pistils and stamens. (One-half natural size.)
The style is short, folded or twisted into a compact mass. surmounted by a broad three-lobed stigma. The fruit is a pepo or gourd, rarely a capFruits and Seeds. of often sule, huge size; indeed, the largest of all fruits are found in this family.
The
seeds are numerous, generally large
and with no endosperm.
The embryo is
and
flat,
straight, with large, oily
cotyledons.
Economic Significance. The Cueurbitaceae have long played an important part in the affairs of mankind. Gourds of various shapes and sizes have been extensively used as primitive vessels
FAMILIES OF DICOTYLEDONS and
utensils.
The food
163
value, delicious flavor,
and abundant
production of the fruits have given them a prominent place. In addition to the familiar pumpkins, squashes, and melons, numerous other kinds are found in the tropics. To some extent, wild
cucumber and other vines are grown on
trellises for
ornamental
purposes. 36.
CACTACEAE. CA
to
Co
Cactus Family
S
About 100 genera and 1,000 species, restricted almost exclusively North and South America and most numerous in Mexico and
Central America.
Only one genus, Rhipsalis, is native to the Eastern Hemisphere. This is composed of epiphytes and is found in the tropics of Asia and Africa. The cacti are typically xerophytic and tropical but extend through the semiarid region of the west into southern Canada. Familiar Examples. Few cacti grow wild in the United States except in the far west, where the prickly pear (Opuntia spp.) is a common desert plant, and in the extreme southwest where many species are abundant. Nightblooming-cereus (Hyloccreus undatus Britt. and Rose) is often grown in dooryards, and crabcactus (Zygocactus truncatus Schum.), rattail cactus (Aporocactus flagelliformis Lem.), and many other species are in greenhouses and conservatories.
commonly found
Stems and Roots. Cactus stems are peculiar in appearance. are thick and fleshy, and while some grow 50 to 60 feet high
They
they can hardly be called shrubs or trees because of their texture. They are subglobose to cylindrical or flattened and most of them have prominent vertical ridges. Almost invariably they are spiny, sometimes extremely so, the spines growing from rounded cushions or tubercles composed of a combination of leaf base and
rudimentary branch. In many cases at least, the larger spines, and perhaps all, should be looked upon as specialized leaf parts. The root system is small and shallow for xerophytic plants of their size.
Leaves. Cacti are commonly described as leafless, the leaves being reduced to spines as stated above. In Opuntia a few small
awl-shaped leaves develop and
fall
when very young.
The
func-
A TEXTBOOK OF SYSTEMATIC BOTANY
164
tion of photosynthesis
Two
tropical genera
is
assumed by the dark-green stems.
show a mesophytic
structure, with slender
branches and broad simple leaves. Inflorescences and Flowers. The flowers are solitary, large, and showy. Generally they are regular or nearly so, but in some species the sepals are petaloid, or the petals sepaloid,
Opuntia Tuna (Cactaceae). A, portion of stem with bud, flower, C, single bristle. D, longitudinal section of B, cluster of spines. E, longitudinal section of fruit. F, seed (external). G, seed (internal).
FIG. 64.
and
fruit.
flower.
(After Rendle.)
making the two intergrading or indistinguishable. Perianth segments and stamens are generally numerous with epigynous insertion on the inferior ovary. The pistil is composed of several closely united carpels with one seed chamber.
Fruits berry.
embryo
and Seeds.
The
The fruit
is
a rather compact, many-seeded
seeds contain endosperm in varying amounts. varies from straight to semicircular.
The
FAMILIES OF DICOTYLEDONS Economic
165
The Cactaceae are of especial because of their extreme adaptation to xero-
Significance.
scientific interest
phytic conditions. They also have considerable economic importance. Their peculiar forms and gorgeous flowers have been given some recognition in the greenhouse, and the traveler in the American tropics is impressed with their adaptability to their environment.
The
use of cacti for rock gardens and plant-
ing under unusual conditions has
become quite extensive, and have been formed for their study and promotion. In Mexico cacti are sometimes grown for hedges. The fruits of some species are sweet and of good flavor, but their use is rather local. That the stems of some are nutritious is well established, but their compact form, vicious spines, and sometimes disagreeable taste have given them general immunity from consumption by societies
livestock.
Even that
recent introduction, the spineless cactus,
is
but a partial success. 37.
VITACEAE.
Grape Family
The grape family contains only about 10 genera and 500 They are widely distributed in temperate and sub-
species.
tropical regions.
Familiar
Examples.
Grape
(Vitis
spp.),
Virginia
creeper
(Parthenocissus quinquefolia (L.) Planch.), and Boston ivy (P. tricuspidata Planch.) are well-known examples of this family.
Stems and Roots. The Vitaceae are mostly vines, climbing by tendrils or by adventitious roots. The tendrils have a special morphological interest. They are borne at the nodes, opposite the leaves, and it is held on good authority that each represents the tip of the main shoot that has been pushed aside by the growth of a lateral bud at its base. In some species the tendrils
develop adhesive disks at their tips. A few tropical species are shrubs or small trees. The nodes are enlarged and the vines and The grape, especially, contains tendrils are tough and strong.
an abundance
of watery juice. Leaves. The leaves may be simple as in the grape, or they may be compound as in the Virginia creeper. They are petiolate with deciduous stipules and an alternate arrangement. Inflorescences and Flowers. The flowers are usually borne in panicles or cymes, which take the place of tendrils opposite the
A TEXTBOOK OF SYSTEMATIC BOTANY
166
leaves at certain nodes.
They
are small
and
either bisexual or
The calyx is four or five unisexual, in some species dioecious. toothed or reduced to an inconspicuous ring. The petals are of the same number, greenish in color, and generally fall as soon as the flower opens. There are four or five stamens, always opposite the petals, and a bicarpellate pistil, which is more or less
embedded
in a circular disk.
FIG. 65.
Fruits
Vitis (Vitaeeae).
and Seeds.
The
Partly opened flower.
fruit is
(After Robbins.)
a berry, well illustrated by the
The
seed contains oily endosperm and a small embryo. grape. Economic Significance. Grapes are extensively raised the
world over in all but the colder climates. Their use for food and wine goes back to the dawn of civilization, and much attention has been given to the development of varieties especially suited to the different uses. Vast quantities are dried into raisins, and the so-called dried currants are in reality made from certain for
varieties of tiny grapes.
In the east, middle west, and south the Vitaceae furnish the
FAMILIES OF DICOTYLEDONS
167
best of our climbing woody vines, some species having the very desirable feature of clinging to brick or stone buildings by short tendrils with disk-like ends or
need of brilliant
trellises.
autumn 38.
They
by
are
aerial roots,
made more
thus eliminating the attractive by their
colorings.
LORANTHACEAE.
Mistletoe Family
Co2~3 p(l72)-0
The
mistletoe family consists of about 21 genera and 500 spemostly tropical and subtropical, but a few found in temperate climates. Nearly all are parasitic on trees and shrubs. Only two genera and nine species are found in the United States and the following account is restricted to them. Familiar Examples. American-mistletoe (Phorandendron spp.) cies,
and small
or lesser mistletoe (Arceuthobium spp.) are the best of this family.
known examples
Our mistletoes are small, perennial, usually that grow as parasites on various trees. In shrubby plants The branching is dichotofrom 1 to 8 inches. length they vary Stems and Roots.
mous.
The
root takes the form of a haustorium that peneand sapwood of the host and from this source
trates the bark
obtains a part or all of the nourishment required by the plant. attacks chiefly angiosperms, such as poplars,
Phoradendron
willows, oaks, arid acacia, while Arceuthobium attacks gymnosperms, such as pine, larch, and Douglasfir. Leaves. The mistletoes are evergreen, and the larger forms are sometimes so abundant in a tree that they give it a leafy
appearance during the winter. The leaves are opposite and In Phoradendron they are about 1 inch entire, without stipules. with a pale-green color. half as and They are therebroad, long fore able to contribute something to the nourishment of the In Arceuthobium they are reduced to functionless scales, plant.
and the plant
is
strictly parasitic.
Inflorescences and Flowers. The flowers are solitary or few in the axils of the leaves. They are unisexual and dioecious,
and apetalous, with an inferior ovary. Fruits and Seeds. The fruit is commonly called a berry, but is morphologically a tiny one- to three-seeded pome, the fleshy
regular,
it
a 68
A TEXTBOOK OF SYSTEMATIC
BOTANY
This outer covering becomes receptacle covering the ovary. the beaks of the birds that have viscid, enabling it to adhere to
attempted to eat the fruits and to the feet of birds and squirrels that happen to have run over them. They are thus carried to other branches where they adhere with sufficient strength to enable the germinating seed to penetrate the bark. contain endosperm and the embryo is straight.
The
seeds
B FIG. 66. Phoradendron Wattii (Loranthaceae). A, staminate spikes. B, (7, petal with stamen. J5, pistillate spikes. E, single single staminate spike. F, longitudinal section of fruit. pistillate spike. (After Rendlc.)
The Loranthaceae are of no value Significance. as of except objects curiosity, arid of sentiment in the case of the English mistletoe. They do some damage by distorting their Economic
hosts at the point of attachment. 39.
ACERACEAE.
Maplo Family
Q A 5(4-12) Co O-5(-12)gO-12pO-
The maple family is a small one, containing only 2 genera and about 100 species. They are mostly confined to the North Temperate Zone and are especially prevalent in the eastern half of the United States. Like so many of our trees, their ancestry can be traced back to the Cretaceous period. Their place of origin appears to have been northen Canada or Greenland. The Glacial epoch greatly reduced the area covered by the maples and nearly
FAMILIES OF DICOTYLEDONS
169
exterminated them from northern and central Europe, but most As a result we often find species survived in favored localities. the same species in restricted spots on both continents of the Northern Hemisphere, with thousands of miles intervening. Occasionally they make nearly solid forests, but more often they are mixed with trees of other families. Familiar Examples. The maples (Acer spp.) and the box(^4. Ncgundo L.) are examples of this family. Stems and Roots. Nearly all members of the family are trees, some of them more than 100 feet high and 3 to 4 feet in diameter. A few species are shrubs. In forests the trunks of most species
elder
are straight, with the lower half free from branches. Standing alone, the trees branch widely and are nearly as broad as high. are rather slow in growing but long-lived. prominent and protected by large scales.
They
Leaves.
The
elder, pinnately
The buds
are
leaves are broad, variously cleft, or, in the boxThey are petiolate, exstipulate, and
compound.
opposite.
Inflorescences and Flowers.
The
flowers are borne in small
which take the form
racemes or cymes. Most maples are polygamous, the same inflorescence bearing both bisexual and In bisexual unisexual flowers. The box elder is dioecious. axillary
clusters,
They may be
of
either bisexual or unisexual.
flowers there are generally five distinct sepals, five small, dis-
stamens, and one bicarpellate pistil with two styles and a superior ovary. Fruits and Seeds. The fruit is a characteristic samara with one wing, each flower producing a pair, loosely attached to each other at the base, with wings diverging. These are the wellknown 'keys.' The embryo is curved or crumpled, and there is
tinct, regular petals, eight
usually no endosperm.
Economic
The maples are among our most The lumber is cut to the extent of a billion
Significance.
valuable forest trees.
board feet annually in the United States.
and some
and
It is exceedingly
varieties or individuals
close-grained, hard, strong, develop the beautiful bird's-eye grain so much prized for furniWith the exception of oak no ture and musical instruments.
other
wood
is
used so
much
for
implements and hardwood
floors.
For fuel it is famous, and the maple backlog for the fireplace has become celebrated throughout the east. The fertilizer value of
170
A TEXTBOOK OF SYSTEMATIC BOTANY
Acer saccharum (Aceraceae). 1, staminate inflorescences. 2 and staminate flower. 4, pistillate inflorescence. 5, pistillate flower. 6, bisexual flower. 9, twig with leaf scars and 8, longitudinal section of fruits. 7, fruits. buds. (After Illick.) FIG. 67.
3,
FAMILIES OF DICOTYLEDONS
171
the leaves and the ashes has long been recognized. For ornamental planting the maple trees will hold their own with the best. Nor must we forget the delicious maple sugar and syrup obtained
from the sap of Acer saccharum Marsh. The maple family having many good traits and no bad ones.
ANACARDIACEAE.
40.
is
one
Cashew Family
This family has a wide distribution in temperate and tropical There are about 65 genera and 500 species. Familiar Examples. The best known examples growing in the United States are the sumacs (Rhus spp.) and several poisonous regions.
species of
Rhus variously known
as poisonivy, poisonoak, poison-
sumac, and poisonelder. Imported from the tropics arc pistachio nuts (Pistachio, vera L.) and cashew nuts (Anacardium occidentalelj.).
Stems and Roots.
This is a family of trees, shrubs, and woody with bark. resinous vines Leaves. The leaves are generally alternate and either simple A few species are evergreen. or compound. Inflorescences and Flowers. Most species bear their flowers in
These flowers are usually small, bisexual, and irregular, three to seven petals commonly five with stamens of having The number of carpels the same number or twice as many. panicles.
varies
and
from one to
five.
The
receptacle
is
conspicuously broad
fleshy.
Fruits
and Seeds.
but in some
Economic
it is
The fruit
of
most Anacardiaceae
is
a drupe,
a few-seeded berry.
Significance.
The
family that is of significance to fruits or seeds of a considerable
proportion of species of this
man
is
number
relatively large.
The
are highly prized for cashew nuts and the
These include the pistachio and mango. Because of their shapeliness and colored foliage and A few, fruits, many are extensively grown as ornamentals. food.
including poisonivy, are skin irritants. 41.
JUGLANDACEAE.
Walnut Family
In the Juglandaceae we have a small family of fine large trees. There are but 6 genera and 35 species. In all likelihood they are
A TEXTBOOK OF SYSTEMATIC BOTANY
172
not genetically close to the other Amentiferae, e.g., the birches and the poplars. Apparently the Juglandaceae were once more abundant than now. Their remains are found in Cretaceous rocks, and throughout the most of the Cenozoic era they were widely distributed over the Northern Hemisphere, with the exception of the arctic The frigid climate that generally prevailed in the North regions.
Temperate Zone during the Pleistocene epoch exterminated them except in favored localities. Europe lost all of her hickories and nearly all of her walnuts, the survivors beirig restricted to the eastern Mediterranean region. Familiar Examples. Well-known examples of the Juglandaceae are walnuts (Juglans nigra L. and J. regia L.), butternut (J. cinerea L.),
hickories (Carya spp.),
and pecan (Carya Pecan
Aschers. and Graebn.). Stems and Roots. The existing members of thfc Juglandaceae are all trees, often of considerable size. The pecan and the
black walnut grow to a height of 150 feet and a diameter of 6
When somewhat
crowded, they have straight, smooth half free the lower from branches. Standing alone, they trunks, are widely branching and of striking appearance. The young bark is glandular and somewhat aromatic, and the pith in walnut and butternut is diaphragmed, i.e., filled with thin, hard, horifeet.
zontal partitions set at close intervals, in longitudinal section
appearing like a ladder. In most species two or three buds may be fouitd above each leaf. The lowest is in the axil of the leaf, or slightly above, and the others are superposed in a row, with small intervals between.
The buds
are large and well protected by stout scales, which are The leaf scars are v^ry large and often densely pubescent.
conspicuous.
The leaves are odd-pinnately compound and very some species. In black walnut and butternut, which commonly have thirteen to nineteen leaflets, they are as much The leaflets vary from as 2 feet long and very handsome. lanceolate to ovate, with finely serrate margins, and have a viscid aromatic pubescence, especially on the lower surface. Leaves.
large in
The arrangement on
the stem is alternate. and Flowers. The flowers Inflorescences
in the Juglandaceae
are unisexual,^ the staminate in pendulous aments,
and the
FAMILIES OF DICOTYLEDONS
FIG.
68.
Juglans cinerea
(
Juglandaceae)
.
1,
173
branch with staminate and
3, staminate flower. pistillate flowers. 2, leaflet. 4, pistillate flower. 5, fruits. 6, twig. 7, longitudinal section of twig. 8, leaf scar and superposed
buds.
9,
nut with husk removed.
(After Illick.)
10 and 11, terminal buds.
12, lateral buds.
A TEXTBOOK OF SYSTEMATIC BOTANY
174
few in a group.
pistillate solitary or
same
Both kinds are borne on the
tree.
The staminate aments are borne just above the leaf scars of the previous season. They may be either single or in clusters of two or three, and are from 3 to 5 inches long. Each ament produces many staminate flowers. Each flower consists of a group of several pollen sacs, surrounded in most cases by a two- to sixlobed perianth. This flower is set in the axil of a bract with a small bracteole on either side. Occasionally a rudimentary pistil is borne in the staminate flower. The pistillate flowers are borne at the tips of the twigs. Each consists of a bicarpellate pistil with a calyx of four lobes (sometimes three or
ovary
five),
is inferior,
The
styles.
and often with as many tiny petals. The >so, with one ovule and two stigmatic
or nearly
pistillate flower, like the staminate, is set in
of a bract with
two
lateral bractcoles.
It is
the axil not ready for fertili-
zation until after the pollen is shed. It will be noted that such flowers are far from primitive but show a considerable degree of specialization. Fruits
and
in
The fruit is a nut, or, in reality, a sort of thick outer wall or husk, is tough and leathery It appears to be formed by a species dehiscent.
and Seeds.
The
dry drupe.
some
The inner shell or perifusion of bract, bracteoles, and perianth. carp is exceedingly hard. It consists of the matured ovary wall.
The nut
contains a single seed with two large, lobed, and con-
volute cotyledons and no endosperm. In certain genera, no longer found in the United States, notably Engelhardtia, the fruit is small, with large wings, a samara.
Economic Significance. In proportion to the number of individuals the Juglandaceae are of great importance. The fruits of the walnut, butternut, pecan, and some species of hickory are very highly prized and grown in considerable abundance.
The wood
walnut is so desirable for furniture, interior has been cut almost to extermination. It finishing, etc., is rather dark, even-grained, strong, easy to work, and holds its shape well. The wood of the butternut is softer and weaker and yet of fair quality. In hickory we have one of the greatest of black
that
it
of all woods for certain purposes. It is light in color, very closeand even-grained, and exceedingly strong, especially the second growth that has sprouted up from stumps and grown into small
FAMILIES OF DICOTYLEDON*
175
No other wood can replace it where extreme toughness required, as for hammer and axe handles, and spokes, shafts, The wood of the pecan is tongues, and other parts of wagons.
trees. is
intermediate in weight and strength between walnut and hickory. Unfortunately, the trees of this family have a very limited range. They are more abundant in the United States than elsewhere,
but here they are found only irregularly in the eastern and southThe demand has greatly exceeded the supply with the results that one would
eastern sections and on the Pacific coast.
expect.
Aside from their value for lumber and nuts, the walnut and butternut are highly desirable for ornamental trees, since their great spreading tops
by any other
and magnificent
foliage are hardly surpassed
trees. 42.
FAGACEAE.
Beech
or
Oak Family
PfcZ)
Members of the Fagaceae are familiar to nearly all who live in the vicinity of deciduous forests. There are G genera and about 350 species. They are earliest known from the Cretaceous rocks, and during most of the Cenozoic era they were abundant and While the Glacial epoch reduced them considerably, they are still numerous throughout the North Temperate Zone with some extensions into the South Temperate. cosmopolitan.
Familiar Examples. Familiar examples of the Fagaceae are beech (Fagus grandifolia Ehr.), oak (Quercus spp.), and chestnut (Castanea spp.), but not the horsechestnut (Aesculus spp.), which belongs to another family (Sapindaceae) .
Stems and Roots. In each
All of the family are either trees or shrubs. of the three more important genera trees can be found
more than 100 feet high and 6 feet in diameter, and a few old monarchs greatly exceed this size. Where grown thickly in the forest the trees have straight, smooth, branchless trunks for half to three-fourths of their height.
open they form magnificent spreading being but a few feet from the ground.
The
somewhat
Growing
solitary in the
tops, the lowest branches
In the beech the older ones near the great trunks are exposed above the surface of the ground. The oaks are very deep-rooted forming almost a taproot in roots are
variable.
A TEXTBOOK OF SYSTEMATIC BOTANY
170
some
The
cases.
chestnuts are intermediate in depth of root
system. Leaves.
The
few
but generally toothed or
species,
leaves are alternate, simple, petiolate, entire in a cleft.
Where
stipules form,
they are fugacious. In Castanea and usually in Fagus the leaves are deciduous. In Castanopsis and Lithocarpus they are evergreen, while in Quercus both kinds are found in different species. Inflorescences and Flowers. with unisexual apetalous flowers. are in dense umbel-like clusters.
All
species
are
monoecious
In Fagus the staminate flowers In the other genera they arc
in aments, erect or pendulous, often large and abundant, giving the tree a beautiful appearance when in bloom. The pistillate flowers are solitary or two or three in a cluster.
The staminate
flowers are borne in deciduous bracts and cona small cluster of stamens in a cup-shaped, four- to seventoothed calyx. A rudimentary pistil is sometimes found with sist of
The pistillate flowers are three- to seven-carpellate many chambers and styles as carpels. There are one or
the stamens.
with as
two ovules
in each
The ovary calyx
that
chamber, but only one in each ovary develops. enclosed in a perigynous four- to eight-toothed occasionally includes rudimentary stamens also.
is
A
many-scaled involucre surrounds the base of each flower. Fruits and Seeds. In most species the fruit matures the first season, but in Castanopsis, Lithocarpus, and some species of Quercus not until the end of the second season. The fruit is a In nut, borne singly or in twos or threes, in a dense involucre. the oaks the involucre forms a rough basal cup. In beech, chestnut, and chinkapin it is a prickly bur entirely covering the fruit and opening by four valves at maturity. In the beech and chinkapin the nuts are angled. In the oak and chestnut they are rounded except that in the latter the compressed surfaces of the adjoining three are somewhat flattened. The seed is without endosperm, starchy, nutritious, and well flavored except in the oaks, where in
Economic
most
species
it is bitter.
The family Fagaceae is the most Significance. important of the woody angiosperms. The great abundance and high quality of the wood are well known. Probably more high-class furniture is made from oak than from all other kinds of lumber combined. It is extensively used for floors and interior work. In the days of wooden vessels it was the mainstay in ship-
FAMILIES OF DICOTYLEDONS
177
1, branch with staminate aments. Quercua prinoidea (Fagaceae) staminate flower. 3, pistillate flower. 4, fruiting branch. 5, acorn cup formed from the involucre. 6, fruit (acorn). 7, twig in winter condition. 8, leaf scar and lateral buds. (After Wick.)
Fio. 69.
2,
A TEXTBOOK OF SYSTEMATIC BOTANY
178 building.
wood
Its sturdiness
is
a tradition the world over.
The
heavy and strong as that of most of the oaks, much more even-grained, and almost impossible to split. It is very resistant to the action of water and free from objectionable taste, hence its extensive use for household utensils, spoons, Its use in shipbuilding has been second plates, tubs, vats, etc. Chestnut yields a lighter wood not well only to that of oak. suited to building purposes where exposed to the weather, on account of checking and warping, but of great value for fence posts, mine props, telephone and telegraph poles, and railroad The devastation caused by the chestnut blight has been ties. of
beech
is
as
one of the greatest tragedies of the eastern forests. All members of the family tire excellent for fuel and are extenThe oak and beech are rather sively used for this purpose. but the chestnut grows rapidly, especially the slow-growing, second growth sprouting up from stumps. Throughout all the history of Europe the beech and oak have played a conspicuous part in the traditions, sentiment, and The oak has long been symbolic superstitions of the people. In all regions where these trees will of protective strength. grow they rank among the first for ornamental planting. The oaks, especially, show a marked tendency to produce cork in the bark. This development reaches its climax in the cork oak (Qucrcus Suber L.), from which it is removed in great The bark of other oaks is extensively sheets for technical use. used in tanning leather. The nuts of beech, chinkapin, and chestnut are of the finest quality, and a few species of oak, especially Quercus Michauxii Few species of nuts are produced Nutt., produce edible acorns. In crowded forests the yield in such quantities as the chestnut. is low, but where the trees are scattered they bear heavily. This nut is so abundant and so desirable as a food product that in some Certain parts of Europe it is even dried and ground into flour. Asiatic and cultivated varieties are much larger than the American species but inferior in flavor. Where beechnuts, chestnuts, and acorns are abundant, they are a valuable source of feed for swine; these animals eat the fruit of all species regardless of bitter flavors, and they can find them among fallen leaves where human beings would have little success.
FAMILIES OF DICOTYLEDONS 43.
BETULACEAE. n
The
birches
and

79
Birch Family
CACo
their relatives are well
known throughout
the
deciduous-forest regions of the country. There are 6 genera and about 80 species found mostly in the North Temperate Zone
but a few extending into the South Temperate Zone in the Andean The arctic birches of today are found as far north as any woody plants, but in the latitude of northern United States and central Europe they are at their best. Their earliest remains are from Cretaceous rocks, and throughout most of the Cenozoic era a considerable number of species flourished that are
region.
extinct. On the whole, however, they held their own through the Glacial epoch better than did most plants. Familiar Examples. The best known of the Betulaceae are birches (Betula spp.), alders (Alnus spp.), and hazelnut and filbert
now
(Corylus spp.). Stems and Roots.
The Betulaceae are all woody, varying in from the dwarf arctic birches to the yellow, black, and canoe birches, which are sometimes more than 100 feet high and 4 feet size
One of the conspicuous characters of the family is the periderm, the thin corky outside layer of the bark that in the The birches especially can be peeled off like a sheet of paper. color varies from very dark brown through red-brown and yellow
in diameter.
The young shoots are slender, elastic, and tough, so much so that the quality of the birch rod of the schoolroom has become traditional. Terminal leaf buds are not formed at the close of the growing season (except in Alnus), and to almost snow-white.
the shoot continues its growth the next year through the activity of a lateral bud near the tip.
Leaves. The leaves are simple, serrate, and petiolate, with an alternate arrangement on the stem. In the unfolding bud they have stipules, but these fall off as the leaves expand. Inflorescences and Flowers. The flowers are unisexual and usually monoecious. Both kinds are borne in aments that are well begun the season before flowering and rest over winter unprotected by bud scales. Sometimes two or more grow from the same node.
The staminate aments, when expanded,
are
1^
to 4 inches
A TEXTBOOK OF SYSTEMATIC BOTANY
180
FIG.
1, branch with staminate and (Betulaceae) same, but more advanced stage. 3, fruit. 4, scale of staminate ament. 6 and 7, lateral buds and leaf scars. (After
Betula papyri/era
70.
pistillate flowers.
strobilus. Illick.)
5,
2,
.
FAMILIES OF DICOTYLEDONS
181
long and pendulous.
In the axil of each scale are one to three* three apparently being the typical number, which is reduced in some species. There may or may not be a calyx. If present, it consists of a four-, five-, or six-toothed shallow cup. flowers,
Petals are absent.
may be two
The
flowers adhere to the bracts
or four bracteoles
more or
less
and there
united with each bract
at its margins.
The pistillate aments are shorter than the staminate (generally a fraction of an inch), erect when young, but somewhat penduIn Corylus they are reduced to a few flowers. lous at maturity. Two or three flowers are borne in the axil of each scale. The calyx, if present, adheres to the ovary, making the latter inferior. The pistil is bicarpellate, with one or two styles and two stigmas. One or two ovules are found in each chamber of the ovary. In most species the ovules are immature at the time of pollination, and the pollen grains germinate and penetrate the styles where they
lie
dormant
for several weeks, until the ovules are ready for
fertilization.
In most of the Betulaceae the pistillate Fruits and Seeds. aments develop into woody cones, doubtfully homologous with the strobili of the gymnosperms. In these matured inflorescences are found seed-like fruits (nutlets), generally one to each scale. In many species they are winged either two lateral wings or a circular one.
In the hazelnut (Corylus) the fruits are larger, Yi to in diameter, nearly spherical, wingless, and borne in pairs.
%
*
nc h
Each nut is covered by a husk that grows over it from the base and extends an inch or so beyond the apex in the form of a tube. This husk consists of an involucre made up of two united bract-
The
lets.
surface
is
thickly set with
stiff,
sharp, protective
hairs.
Each fruit contains one seed with relatively large cotyledons and no endosperm. The embryo is straight. Economic Significance. Few families of woody dicotyledons are as important in northern and temperate countries as the Betulaceae.
The wood
of the larger birches is of high quality,
and even-grained.
hard, heavy, strong, to that of some of the maples.
It is
somewhat
When seasoned it
holds
similar
its
shape used very extensively for interior finishing, floors, furniture, and various small articles such as Indian clubs and well
and
is
A TEXTBOOK OF SYSTEMATIC BOTANY
182
other athletic goods, spools, and baskets. When suitably stained makes an excellent imitation of mahogany. For fuel birch is
it
hardly surpassed by any wood, and alder has been extensively used in the manufacture of charcoal and of black gunpowder. The bark of several species has been very widely used in basThese ketry, but the great utility of birch bark is for canoes. light, responsive crafts have for centuries been the chief means of navigation on the swift streams of northern United States and Canada. Extensively used by the Indians, who made them with remarkable skill, they made possible much of the exploration of the American continent by the early traders and missionaries. Thousands of them are still in use, notwithstanding the competition of the canvas canoes
made
The
in imitation of them.
generally used in their manufacture
tree
the canoe birch (Betula papyrifera Marsh.), the white tough bark of which can be peeled off in
is
large sheets.
The
inner bark of the birches
is
and
rich in starch
in
some
spe-
cies, e.g., sweet or black birch (Betula lenta L.), it is very palatable and has been extensively eaten in times of distress. There is no
better browse for livestock, deer, etc., than birch twigs, either with or without leaves. Hazelnuts and filberts, both being sold
under the
latter
name, are among the best nuts we have.
inexpensive imitation of bark.
The
oil
of wintergreen is extracted
A good, from the
named 'The Lady
of the Woods.' and Few, beauty. The white are on extensively grown public and private species, especially, their and reach supreme development in the cut-leaved grounds if
birch has been well
any, trees surpass
it
in grace
weeping birch, a horticultural variety 44.
of Betula alba L.
CORNACEAE. Dogwood
Family
P(O) Of the Cornaceae there are 10 genera but only about 115 species. These are found mostly in the North Temperate Zone, with a little extension into South America. There are indications that they originated in what is now northern Canada or Greenland and spread to all the continents of the Northern Hemisphere. Their lineage dates back to the Cretaceous period, but they have never been a conspicuous part of the earth's flora. At present they
FAMILIES OF DICOTYLEDONS are found scattered through forests banks of streams over a wide area.
of other trees
183
and along the
Familiar Examples.
Flowering dogwood (Cornus florida L.), dogwood (Cornus Nuttallii Aud.), the common smallflowered dogwood (Cornus spp.), blackgum (Nyssa sylvatica Marsh), and tupelo (Nyssa spp.) are representative examples. Stems and Roots. The Cornaceae are mostly shrubs, but the Pacific dogwood is a tree, sometimes (30 feet high and 1 Pacific
foot
diameter.
in
Several
species are conspicuous for the color of their bark, which is
green in some but deep red in The wood of the others. eastern flowering
exceedingly
hard
dogwood is and close
The pepperidge
grained.
or
sour-gum trees tend to become hollow as they grow older and are often inhabited bees,
by wild
hence the use of the term
'gum'
as a colloquial
name
for a beehive.
Leaves.
The
leaves
are
simple and usually entire, and exstipulate. petiolate,
Their arrangement is generally opposite.
Inflorescences and Flowers.
FIG. 71. Cornus NnttaUii (OoriiaA, flower cluster encircled by ceae). B, single flower. (7, petal-like bracts. cluster of fruits. (After Jepson).
The inflorescence is usually a cyme or a panicle, but it may be a head with four to six large The flowers are small, regular, and petaloid bracts at the base. mostly bisexual and 4-merous, except for the bicarpellate ovary. In the so-called flowering dogwood, insertion is epigynous. the inflorescence is practically a head of tiny flowers inside of a whorl of four, five, or six large, white or pink, showy bracts, which The whole effect is that of a are commonly mistaken for petals.
The
single flower 3 to 4 inches in diameter.
Fruits
and Seeds.
which at maturity
The
may
be
a small berry-like drupelet It contains red, white, blue, or green, fruit is
A TEXTBOOK OF SYSTEMATIC BOTANY
184
one or two seeds with copious endosperm.
The embryo
is
often
small.
Economic
In two respects the Cornaceae are The dogwoods are ornamental shrubs, some prized valuable. for their bright-red bark, which gives them a striking appearance through the winter when the leaves are gone, and some for the These ' false flowers,' large, showy, petal-like flower bracts. as they may be called, appear in the undergrowth of the forest early in the season and are of striking beauty, some of them Significance.
being 3 inches or more in diameter. The tupelo trees of southeastern United States yield a great abundance of nectar that
makes honey 46.
of a high quality.
UMBELLIFERAE (AMMIACEAE). 5
5
CA Co S
Carrot Family
5
[email protected]~ The family Umbelliferae is a rather large one, containing about 270 genera and 2,700 species. They are widely distributed but most abundant in the North Temperate Zone. Familiar Examples.
Familiar examples are carrot (Daucus
Carota var. saliva DC.), parsnip (Pastinaca saliva L.), parsley (Pelroselinum hortense Hoffm.), and celery (Apium graveolens L.). Stems and Roots. The Umbelliferae are herbaceous, with a
predominance of perennials, although biennials and annuals are numerous also. In many species the nodes are conspicuously Commonly the stems enlarged and the internodes are hollow.
The roots are large tap, fascicled, or are vertically ridged. Rootstocks are found in some and often fleshy. irregular species.
With few exceptions the leaves are pinnately comThe petiole is often swollen, often decompound. and pound even hollow at the base, and sheathing the stem. Stipules are The rare, and when present they are small or membranous. Leaves.
arrangement
is
alternate.
Inflorescences and Flowers.
As would be expected from the
name
of the family, the inflorescence is usually an umbel. It is reduced to a single flower in some species of Azorella and Hydro-
however, and forms a compact head in Eryngium. The and bisexual. They are 5-merous for the which is The order of developpistil, bicarpellate. except cotyle,
flowers are small, regular,
FAMILIES OF DICOTYLEDONS
185
ment of the floral organs is peculiar, viz. stamens, petals, sepals, and pistil. The calyx may be reduced to a few minute scales or to a narrow circular ridge. The insertion is epigynous. Fruits and Seeds. The fruit is characteristic of the family and is called a schizocarp. At the top, where the style was attached, is an elevation, the stylopodium, which is the remains of a necIn dehiscence the two carpels, called mericarps, separate, tary. the line of division being called the commissure. For a time :
- anther
rib
commissural side Fia. 72. Pastinaca sativa (Urn belli ferae). A, longitudinal section of flower. E, fruit. Z>, floral diagram. B, top view of same. C, dorsal view of mericarp. F, cross section of mericarp. (After Robbin8.)
after dehiscence each mericarp
hangs suspended by a slender
Each mericarp contains a single seed, stalk, the carpophore. which is adherent to it, with the result that the whole structure The fruit is variously marked with is commonly called a seed. ribs,
grooves, bristles,
generic and
specific
and
oil
tubes,
distinctions.
which are much used for seed has a hard oily
The
endosperm.
The Umbelliferae are important Significance. Of the vegetables, volatile oils, and drugs. chiefly for vegetables, the chief The bienmembers. are carrots, parsnips, and celery Economic
nial species store
much
food in fleshy taproots the
first
year of
186
A
TEXTHOOK UF SYSTEMAT1C BOTANY
IMG. 73. Cicala occidentalis (Umbclliferae). Water hemlock or water This common name applies to the various species of Cicuta, all of parsnip. which are probably poisonous from the presence of cicutoxin. They are widely distributed and grow chiefly in marshy places and along streams and ditches. (One-eighth natural size.)
their growth, and if these are grown a second season this food is used in fruiting. Volatile oils, resins, etc., are produced in glands in the bark, leaves, and fruits and give the plants their fragrance.
Caraway (Carum Carvi L.), dill (Anethum graveolens L.), and Anisum L.) are used for flavoring. Angelica,
anise (Pimpinella
FAMILIES OF DICOTYLEDONS carum
oil,
187
conium, asafetida, and numerous other medicinal
products are obtained from this family. The family Umbelliferae is one of the most important for forage Among the members worthy of mention are the angeliplants. cas (Angelica spp.), cowparsnip (Heracleum lanatum Michx.), wild parsley or carrot (Lcptotaenia spp.), and sweetcicely (Osmorrhiza spp.). Several species are poisonous. Most impor-
tant
among
these
is
waterhemlock, cowbane or poison parsnip
The fleshy roots of (Cicuta spp.), and conium (Conium spp.). these plants are very deadly to all kinds of livestock and have
many
times been fatal to man. The poisonous principle is an There is a popular belief that, if the common
alkaloid, cicutin.
garden parsnip escapes from cultivation, it becomes poisonous. This is an error based on wrong identification. It has been abundantly proven that parsnip run wild is harmless. 46.
RUBIACEAE.
~
'
Madder Family
'
P is a large family of some 350 genera and 4,500 species. species are found in the tropics and subtropics, but a considerable number grow in temperate zones.
This
Most
Familiar Examples.
In some cases we are familiar with the
These include bedstraw (Galium spp.), buttonbush (Cephalanthus occidcntalis L.), madder (Rubia tinctorum L.), capejasmine (Gardenia jasminoidcs Ellis), coffee (Coffea arabica L.), and quinine (Cinchona plants themselves, in others with their products.
officinalis
Hook.).
Stems and Roots. The family consists mostly of shrubs and small trees, with some vines and herbaceous plants. Inflorescences and Flowers. The flowers are usually solitary In most species they are regular, in or in small axillary clusters. a few slightly irregular, ovary inferior, carpels generally 2 to stamens 4 or 5. Fruits
5,
The leaves are simple and in most cases whorled. The stipules are often conspicuous and
and Seeds.
opposite or leaf-like.
Economic Significance. Some very important products come from the Rubiaceae. The two most important of these are
A TEXTBOOK OF SYSTEMATIC BOTANY
188
obtained from the fruits of the coffee tree, and quinine, ' obtained from the cinchona bark. The coffee beans' are seeds, two of which are produced inside each pulpy fruit. The alkaloid
coffee,
quinine, of which the bark sometimes contains as much as 10 per cent, is extracted by mechanical and chemical processes, after
which
it is
tant dye
easily purified. extracted.
A
is
From
jasmine or gardenia, are grown mild climates. 47.
the roots of
madder an impor-
number
of species, including capein greenhouses and out of doors in
CAPRIFOLIACEAE.
Honeysuckle Family s3
-5
or
CozEJO
P(O) This family consists of about 1 1 genera and 340 species, found mostly in the Northern Hemisphere. Familiar Examples. The honeysuckle (Lonicera spp.), elderberry (Sambucus spp.), snowberry or buckbrush (Symphoricarpos spp.), and twinflower (Linnaeaborealislu. andL. americana Forbes) are familiar examples. Steins and Roots. The Caprifoliaceae are predominantly shrubs with a few vines, trees, and herbs.
Leaves.
The leaves
are generally simple (pinnately
compound
In some species, e.g., in the Loniof the sessile pairs upper leaves have their bases united ceras, Stipules are usually absent, but present in (connate-perfoliate). Sambucus and a few other genera. A few, such as twinflower,
in
Sambucus) and
are evergreen. Inflorescences
opposite.
The predominant inflorescence be variously modified by suppression of may terminal (central) or marginal flowers, or by compounding, as in Sambucus. The flowers are bisexual, gamopetalous, and often They are primarily 5-merous, but the parts may be irregular. reduced to two, three, or four. The insertion is epigynous. Fruits and Seeds. The fruit is generally a berry, but sometimes a drupe or a capsule. The seed contains fleshy endosperm and a straight embryo. Economic Significance. The honeysuckle family r^nks very high for ornamentals shrubs, both cultivated and wild. Some of is
and Flowers.
a cyme, but this
the species of Sambucus and Symphoricarpos furnish considerable
FAMILIES OF DICOTYLEDONS browse for livestock.
189
Several species of Symphoricarpos are
important honey-producing plants. 48.
COMPOSITAE.
Composite
Family
g5or
CA-p Co
or
Coz
p( JU2) or
The Compositae
are generally rated as the largest and highest There are at least 850 genera and
of all the families of plants.
15,000 species. They are of world-wide distribution, and different members grow under every ecological condition where flower-
FIG. 74. Head of sunflower. A, longitudinal section of inflorescence showing ray flowers and tube flowers. The older tube flowers toward the margin are fertilized and withered while the younger ones at the center have not yet opened. B, external view of ray flower. C, interior of ray flower, showing absence of stamens and pistil. D, external view of tube flower. E, interior of tube flower showing petals, stamens, pistil, and ovule.
ing plants are found. Some authorities would divide this great family into three Ambrosiaceae, Cichoriaceae, and Compositaceae or Carduaceae.
Familiar
Examples. (Helianthus annuus L.), spp.),
lettuce
Familiar
examples
are
sunflower
aster (Aster spp.), goldenrod (Solidago (Lactuca saliva L.), dandelion (Taraxacum
Webber), ragweed (Ambrosia spp.), chrysanthemum (Chrysanthemum spp.), cocklebur (Xanthium spp.), Canada thistle (Cirsium arvense (L.) Scop.), yarrow (Achillea millefolium L.), and wormwood or sagebrush (Artemisia spp.). officinale
Stems and Roots.
The Compositae
are nearly all herbaceous, but a small proportion are shrubby, and in the tropics a few reach the stature of trees. Tubers are produced by a few species, e.g. t
A TEXTBOOK OF SYSTEMATIC BOTANY
190
Jerusalemartichoke (Helianthus tuberosus L.), and wild artichoke or Maximilian sunflower (H. Maximiliani Schrad.). Many species
have a milky
Leaves.
and
The
juice (latex).
leaves are mostly simple, alternately arranged,
exstipulate.
Eupatorium urticaefolium. White snakeroot. This plant is found woods and pastures throughout the eastern half of the United States. (One-
FIG. 75 in
half natural size.)
(After Hansen.)
Inflorescences and Flowers. The inflorescence is a head subtended by an involucre. It is so compact that the layman usually things it is a single flower. The flowers are varied, mostly bisexual, but frequently pistillate or neutral, i.e., with both sta-
mens and
In one pistils aborted, and occasionally staminate. head (discoid) the corolla is small and regular (tubular) in the flowers. In a second type (radiate) the central flowers
type of all
FAMILIES OF DICOTYLKUONti
191
are tubular, and those in the outer row are ligulate and generally In a third subfamily all the flowers are pistillate or neutral. ligulate.
The
reduced to
70.
is
scales, bristles,
entirely absent.
FK;.
epigynous and the calyx teeth are or a shallow cup, or they may be The corolla is five-toothed, the stamens usually
insertion
X'ltithium echinatum (Ambrosiaceae).
The cockleburs
are found
most coMiiiionlv in cultivated fields, waste places, and along the banks of streams where the burs have been deposited by the water. After the plants reach the height of a few inches, they cease to be poisonous. (One-third natural size.) five in number and connate, and the pistil bicarpellate, with one chamber and one ovule. Fruits and Seeds. The fruit is generally a simple achene, which may be naked or plumed from the development of the
pappus
(calyx).
endosperm.
The embryo
is
straight
and
thoro
is
no
TtiXTBOOK OF SYSTEMATIC BOTANY
192
Economic
Significance.
The Compositae cannot be rated
among the highest as a direct source of food for mankind, although lettuce, chicory, artichokes, and salsify make their contributions.
A
great
number
of species
have considerable forage
value, and the cultivated sunflower is excellent for ensilage in Poisonous regions where corn cannot be grown in quantity. members are not generally troublesome, although white snakeroot (Eupatorium urticaefolium Reich.), western sneeze weed (Dugaldia
FIG.
77.~Xanthium echinatum, Cocklebur. cotyledons
still
It is at this young stage, while the persist, that the plants are poisonous. (Natural size.)
Hoopesii (A. Gray) Rydb.), some of the goldenrods (Solidago spectabilis and S. concinna A. Nels.) are known to cause some
Of these, white snakeroot is of the greatest been shown to be the cause of the mysterious milk sickness or trembles that affects cattle expecially but may also affect horses and sheep and people drinking milk from poisoned cows. Cocklebur is also important in some sections as a
losses of livestock.
interest as it has
cause of livestock poisoning.
The cotyledonous
stage of the to readily eaten, poisonous cattle, but older seedling, are not relished are and harmless. A conapparently plants siderable number, especially ragweeds (Ambrosia spp.) and
which
is
is
goldenrods (Solidago spp.), are causes of hay fever.
FAMILIES OF DICOTYLEDONS
The
193
have given the family a prominent place That the great heads of dahlias, chrysanthemums, asters, and daises are thought of as flowers rather then inflorescences does not detract from their beauty. To these names may be added those of the rudbeckias, goldenrods, and a host of wild composites.
for
flower-like heads
decorative
In
purposes.
number of official drugs produced the Compositae are among much value as those of
the highest, although these are not of as the Solanaceae, for example.
species are important as weeds, the worst being Canada dandelion, cocklebur, sowthistle (Sonchus spp.), Chinese and blue lettuce (Lactuca spp.), and Iva spp.
Many
thistle,
CHAPTER
VIII
FAMILIES OF MONOCOTYLEDONS In number of families, genera, and species the monocotyledons numerous as the dicotyledons, but certain families, e.g., the Gramineae, are of outstanding importance. The origin of the monocotyledons has been the subOrigin. are not nearly so
much
For some years they were thought to controversy. than the be more primitive dicotyledons and probably ancestral This to them. belief, however, is out of harmony with both
ject of
morphological and paleontological evidence. It is now generally conceded that the dicotyledons are the older and gave rise to the monocotyledons. The prevailing belief today is that the monocotyledons were an offshoot of the primitive dicotyledons back in the early part of the Mesozoic era, and that they are monophyletic, i.e., of one origin, the first monocotyledons being A third and newer conception is that the ancestral to all others. not a simple monophyletic group but are are monocotyledons different members having sprung at different times poly phyle tic,
from distinctly separated representatives of the dicotyledons. The problem has been simplified by Coulter 1 and his associates, who have shown that cotyledons originate, not from a terminal ' cell but from a peripheral cotyledonary zone' that may develop one, two, or several cotyledons, or, in a few species, none at all. In both subclasses of angiosperms two generally start, but if growth continues in only one, the embryo is monocotyledonous. The fact that the two subclasses can, in most cases, be distinguished not only by their cotyledons but also by the venation of the leaves, the arrangements of bundles in the stem, floral and size of the endosperm is evidence of a monophyletic
structure,
group.
With regard to these other called to the fact that not all
characters, attention has been monocotyledons and dicotyledons
are typical of their groups in all respects. 1
COULTER,
J.
M.,
The
The
atypical struc-
Origin of Monocotyledony, Ann.
2: 175-183, 1915. 194
Mo.
Bot. Gard.,
FAMILIES OF MONOCOTYLEDONS
195
lures are not, however, characteristic of large groups of monocotyledons or dicotyledons but are quite scattered. Examples are the netted veined leaves of Smilax, Trillium, and Arisaema
and the somewhat scattered vascular bundles in the stem Thalictrum, Peperomia, Podophyllum, and Nymphaea. Description.
The monocotyledons
plants, but some tions the leaves
(e.g.,
palms) are large
are
of
mostly herbaceous
trees.
With
rare excep-
have unbranched parallel veins running either The embryo has one longitudinally or from the midrib outward. cotyledon that remains below ground with the endosperm during germination. A second may be present in more or less rudimentary condition. The stem is not divided into bark, wood, and pith, but the vascular bundles, collateral in type, are
The floral scattered throughout a soft pith-like parenchyma. parts are usually in threes or multiples of three, i.e., 3-merous.
The
calyx in %/
many 1,
species
is
colored and corolla-like.
ALISMACEAE.
Waterplantain Family
These are mostly aquatic plants with simple morphology that them among the lowest of the monocotyledons and close to
places
FIG. 78.
Alisma subcordatum (Alismaceae). (From Britton and Brown.)
A TEXTBOOK OF SYSTEMATIC BOTANY
196
the ancestral Ranales. There are only about 14 genera and 60 species, widely distributed in warm and temperate waters. Familiar Examples. The best known are the waterplantains (Alisma spp.) and the common arrowheads (Sagittaria spp.). Stems and Roots. The plants are perennial, herbaceous and succulent, growing in marshy places or shallow ponds. Leaves. The leaves are simple, mostly entire and sheathing the stem.
The
Inflorescences and Flowers. whorls.
often
flowers are solitary or in
are trimerous, with three or six stamens and The pistils are unicarpellate and few to insertion.
They
hypogynous
The petals are usually white and showy. and Seeds. In most species the fruits are achenes. Economic Significance. The plants have some value as ornaSome species of mentals, being grown in ponds and aquaria. edible tubers of limited value. have Sagittaria
many in each flower. Fruits
v
2.
LILIACEAE. 3
3
CA Co S
Lily
Family
6 < 3 >P
The lilies and their relatives constitute a large family of splendid ornamental plants. There are about 200 genera and 2,500 species distributed all over the world and very plentiful, both cultivated, throughout the North Temperate Zone. authorities would divide this family into three: Melan-
and
wild
Some
thaceae, Convallariaceae,
and
Liliaceae.
Familiar Examples. Examples are the true lily (Lilium spp.), but not the callalily (Zantedeschia aethiopica Spreng.), adders-
tongue or dogtooth violet (Erythronium spp.), hyacinth (Hyacinthus orientalisL.), tulip (Tulipa spp.), lilyofthevalley (Convallaria
wajalis L.), onion (Allium spp.), asparagus (Asparagus officinalis L.),
and Spanishbayonet (Yucca
spp.).
It
must be remembered
that some dicotyledons with large, showy flowers are called but do not belong in this family.
lilies
Stems and Roots. The Liliaceae are nearly all perennial or biennial herbs, but a few shrubby species of Dracaena and Yucca In most species the conspicuous are found in the subtropics. or a corm, rarely a rootstock. is a bulb underground portion grow from these fleshy portions. In some cases the bulbs or corms serve merely to store food for seed pro-
Many
fibrous roots
FAMILIES OF MONOCOTYLEDONS
197
duction the following year. In others they form in considerable for vegetative propagation. Leaves. The leaves of Liliaceae are all simple and parallelIn shape veined, but otherwise they are somewhat variable.
numbers and serve
they grade from linear to broadly ovate. In others they all basal.
are are
In some species they
.
alternate,
opposite,
or
whorled. Inflorescences and Flowers. Various forms of inflorescence
found racemes, panicles, umbels and not a few species have solitary flowers. are
and
The flowers likewise are variable, but as a rule they are trimerous
and bisexual and have
petal-like sepals, equal petals, six stamens,
and a
tricarpellate pistil with a
superior ovary, three seed chambers, and one style with a three-
In many species they are large and beautiful. Fruits and Seeds. The fruit is either a berry or a three-chambered capsule with loculicidal
lobed stigma.
dehiscence, i.e., directly into the seed cavities (except in Colochortus).
varies
The number
of seeds
from few to many.
contain a small
They
embryo within a
large endosperm.
Economic Significance.
From
the
esthetic
standpoint
Fio. 79. Lilium philadelphicum (Liliaceae). A, longitudinal section of flower. J5, floral diagram. (After
Bergen and Davis.)
few families of plants compare with the Liliaceae. The great abundance, variety, and size of the flowers give them much prominence in the greenhouse, flower garden, dooryard, and field. The fact that many of them can so easily be grown from bulbs or corms brings them into the humblest homes and the stateliest mansions. Their use for human food is limited to asparagus and Their forage value is low. They are not troublesome as onions.
198
A TEXTBOOK OF SYSTEMATIC BOTANY
Death camas. At least Fio. SQ.Zygadenua venenosus (Melanthaceae) and southward are four species of Zygadenus found from Montana westward inown to be poisonous from the presence of the alkaloid zygademne. (One-half natural size.) .
FAMILIES OF MONOCOTYLEDONS weeds, but the deathcamas (Zigadenus venenosus be mentioned as a poisonous weed. 3.
3
CA Co S
Wats.) should
Rush Family
JUNCACEAE. 3
S.
199
3- 6
P
The rush family consists of 8 genera and about 300 species of In herbaceous, aquatic, often grass-like or sedge-like plants. reality they are more nearly related to the lilies than to the grasses and sedges, and they are included in the order Liliales.
Familiar Examples. Familiar examples common or bog rush (Juncus effusus
are L.)
and woodrush (Luzula
parviflora (Ehr.)
Desv.) but not bulrushes, which belong to the Cyperaceae. Stems and Roots. The Juncaceae are all herbaceous and mostly perennial, growing in dense bunches often 1 to 3 feet The stems may be cylindrical or high. angled and contain a soft pith. The roots are fibrous.
Leaves.
The
leaves
are
linear
but
In the larger In sheaths are split. the genus, Juncus, the other, Juncoides, they are closed. variable as to thickness.
Inflorescences
and
Unlike
Flowers.
Fio. 81.
procarpus
Juncus lam(Juncaceae).
inflorescence. flower, c, gle a,
6,
sin-
pistil.
(After Strasburger.)
the grasses and sedges, the inflorescences are not made up of spikelets but of single flowers arranged in different
ways
racemes,
panicles,
corymbs, heads,
or
false
umbels.
The
flowers in most species resemble in structure a reduced There are three sepals and three petals of similar, broad, lily. greenish-brown scales. The stamens are typically six in number but in some species have been reduced to three, four, or five. The The pistil has three distinct carpels and usually three cavities.
general effect of the inflorescence
is
that of a sedge, olive-green or
brownish in color; but close inspection shows a flower structure
more
like the
lilies.
and Seeds. The fruit is a tiny capsule containing three seed chambers, or by the omission of partitions only one. SevFruits
A TEXTBOOK OF SYSTEMATIC BOTANY
200
eral seeds are
and straight Economic
produced in each chamber.
The embryo
is
small
in a fleshy endosperm.
Significance. Economically the Juncaceae are of importance. Most species are wholly ignored by livestock, but a few, notably the woodrush, which grows in nonswampy little
land, are relished. 4.
ARACEAE.
Arum Family
X The family Araceae
contains about 100 genera antf 1,500 They tend species, most of which are subtropical or tropical. to be aquatic but some are epiphytic.
Familiar Examples. The common calla or callalily of greenhouses (Zantedeschia aethiopica Spreng ), Jackinthepulpit or Indian turnip (Arisaema triphyllum (L.) Schott.), sweetflag (Acorus calamus L.), and skunkcabbage (Symplocarpus foetidus Nutt.) are familiar examples. Leaves. The leaves are mostly large, simple or compound, usually parallel -veined, but netted in some species, as Arisaema In the western skunkcabbage (Lysichiton kamttriphyllum. (L.)
schatcensis (L.) Schott.), they are of enormous size and half as wide. In Monstera dehciosa
feet long
more than 3 Liebm.
of the
tropics, sometimes grown in greenhouses, the huge leaf blades are perforated with many natural openings, 1 to 3 inches long by J/<2
to
1
inch wide.
The Araceae are herbaceous, or the larger forms slightly woody. Some are vine-like and climb by aerial roots. Epiphytic forms are occasionally found in the tropics. Underground stems are usually developed in the form of rootstocks, tubers, or corms, which often have a very pungent Stems and Roots.
taste.
Inflorescences
and Flowers.
The
striking
feature
of
the
Araceae is the inflorescence. This consists of a spadix subtended by a spathe. This entire structure is sometimes of astonishing appearance, being nearly 3 feet long in devilstongue (AmorphoIn callalily and most phallus rivieri Dur.) and colored deep red. other members of the family the inflorescence commonly passes for a flower.
The
true flowers are unisexual or rarely bisexual.
Generally the staminate flowers are at the top of the spadix and
FAMILIES OF MONOCOTYLEDONS
201
he pistillate below, but some species are dioecious. The perinth is reduced to tiny scales or ridges or is entirely lacking, ^here are commonly ten stamens or fewer. The single pistil has
ne to several carpels. Fruits and Seeds. The fruit is a berry or utricle. In some pecies the seeds contain endosperm; in others there is none.
Arisaema triphyllum and Arum (Araceae). A, entire plant. B, FIG. 82. D, staminate C, pistillate flower. padix with portion of spathe cut away E. inflorescence. S, staminate flowers. P, pistillate flowers. lower. (After Curtis.)
Economic Significance. General interest in this family is The corms centered in the beauty or oddity of the inflorescence. >r
tubers are edible in a few species, but they are generally too be palatable. A few of the members are reputed to be
icrid to
3oisonous.
The calamus
of the
ootstocks of Acorus Calamus.
drug trade
is
obtained from the
A TEXTBOOK OF SYSTEMATIC BOTANY
202
J
PALMACEAE. Palm
5.
Family
~ CA 3 Co 3 S 3 6 P
a family of tropical and semitropical trees and shrubs of species. They are naturally of wide their beauty they have been extended as far into the southern United States as the climate will permit.
This
is
some 140 genera and 1,200 distribution, and because of
The
smaller species are grown extensively in greenhouses. The ornamental species are found in sev-
Familiar Examples. eral genera,
and
also
we have
large interest in the
datepalm
(Phoenix dactylifcra L.), the coconutpalm (Cocos nucifcra L.),
and palmetto (Sabal palmetto Lood.). The palms are mostly trees, some of them there but are a considerable number of shrubs and great height,
raffia
(Raphia
ruffid),
Stems and Roots. of
a few woody vines. Leaves. The leaves are persistent, very large in size except on the vines, and either compound or, if simple, deeply cleft and On the larger trees they form a dense tuft at the top of plicate. the unbranched trunk, the basal ones dying as new ones are formed in a huge bud at the top. Inflorescences and Flowers. The prevailing inflorescence is
Some
a spadix.
of these are simple, others are in great panicu-
with a large spathe covering the cluster during development. The flowers are small and greenish, trimerous, the three carpels usually united and each containing one ovule in most late clusters
species.
Fruits
and Seeds.
The
fruit is usually
a drupe that develops
The carpels, the other two degenerating. is large, especially in the coconut, where it forms the
from one of the three
endosperm
bulk of the edible portion.
Economic
Significance.
Most
species in use are
grown
for
ornamental purposes, often giving a tropical appearance to the The value of coconuts and dates is well known, landscape. 6.
CYPERACEAE.
Sedge Family
The
sedges, often called sloughgrasses, resemble the true grasses so much that they are commonly mistaken for them. There are about 75 genera and 3,200 species, widely distributed
over
all
parts of the world, but especially abundant in wet
soils,
FAMILIES OF MONOCOTYLEDONS
203
Only about 10 per cent
of the species are found in the United are sedges distinguished from the grasses by the* some of which there are occasional excepfollowing characters, to States.
The
tions: (1) angular
stems without
joints, (2)
three-ranked leaves,
only one glume at the base of each flower, (5) perianth composed of bristles or lacking, and (6) seed free from wall of fruit (achene). (3) closed leaf sheaths,
(4)
Familiar Examples. Sloughgrass (Carex spp.), bulrushes (Scirpus spp.), and umbrella plant (Cyperus altcrnifolius L.) are the commonest examples. Stems and Roots. The Cyperaceae are practically all her-
The stems rarely biennials. are usually solid and without nodes between inflorescence and In the majority of species they are triangular, but in crown.
baceous, annuals or perennials,
some they are quadrangular, flattened, or cylindrical. The roots are fibrous and fascicled, many of them on perennial species being adventitious from underground rootstocks. Leaves. The leaves are mostly linear and grass-like, but the leaf sheath in nearly all species is closed. They have a three-
ranked arrangement on the stem.
much
Inflorescences and Flowers. is
The
li
gules are absent or very
in the
Gramineae, the spikelet
reduced.
As
the unit of structure in the inflorescence.
The
flower structure
reduction of the perianth to a few The flowers have a bristles, and even these may be absent. in the Gramineae. of as base instead two the at glume single differs chiefly in the further
There are typically three bisexual or unisexual. stamens but sometimes more or fewer. The carpels are united in the pistil, which has two or three styles or style branches. The fruit is an achene, usually threeFruits and Seeds. This is free from the ovary wall and one seed. angled, containing
They may be
has a very small embryo and a large soft endosperm. Economic Significance. Compared with the Gramineae the Cyperaceae are of limited importance. The grains as a rule are small, few in
number, and
insignificant.
However,
many
species
regions and make good pasturage. Others are too succulent in the spring and too hard and wiry in
grow extensively
in
swampy
the fall. This harsh texture is due in part to serrations on the leaves and in part to deposits of silicates in the leaves and stems. The papyrus, early used for papermaking, belongs to this
A TEXTBOOK OF SYSTEMATIC BOTANY
204
SC
FIG. 83. pistillate
Carex rostrata (Cyperaceae)
.
A, apex of flowering stem with one
and two staminate spikes (Xl).
igynium (X8). D, achene, continuous with stigmas (X8) E, floral diagram.
C, perB, pistillate scale (X8) persistent, twisted style and three
FAMILIES OF MONOCOTYLEDONS family, but
it
has been largely superseded by straw, linen, and
wood pulp. None of the Cyperaceae
is
tant as weeds except where
swampy
J
7.
205
poisonous, and they are unimporland is cultivated.
GRAMINEAE (POACEAE).
The Gramineae
Grass Family
constitute the second largest family of
mono-
Of cotyledons, containing about 400 genera and 4,500 species. the species found in the United States more than three-fourths
The grasses are the most universally distributed, and are native. the most numerous in individuals, of any family of spermatoThe great adaptability of the different species has phytes. enabled them to thrive under the most varied conditions: in standing water and in deserts, on sun-baked hillsides and in all but the most densely shaded forests, in sand and in gumbo clay, far above the timber line on lofty mountains, and well into the arctic regions. Fossil remains of grasses have been found in rocks of the Lower Cretaceous period, but in all probability the great diversity of
form now found within the family is a relatively recent development. Their simplicity is due to degeneration or specialization It is probable that the order rather than to primitiveness. Graminales should be looked upon as a specialized side branch of the main genetic line of monocotyledons, and as one that has given rise to no other orders. Familiar Examples. The well-known members of the Gramineae are too numerous to mention. Representative examples are wheat (Triticum aestivum L.), corn (Zea Mays L.), oats (Avena saliva L.), rice (Oryza saliva L.),
sorghum (Holchus Sorghum L.), L.), bamboo (Bambusa spp.), and Kentucky bluegrass (Poa
sugarcane (Saccharum officinarum
timothy (Phleum pralense
L.),
pralensis L.).
Stems and Roots.
The
grasses are nearly all herbaceous.
a cylindrical culm with conspicuous nodes and hollow internodes, although solid stems are not unusual among the larger members such as corn, sorghum, and Annual, biennial, and perennial species are all sugarcane. numerous. The largest woody species are the bamboos, which may grow to more than 100 feet in height and several inches in
The
prevailing type of
stem
is
206
A TEXTBOOK OF SYSTEMATIC BOTANY
diameter.
Among
the
perennial
grasses
there
is
a marked
tendency to the formation of rhizomes, underground rootstocks that in some species, such as quackgrass, extend for a considerable distance and serve the function of vegetative propagation. The Small tubers or corms roots are usually fibrous and fascicled. are found in a few species. Leaves. Almost without exception the blade (lamina) of the leaf is narrow and ribbon-shaped. The arrangement on the stem is alternate
and two-ranked.
The
leaf
is
attached to the node by a long sheath, which clasps the stem. This sheath in
most species
is split
throughout
its
length on the side opposite the attachment of the blade. The union of blade
and sheath
is usually not a smooth Often it appears as if the blade attached slightly below the top of the
one.
[floret
sheath, and this apparent projection of the sheath above the attachment It is thinner and called a ligule. more membranous than the sheath proper and is sometimes fringed. The base of the blade at its two margins often projects to form two small ear-
is
ume .first glume. .pedicel
like portions called auricles. Spikelet of Bromus marginatua showing the glumes and several florets typical of the Gramineae. (One-half natural size ) FIG. 84.
Inflorescences and Flowers. inflorescences
grasses
are
and
The
of
the
highly specialized,
and
flowers
until their structure has been mastered,
they seem difficult to understand. The inflorescences are composed of several to many spikelets, which are combined in various ways on a main axis called the rachis. Some are in spikes, as wheat, others are in racemes, as certain of Festuca and Paspalum, while still others are in panicles, species as oats. It should be understood, however, that the panicles of
compound
Pamcum, etc., are not quite comparable with the panicles of Yucca, Heuchera, and Thalictrum, for example, since in the former each slender stalk bears a spikelet of flowers while in the latter it bears a single flower. Avena,
FAMILIES OF MONOCOTYLEDONS
207
Each spikelet bears one to several florets attached to a central stalk or rachilla. The usual structure of a spikelet is as follows: At the base is a pair of glumes, the lower, outer one called the and the upper, inner one called the second. Above the Each glumes, and partly enclosed by them, is a series of florets.
first,
SECOND GLUME
FIG. 85.-
floret
Representative spikelet of grass. The rachilla here show the parts more clearly.
has at
its
base a lemma and a palea.
is
elongated to
The lemma
is
the
lower, outer scale of the floret, which in many species bears a long slender awn or beard as an extension of the midrib at the tip or In its axil the floral parts are borne. The palea, often back.
with two longitudinal ridges them and the rachilla. The
(keels or nerves),
stands between
floral parts consist of a perianth
A TEXTBOOK OF SYSTEMATIC BOTANY
208
(sometimes absent) that is reduced to two or three minute scalestamens (one, two, or six in a few species), and a central pistil of three united carpels, only one of which is func-
like lodicules, three
tional. The superior ovary bears two (rarely three) feathery stigmas with short styles or none. Many species have other florets on the rachilla, the upper or lower of some being sterile.
ovary lodiculc
Floret Representative floret of grass,
FIG. 86.
parts,
and
species.
much
this has
The
unknown, but
is
taken place in varying degrees in different
perianth it is
enlarged.
complicated by the fact that suppression and modification of floral
Flower study in the grasses there has been
much
condition
not unlikely that
the grass ancestor is consisted of two whorls of
of it
Three lodicules can still be found in some There probably were six stamens, this number still species. being found in bamboo and in rice. The pistil doubtless had three parts each.
three carpels; in fact, studies in the early development of the flowers have shown that this number still persists, although they
FAMILIES OF MONOCOTYLEDONS
209
are so intimately fused that they appear as one. Three styles, In most species suggestive of as many carpels, are not unusual.
the flowers are bisexual, but in corn, for example, the stamens and Even here bisexual flowers in the pistils are in separate flowers.
staminate tassels are fairly common. This specialized floral structure furnishes ground for the belief that the grasses are not primitive plants but derivatives of lily-like ancestors. Fruits and Seeds. The one-ovulate pistil develops into a hard, dry, seed-like fruit, similar to an achene, but strictly speaking a caryopsis, since the seed adheres closely to the surrounding ovary
In some species, such as oats and hulled barley, the palea wall. and lemma continue to enclose the grain after threshing. The
FIG. 87. pi,
pistil.
pa, palea.
Floral diagram of grass. 8, le,
stamen,
lo,
lemma,
r,
lodicule. rachilla.
Poition of leaf of Elymus Fiu. 88. at the level where the culm emerges
from the sheath.
(Three times natu-
ral size.)
is composed largely of starchy endosperm with a relatively small straight embryo near the point of attachment. Economic Significance. Undoubtedly the Gramineae excel
seed
other families in their importance to mankind. Without Pinaceae we might live in earthen houses; without cotton we might clothe ourselves in other fabrics; but without Gramineae all
most of us would starve. Notwithstanding the prevalence of hundreds of other families of plants the earth would support far less animal life were it not for the grasses and grains. The explanation is not difficult. In the first place, the grasses are abundant; they grow everywhere, under all conditions, filling in the spaces between larger plants and crowding out those that In the second place, they withstand are poorer competitors. injury unusually well, rallying promptly when cut or eaten off. How many other species can withstand steady pasturing by live-
A TEXTBOOK OF SYSTEMATIC BOTANY
210
stock or the daily use of the lawn
mower?
Then, too, they are
palatable and nutritious, and practically none are poisonous. The Gramineae furnish summer forage, winter hay, grain for
and bread for man. Of the different grains, wheat and rice are outstandingly the most important, considering the entire human race, with corn, oats, barley, and rye trailing after. From the food standpoint we must not overlook sugarcane, which furnishes nearly two-thirds of the world's sugar. Aside from the food supply the Gramineae have some imporWe in America can hardly appreciate the extent to which tance. bamboo is used in certain parts of the world where timber is Its great size, strength, and lightness adapt it well for scarce. bridges, buildings, furniture, and implements, while much of the
livestock,
waste
is
used for
Not even
fuel.
the stately pines or the showy flowers contribute more to the adornment of the earth
than do the beautiful carpets of grass that hide her nakedness.
Only a few members of the Gramineae known to be poisonous, and most of these only under certain conditions. The cyanophilic group, Holchus and the closely related Sorghum, are the most arc
important of these. Cultivated sorghum, which is a valuable forage plant under normal growing conditions, has f Cattle from CaUSed SCri US loSSeS hydrocyanic acid poisoning during a A few other species including
drought or following a frost.
sleepygrass, Stipa robusta, and stinkgrass, Eragrostis tilianensis, Others protect themselves by sharp saware listed as poisonous.
teeth on the margins of the leaves and
As would be expected among plants
by
spines.
so adapted to competition
with other forms of life, many pernicious weeds may be found. Notable among these are cheat or chess (Bromus secalinus L.),
downy brome
grass or military grass (B. tectorum L.), quackgrass or couchgrass (Agropyron repens (L.) Beauv.), wildoat (Avena fatua L.), green bristlegrass (Setaria viridis (L.) Beauv.), and foxtail
barley (Hordeum jubatum L.).
FAMILIES OF MONOCOTYLEDONS
211
COMPARISON OF THREE FAMILIES OF GRASS-LIKE PLANTS Untrained persons make no distinction between the three comfamilies of grass-like plants. The following table compares It must be remembered, however, that these three families. most generalizations are not without exception.
mon
8.
IRIDACEAE. Iris Family CA 3 Co 3 S 3
P
About 60 genera and 1,000 species widely distributed in temperate and warmer regions, becoming fewer northward, constitute That they are among the highest members of the this family. Liliales is shown by their inferior ovaries and reduced stamen number and by the united filaments in Sisyrinchium. Familiar Examples. The best known examples are the different kinds of iris, flag, or fleur-de-lis (Iris spp.), both wild and cultivated, gladioli (Gladiolus spp,), and the blue-eyedgrasses (Sisyrinchium spp.).
J3U1 'AM Y
Stems and Roots. most of them have
The
all perennial herbs, and underground rootstocks, corms, or
Iridaceae are
fleshy
bulbs.
Leaves. The leaves are mostly lanceolate or linear, tworanked, with clasping bases. Inflorescences and Flowers. The flowers are mostly large and showy, single or few in a cluster, and subtended by bracts.
The perianth is composed and three petals, forming a tube adherent to the ovary. The three stamens are attached to this tube opposite the sepals. The pistil is tricarpellate, with an inferior ovary divided into three chambers. The styles have three branches which are sometimes expanded and petal-like, as in Iris, where they add much to the appearance of the flower. Fruits and Seeds. The seeds are numerous in a dehiscent The endosperm is abundant and the embryo is small capsule. and straight. Economic Significance. Some of the finest of our flowers
They are bisexual and usually regular. of three petal-like sepals
belong to the Iridaceae. They are also interesting in showing the progress of evolution in the monocotyledons, culminating in the Orchidaceae. 9.
ORCHIDACEAE.
Orchid Family
CA 3 Coz 3 S 1
-2
P
The monocotyledons reach This
the climax of their development in
the largest family of the monocotyledons and the second largest of all the angiosperms, being exceeded
the Orchidaceae.
only by the Compositae.
is
Indeed,
it is
not unlikely that when the
tropics have been thoroughly explored the number of orchid There species will be placed first among the flowering plants. are at least 500 genera and 15,000 species, mostly tropical or subIn floral tropical but a few growing as far north as Canada.
complexity they surpass everything else in the plant kingdom, the It is specialization being largely to facilitate insect pollination. indeed debatable whether or not we are justified in calling the Compositae, the highest of the dicotyledons, more advanced than the
Orchidaceae,
the
highest
of
the
monocotyledons.
The
Compositae show the greatest advancement in inflorescence, but the Orchidaceae show the greatest advancement in floral
strut*-
FAMILIKH OF MONOCOTYLEDON X
213
tare, although, as has been pointed out by Bessey, much of the specialization in the Orchidaceae is in the petals, which are the
most
easily modified of all the floral organs.
Familiar Examples. Many well-known flowers belong to this family greenhouse orchids (Cattleya spp.), ladyslipper (Cypri-
pedium
FIG. 90.
spp.),
and coralroot (Corallorrhiza
Cypripedium hirsutum (Orchidaceae). corolla.
spp.).
Showing the highly
specialized
(After Sinnott.)
Stems and Roots. The Orchidaceae are perennial herbs, mostly terrestrial and green, but a considerable number epiphytic with aerial roots, and a few chlorophyll-less and either saprophytic or parasitic on the roots of other plants. usually erect but sometimes trailing or climbing. produce fleshy roots, rootstocks, corms, or bulbs.
The stems are Most species
Leaves. In most terrestrial and epiphytic species the leaves are fairly uniform except as to width, in which respect they vary from linear to broadly ovate. In saprophytic and parasitic species (Cephalanthera scales.
and
Characteristically
Corallorrhiza) they are reduced to
the
leaf
bases ensheath the stem.
In arrangement they are usually alternate, but sometimes opposite and occasionally whorled.
A TEXTBOOK OF SYSTEMATIC
214
Inflorescences and Flowers.
In
many
BOTANY
species the flowers are
but more often they are in racemes or spikes. The flowers are the most remarkable feature of the Orchidaceae.
solitary,
They present
so great a variety of detail that only the general They are bisexual and irregular, i.e.,
plan can be given here.
There are three sepals, either green bilaterally symmetrical. or colored to match the corolla, and like each other in appearance.
(lower Mae)
-functional anther
-Stommodia
/F'
v?lt
stigma
(lower side)
column
^^^^^ovary
'
CVPRIPLDIUM
CATTLLYA The two common
Fia. 91.
by
Two
types found In the Orchidaceae, represented (Drawings contributed by Florence Mekeel, of
floral
and Cypripedium. Hortorium, Cornell University.)
Cattleya
the Bailey
lobellum
and left mates and are below the .other two, is unlike the
of the three petals are alike or right
called wings.
The
third,
wings, often very much so, being bulbous, spurred, tubular, strap-shaped, or variously branched, and contributing most to the
beauty and oddity is
called the
lip.
This highly specialized petal characteristic part of the flower is that is made by a fusion of the three
of the flower.
The most
the gynandrium or column stamens with the pistil. Only one or two of the stamens are
and these usually produce two or more stalked pollen masses, pollinia, which are often waxy or even viscid. One lobe of the stigma oftens extends to form a beak the rostellum. The other two on either side are viscid and functional. These parts of the gynandrium are variously proportioned in functional,
FAMILIES OF MONOCOTYLEDONS different species,
and with the variable
The
combinations.
pistil is tricarpellate,
lip
215
give endless floral
with an inferior ovary
containing one cavity with many ovules. Fruits and Seeds. The fruit is quite regularly a three-valved capsule containing many seeds, which are very tiny, with an undifferentiated embryo and no endosperm.
Economic Significance.
The
flowers of the Orchidaceae are
the most cherished of any in the plant kingdom. Their culture in the greenhouse has become a fine art. In the tropics
remarkable colors, form, and profusion are a constant Even in temperate zones the ladydelight to the traveler. slippers and a few others make an important contribution to
their
the flora.
Unfortunately, the Orchidaceae are sensitive to abuse, and picking the flowers soon exterminates the plants. There are too many people so constituted that their impulsiveness far exceeds their
judgment.
They cannot seem
to learn the relative value
growing and those that are picked and wilting. In many sections where ladyslippers were once abundant, they can no longer be found or have become so rare that they are hunted the harder. of flowers that are
COMPARISON OF ORCHIDACEAE AND COMPOSITAE Since the Orchidaceae and Compositae are generally considered the highest types of the monocotyledons and the dicotyledons, respectively, some useful lessons may be learned
by a comparison
of
the two families shown in the table on
page 216.
From
be seen that even the most highly primitive with regard to certain structures. Indeed, more than half of the primitive characters ' of the angiosperms are illustrated in one or both of these highthis table
developed plants
est
'
it may may be
families.
The
relative
number
of stars in the
two columns does not
fur-
nish a safe criterion of the relative advancement of the two families, for the characters are not necessarily of equal imporThe student will, however, find it profitable to make tance.
similar comparative tables of other families, especially as relationships between families may often be brought out by such
comparisons.
A TEXTBOOK OF SYSTEMATIC BOTANY
216
*
A
star
the other.
here used to indicate that the condition is more advanced in this family than in In some cases there may be a difference of opinion as to which is the more
is
advanced, especially where regreBsive development has taken place.
*
CHAPTER IX NOMENCLATURE In a general
way
names
' the term ' nomenclature
is
used to cover an>
indeed, the names in use whether or not the> follow a system. Using the same names, plants might be classified in various ways or they might not be classified at all.
system
of
or,
of Nomenclature to Taxonomy. Conceivably s nomenclature might exist that would be independent ol classification. Such a nomenclature would supply a name tc each individual. In botany this would be quite impossible
Relation
system
of
As soon, however, as we assert that certain individuals are essentially alike and offer a specific name to the group, we arc linking nomenclature with taxonomy; for such a grouping is ii itself
a
carries us
The binomial systerr recognition of relationship. still further into taxonomy, for in it the name not onl>
designates a group of like individuals, the species, but it indicate* a larger group, the genus, where related species may be found
In systematic botany, then, nomenclature and taxonomy an inseparable
Names Usually Descriptive. It is natural that the name giver to a plant shall, in a measure, describe it or suggest something 01 someone connected with it. The name may refer to its appear ance, as buttercup; to its habitat, as watercress; to its properties as chokecherry or to some person that has been associated with it ;
Such terms have a meaning only to peopl< as Johnsongrass. familiar with that language, and, indeed, in the evolution of language the meanings of terms are often forgotten. Dandelion
J
rose, mullein,
yarrow, and huckleberry are doubtfully descriptiv<
today.
COMMON NAMES Probably all nations and tribes have given names to plants each in its own language. Such terms are learned in childhoo< and handed down from generation to generation. They an fairly definite if the plants have no closely similar relatives, a 217
A TEXTBOOK OF SYSTEMATIC BOTANY
218
cowparsnip, white sweetclover, basswood, and sassafras, but are loosely applied among plants having many similar kinds in a group, such as the grasses, willows, huckleberries, and goldenrods.
A common name may
or
not represent a species in the
may
Sometimes it includes everything within a genus, and it may be the generic name, as 7m, with or without a qualifying adjective, as Persian iris. In any event the same name is applied to all plants supposed to be of the same kind. botanical sense.
No attempt
is
made
to
name each
individual plant except in case
of unusual specimens mostly trees of sentimental value, The Value of Common Names. There is a tendency for systematists, especially beginners, to hold common names in con-
tempt.
This attitude
The common name
is
natural enough but
may
be overdone.
generally somewhat descriptive to those using it and is easily learned and remembered because of its familiar sound, even though long, as Jackinthepulpit, dogtooth violet, and bachelorsbutton. In the majority of cases, is
the approximate accuracy of the name is sufficient for the purposes of the person using it, as pine or elm. If a little more definiteness is desired, an adjective may be added, as yellow pine or slippery elm.
name
It is safe to say that, as a rule, the
common
quite satisfactory to the nontechnical person and more satisfactory than the so-called scientific or botanical name would be.
is
The common name may be monomial,
binomial, trinomial,
or polynomial.
There aie three prinof Common Names. in names: common defects (1) They may be quite indefinite. cipal the are restricted to people of one language or even one (2) They
The Weaknesses
section of a country. stituted authority.
We now
(3)
They
hold that unless a
mous with the
are not regulated
common name
specific name, or in
is
some cases a
by any con-
strictly
varietal
synonyname, it
too vague for scientific usage. Buttercup, daisy, and goldenrod In a large country a plant may be called are familiar examples. as different names, pennycress, fanweed, and stinkweed. On by the other hand, the same name, as bluebell or bunchgrass, may be
is
applied to several different plants.
Such
differences in usage are
and make highly confusing, provoke many scientific for the terms wholly unusable purposes. To a traveler in a foreign country, the local names encounfruitless controversies,
NOMENCLA TUBE
21 9
more troublesome than botanical names, for they and have the disadvantages found in all common names, and if one travels or reads extensively he has many sets of names to learn. There is no court of last appeal to settle controversies concerning the accuracy of common names. We have, to be sure, a book ' Standardized Plant Names' entitled (see page 323), which is a move in the right direction and valuable as far as it goes, but it is Most of the lists of common names of wild far from complete. plants make a free use of synonyms, and if any person or community wishes to adopt a new name for a plant, as has been done hundreds of times, there is no authority to stop it, and the confusion is tered are even
are just as hard to learn
increased.
BOTANICAL OR SCIENTIFIC NAMES Every science has developed a terminology
of its
own, a set of
technical terms peculiar to the subject matter of that science. In systematic botany these technical names of plants number
thousands and are far in excess of the common names. Origin and Nature of Botanical Names. To get a correct conception of scientific names the reader must understand something of their composition. Many of the older names are Greek in origin but are now used in Latinized form, and the later ones are mostly Latin. The earliest Greek and Latin names were, in At the reality, the common names used in those countries. present time each kind of plant is given a generic name followed
many
The generic name is a noun, and the specific epithet takes the form of a modifying adjective indicating which of the several members of the genus is being by a
specific
name
or epithet. 1
considered.
Generic Names. The generic name indicates in a general way the kind of plant under consideration. Thus, Quercus is the name of all kindj of oaks, Acer is the name of all kinds of maples, and Lupinus is the name of all kinds of lupines. Some genera are 1 The most recent code of botanical nomenclature makes a distinction between the name of a species, which is the binomial by which it is designated, and a specific epithet, which is the last word of the binomial; e.g Agrostis alba L is the specific name of a certain grass, but alba is the specific If this distinction comes into general use, confusion epithet of that grass. will be avoided. ,
A TEXTBOOK OF SYSTEMATIC BOTANY
220
such bold, clear-cut, natural groups that they are easily recognized even by the layman. Examples are pines (Pinus), grapes Others are distinguished from their (Vitis), and roses (Rosa).
by more obscure characters and are not easily recognized by untrained persons, who may include plants from different genera under one name, such as goldenrod, bunchgrass, and wild On the other hand, they may give different names to differpea. ent sections of the same genus, e.g., plum, cherry, etc., for Prunus, and pumpkin and squash for Cucurbita. The trained botanist relatives
recognizing genera than species used in a technical sense the generic name should always begin with a capital letter, but some are also used as common names, such as crocus, ins, spirca, and rhododendron, and when so used they begin with small letters. Usually the generic name suggests or describes some character of the plant, as illustrated by Tnfolium (three-leaved) and A few generic names are given in honor Corallorhiza (coralroot). of people, e.g., Linnaea and Cogswellia. The specific epithet is a qualifySpecific Names or Epithets. ing term making it possible to distinguish each member of the genus from the others. Most commonly it is a descriptive It may, adjective, such as alba (white) or vulgaris (common). from a be taken the of name person however, (e.g., Besseyi or from the name of another or Brittoni) genus; e.g., Exoascus Pruni is the species of a parasitic fungus that attacks trees of the genus
has
less difficulty
When
Prunus. In botanical nomenclature specific epithets are written with small initial letters with the exception of those that are derived from names of persons or are taken from generic names. In bacteriology and in entomology small letters are used exclusively. Although there is some defense for the claim that the genus rather than the species should be considered the unit of nomenclature, it is
more common
in
modern taxonomy
to treat the
species as the unit. Origin of the Binomial System.
The present binomial system nomenclature had a long evolutionary development. Cato, in his 'De Re Rustica' written about two centuries before Christ, used two names for plants, although he lacked the modern conof
ception of genera encies
came
in.
made up One was
Later, two tendto translate the descriptive Greek
of several species.
NOMENCLA TURE
22
1
nouns used for genera into Latin, in which language they took the form of two words, i.e., binary generic names. The other was to Both these methgive a descriptive phrase for the specific name. ods resulted in what have been called polynomials. Brunfels, in the middle of the sixteenth century, changed many binary generic names to single ones, and Dodonaeus, a few years later, followed for the most part binomial usage similar in principle to that of today. Gaspard Bauhin in his 'Pinax,' a list of some 6,000 plants, written in 1623, used the binomial system even more extensively,
None
though not exclusively.
however, impressed upon the botanical world of his time the desirability of abandoning all practice other than binomial, and works continued to appear having mixed usage
of these writers,
monomial, binomial, trinomial, and polynomial. They Linnaeus to more fruitful efforts through
did, probably, influence
philosophical discussions of the subject in his 'Philosophia Botanica' (1751), and to a general practice of one generic name, specific epithet in his 'Species Plantarum' (1753), which, however, was sometimes followed by a varietal name. Advantages of Botanical Names. Two great advantages are commonly claimed for botanical or 'scientific' names: (1) that
and one
they are the same among scientific people the world over and We shall see presently (2) that they are uniformly binomial. that, while these
two
qualities are usually found, there are
some
exceptions. greatest advantage of the botanical name is its exactness. our present system of nomenclature were perfected, each kind of plant would be called by one binomial name only (aside from its common names), and that name would mean the same species Even now this situation exists with regard to to all botanists.
The
If
the great majority of plants that have been discovered and named, but in unexplored regions, especially in the tropics, there
many species that have not yet received botanical names, and among those that have been studied the names of a few are still in are
While binomials are the rule, a few plants bear controversy. varietal or other subspecific names (see page 256), resulting in trinomials.
claimed that the botanical name has the special advantage of being descriptive of the plant. This claim has little force, however, for most common names are likewise It is also
A TEXTBOOK OF SYSTEMATIC BOTANY
222
and since the majority of botanists today, especially the younger ones, are not skilled in Greek and Latin, they do not appreciate the descriptive value of most of these terms. descriptive,
A further advantage of the botanical name is that it is governed some measure by
in
many names made
and have been rejected.
international rules of nomenclature,
in violation of these rules
Disadvantages of Botanical Names. The usual objection names is that they are so long and hard to
offered to botanical
In reality the difficulty lies not so much in their length as in their unfamiliar sounds and combinations. Oxyria digyna and learn.
Ruellia strepens are not long names, but most people would think them hard because they are, to them, unfamiliar and meaningless.
Another reason why botanical names
will often
be unusable to
the fact that they require an exact delineation of species; and while some species are clearly defined, with easily recognized characters, others look so much alike that technical
the layman
skill is
lies in
required to separate them.
NONVALID NAMES
Many of the names that have been applied to groups of plants have been found unusable for various reasons. Some of these names have been given by excellent botanists who have unavoidably fallen into error; others have been due to the carelessness or crudeness of poorly trained men whose zeal to propose new names has exceeded their ability to apply them. By
Synonyms.
the rules of botanical nomenclature, given group can have but one valid
later in this chapter, a plant or
name, and no two groups can have the same name. For various reasons, however, many species have received two or In such cases methods have been devised for more names. determining the one valid name, and all the others are classed as synonyms, or, according to certain usages, the term 'synonym' is applied to both the valid name and the nonvalid ones. While scientific
1
synonyms also be
are
commonest
in the designation of species,
they
may
found among generic and family names.
According to N. L Britton, 'Illustrated Flora,' 1st ed., 1896, Vol. I, Introduction, p. viii, some species have been given from ten to twenty names, and 'for about 200,000 known species of plants there are not fewer than ' 700,000 recorded names or an average of more than three names per species. 1
NOMENCLATURE
223
'A name
is rejected when there is an older valid the same type 1 (typonym).' 2 Typonyms are sometimes called absolute synonyms because the older valid name
Typonyms,
name based on
and the new nonvalid ones
refer unquestionably to the
same plant
or group.
A
few examples will serve to make clear the nature of typonyms. In 1894, G. S. Jenman gave the name Asplenium Guild-
and 3 years later Hermann Christ named the same specimen A. Vincentis, thereby establishing a typonym.
ingii to a plant,
The generic name Miegia given by C. H. Persoon typonym of Arundinaria given by Andr Michaux
in 1805 is a
to the
same
species in 1803.
name
'A name
rejected when there is an older valid based on another member of the same group (metonym).'
Metonyms.
is
Had
the two species mentioned in the preceding paragraph been named from different type specimens, A. Vincentis might have
been called a metonym. Likewise, Miegia might have been regarded as a metonym of Arundinaria if it had been based on a
The generic names Bromus, Zernia, Serrafaland Forasaccus were based on different species. Most authorities consider all these to be the same genus; therefore, Bromus, the oldest, is the valid name and the four others are metonyms. Panicum pilosum Swarts, P. distichum Lam., P. pilisparsum Meyer, and P. trichophorum Schrad. were named from P. different specimens, which probably were of the same species. different species.
cus,
pilosum, being of the earliest date, should be regarded as the valid name and the rest as metonyms. It will be noted that personal opinion may enter into the determination of metonyms, for one taxonomist may regard the plants to which these names have been given as all one species,
notwithstanding very slight differences in them, while another may think these differences are great enough to justify different Such cases are rare, however, specific epithets. Metonyms and typonyms have arisen in several ways. In early days the seriousness of duplicate names was not appreciated.
The term 'type' as here used applies to the individual plant or plant group that was used as a basis for the description of the species or higher 1
category (sec p. 231). 2 This quotation and those defining metonym, homonym, and hyponym are taken from the American Code of nomenclature (see pp. 230 and 312). Although this code is no longer used, the terms are very convenient.
A TEXTBOOK OF SYSTEMATIC BOTANY
224
Botanical names up to the sixteenth century had somewhat the same stability that common names have today. If a botanist happened to know the name by which a plant was designated, he If not, or if he did not like the name in generally used that name. use,
he proposed another.
Furthermore, the
name
given a plant
was not always published with a description of the plant, as is the custom now. Since the time of Linnaeus a serious effort has been made to follow the names in use rather than to apply new ones. This is often difficult to do. Many names and descriptions have been published in obscure books, journals, and pamphlets, in various languages. Occasionally, also, two names have been published so nearly simultaneously that the first was not distributed to the botanical world until the second had been entered for publication. Furthermore, some botanists have not been careful to look up established names before proposing new ones. Sometimes the author of the earlier name gave the plant an imperfect description, and a later worker, seeing the same species in a different environment, believed he had found a different speIn the lower plants, especially the cies and gave it a new name. fungi, different stages in a life history have given rise to different Thus, Fusicladium dendriticMm, representing the conidstage of the apple-scab fungus, is a synonym of Venturia inaeThe uniting of qualis, the ascospore stage of the same fungus. two differently named groups erroneously supposed to be distinct names.
ial
will
always result in synonyms.
Homonyms. 'A name is rejected when preoccupied (homonym) .' The same name cannot properly be applied to two If this is done, the name is a homonym for different groups. every group to which it is applied except the first. In the binomial system the full name of a plant is the genus (noun) with the Therefore, it is permissible to use species (qualifying adjective). the same specific name in different genera, as Quercus alba, Melilotus alba,
and Chenopodium album.
use the same generic flexilis,
Likewise
it is
permissible to
name with
Pinus ponderosa, and
permissible to use the
different specific names, as Pinus Pinus sylvestris. It is not, however,
same generic and
specific
combination for
Asarum macranthum, Phaca villosa, among the numerous names that have
plants of different species.
and
Vitis virginiana are
been thus misapplied. generic,
family,
Neither
or ordinal
is it
names
same For groups.
permissible to use the for
different
NOMENCLATURE
225
name
Setaria has been applied to lichens In such a case the name is valid for (1803) and to grasses (1812). it was applied but a nonvalid homonym the first group to which
example, the generic
in its later application.
Most homonyms have arisen in this way: A botanist studying a species or other group that he believed to be new applied to it a name that was descriptive but had already been used, unknown to him. Since names are not completely descriptive of plants but rather suggestive of a conspicuous character, it is not surprising that the same name should fit two unrelated groups. Indeed, the same name has been appropriately applied to both a group of plants and a group of animals, as Cereus for a cactus and a sea
anemone and Hystrix
for a hedgehog and a grass. should be understood that a slight difference in the spelling Such a of a word does not necessarily make it a different word. difference may be due to a typographical error, to a contraction, It
or to the grammatical necessity of making the specific name in Latin correspond to the generic name. For example, Astrocarpus is
a contraction of Asterocarpus, and albus, alba, and album are, and neuter forms of the same
respectively, masculine, feminine, adjective meaning white.
'A name is rejected when the natural group to When a name is applies is undetermined (hyponym).' first applied to a group, the group should be so described, or illustrated, or referred to preserved plants, that its identity can be Hyponyms.
which
it
recognized
by other
botanists.
A name
not so described or
hyponym and nonvalid for the group for which it was intended. Names used with no descriptions are designated as nomina nuda; those with unsatisfactory descriptions, as nomina subnuda or ambigua. It is sometimes a matter of opinion whether
identified is a
The description, sufficiently defined. of identification other means or may be rather poor illustration, so that one botanist will think it usable and another will reject or not a
The
it.
name has been
generic
name
Aragallus, though classed as a
hyponym
Adodendrum Necker and hyponyms, and Gentiana hybrida Raf and Lechea furfuracea Raf are specific hyponyms. A distinction should Validity versus Legitimacy of Names. in be made between terms that are common use for branding names as correct or incorrect. Validity refers to whether or not a by some
is
used by others.
authorities, Calesian Adams are generic .
.
A TEXTBOOK OF SYSTEMATIC BOTANY
226
name conforms to all the rules of nomenclature. in harmony with all the rules is valid and is the
A name that is correct
name
for
conform to any one or more rules, it is invalid or nonvalid. Typonyms, metonyms, homonyms, and hyponyms are all nonvalid. Legitimacy refers only to whether or not a name has been accompanied by a suitable published description, If so, it is legitimate whether or or referred to a type specimen. not it conforms to the other rules. If not, it is illegitimate. The term applies to hyponyms (nomina nuda, nomina subnuda, and nomina ambigua). It follows that all valid names are legitimate, but not all legitimate names are valid. When deeper investigation Dividing and Uniting Groups. shows the desirability of dividing a species or other group, the original name is retained by the branch that contains the oldest named member, and a new name is proposed for the other branch. For example, the generic name Prunus was at one time used for both plums and cherries. Some have thought it desirable to divide the genus, and since Prunus domcstica, a plum, was the original species on which the genus Prunus was based, the plums retained the name Prunus and those cherries that were placed in a new genus were given the name Padus. When two or more genera or other groups are found to be identical in composition and to differ only in name, they are united under the oldest valid name, and the others become metonyms, as in the case of Bromus on page 223. use.
If it fails to
From the foregoing discussion of nonvalid names it will be seen that typonyms and metonyms represent two different kinds of synonym, and, furthermore, that homonyms and hyponyms result in the formation of synonyms, for these names must be replaced
by usable terms, leaving them
as synonyms.
CITING AUTHORITY FOR
With
so
many nonvalid names in botanical
difficult to
lessened
NAMES
The
determine valid ones.
by giving the name
immediately
literature
confusion
is
it is
often
somewhat
author (usually abbreviated) This designation of the author
of the
after the binomial.
in fact, considered a part of the full name of the plant and follows the specific epithet with no intervening punctuation mark, In a few as Lilium canadense L. and Mertensia virginica (L.) DC. is,
cases the binomial
is
followed
by a
varietal
name, and
in such
NOMENCLATURE
227
by the name of the author DC. The correct generic and specific name and authority are usually derived from the array of synonyms as follows: By an examination of the plant it is found that it belongs to a certain genus and that several specific epithets have been applied to it. In most cases the first specific epithet under which it was described is the valid one, even though it was not originally placed in the correct If the plant was first named correctly as to both genus genus. and species, the name of the author follows without parentheses. For example, Linnaeus correctly applied the name Lilium canadcnse L. If, however, a botanist when naming a plant placed it in the wrong genus, the error must later be corrected, in which case it will retain its earliest valid specific epithet when changed to the proper genus. The name of the one who first gave the specific epithet (in the wrong genus) will follow in parentheses and the name of the one who first gave the correct generic and specific Mertensia combination will come afterward, not in parentheses. virginica was first called Pulmonaria virginica in 1753 by Linnaeus, and in 18 U> de Candolle showed that it belonged to the genus A few Mertensia, hence the name Mertensia virginica (L.) DC. other examples will serve to show how specific synonymy is cases the latter should be followed also, as
Portulaca oleracea L. var. saliva
1
determined. 1. Linnaeus' 'Species Plantarum' in 1753 gave the name Glecoma hcdcracea to a plant. In 1834 Bentham named the same species NepetaGlechoma, and in 1888 Britton, Sterns, and Poggenburg named it Ncpeta hederacca. Linnaeus was the first to give it a legitimate specific name, and if he placed it in the correct genus, its name should stand as Glecoma hedcracea L., and those proposed later should become nonvahd synonyms. This 2. In 1824, Bigelow named a species Lacluca integrifolia. in Nuttall had for 1818 be to a proved homonym, however, This different a name to the same species of species. applied NuttalFs is now correctly known as Lactuca pulchella, and thereNeverthefore Lacluca inlegrifolia fe a nonvalid synonym for it. it was before to Lacluca it was because applied pulchella less, 1
By agreement
botanists do not go back of Linnaeus' 'Species Planin the publication of names, and for
tarum' (1753) to establish priority some of the groups of lower plants (see p. 230).
later dates of priority
have been
set
228
A TEXTBOOK OF SYSTEMATIC BOTANY
applied to Bigelow's species, it cannot be used for the latter, or indeed for any species. For this reason Ellis proposed a new name, Lactuca sagittifolia, for the species that Bigelow had incorrectly named Lactuca integrifolia. 3. In 1828, Nuttall called a plant Nuttallia involucrata but did not give it a specific description. This name, therefore, was a hyponym (nomina undo) and nonvalid. In 1838, Torrey and
Gray named the plant Malva involucrata. Ten years later Gray decided that the plant belonged to genus Callirrhoe. Its correct name is therefore Callirrhoe involucrata (T and G.) A. Gray. ' 4. In 1753, Linnaeus' Species Plantarum' gave the name Arnica montana var. alpina. In 1799, Olin and Ladin did away with the trinomial by giving the varietal name a specific value, is now known as A. alpina (L ) Olin and Ladin. They were not required to use the name alpina, however, since varietal names are not protected by priority.
and the plant
EFFORTS TOWARD UNIFORMITY Realizing the confusion that is produced by the use of nonvalid arid the uncertainty as to what should constitute validity, botanists have made repeated efforts to reach a common basis.
names
These efforts have taken the form of comprehensive publications, ' Genera Plantarum' and 'Species Plantsuch as Linnaeus' arum' and Bentham and Hooker's 'Genera Plantarum,' and meetings have been held to establish principles and rules governing nomenclature. Botanical Congresses.
Linnaeus in 1751 proposed a few rules
Since that time the number dealing mostly with generic names. of congresses, national and international, that have been held to
reach agreements on nomenclatorial and taxonomic procedure has been much greater than is generally realized. 1 The Paris International Congress. In 1866 a group of eminent taxonomists met in London to discuss ways and means of standNo rules were formulated but ardizing botanical nomenclature. French the authorized taxonomist, A. P. d6 Candolle, to they draw up a set of rules of botanical nomenclature and present them As passed by to a congress to be held in Paris the following year. that congress, they were made up of principles, rules, and proce1
See Herbert C. Hanson, Codes of Nomenclature, and Botanical ConAmer. Dot., 21, 114-120, 1925.
gresses,
NOMENCLATURE
229
dures 1 that were highly constructive but conservative and consisted mostly of those that had been tried out and found satisfactory.
Arbitrary and untried regulations were wisely avoided. The following provisions, among others of less significance, were adopted: (1) A plant can have but 'one valid technical name. (2) A species is not named unless its specific name is assigned to a genus. (3)
The name must be accompanied by a
description, or other
means
with date. (4) Two different species, or other (5) Generic and specific groups, cannot bear the same name. combinations should be followed by the name or names of their The Paris Code, as it has been called, also clarified and authors. of identification,
some extent
to
unified the use of categories for
taxonomy and
threw strong emphasis on the desirability of Latin names. While criticism has been made of some of the provisions of the Paris Code (not those given above), it has had a great permanent value, and it became the basis of all work of this kind that followed
it
at later congresses.
The Vienna International Congress. In 1905, after the Paris Code had been given a thorough trial, the second International In general the principles and Botanical Congress met in Vienna. rules of the Paris Code were readopted, but many slight changes in wording were made as a result of experience in applying that code. The Vienna Code made the following notable changes: use of Linnaeus' 'Species Plantarum' (1753) as a The (1) beginning point for priority of names was limited to vascular plants. (2) Recognition was given to Linnaeus' 'Genera Plantfifth arum/ edition, published in 1754, for generic names. 7
(3) Names that had been rejected for certain reasons could in the future be applied as new names to other groups. (4) Any new name was to be nonvalid unless a Latin diagnosis or description of the group was published with it, this provision to go into effect (5) A list of nomina conservanda, or names 1, 1908. retained although not valid under the rules, was authorized. These were mostly generic names that had come into prominent
January
use either before the adoption of the Paris Code or in violation of Unfortunately, the list of such names was large and adopted hastily, and the selection was not based on the mature judgment
it.
No pro-
of a representative group of botanists from all countries. vision was made for adding to the list when older obscure 1
For the English translation of the rules
63-77, 1868.
in full, see
Amer. Jour,
names Set.,
45:
A TEXTBOOK OF SYSTEMATIC BOTANY
230
are found, which, by a strict application of the rules, would invalidate names in general use. The code was published in
French, English, and German. The Brussels Congress. In 1910, the third International Botanical Congress met at Brussels. By this time it was realized that, since Linnaeus had given relatively small attention to the lower plants,
it
would be wise to use the work
of other
men
specializing in these groups as beginning points for establishing This the Brussels Congress did, 1 and priority in some of them.
made minor improvements in the wording of several of the Vienna Congress. The two were published jointly in 1912 (see page 312) and became known as the International
it
also
rules of the
Rules.
American Contributions. The American botanists working through the botanical section of the American Association for the Advancement of Science have long taken a progressive attitude toward unified nomenclature. At a meeting in Rochester, New York in 1892 they set up a code that emphasized priority in '
determining the validity of names and specified Linnaeus' Species Plantarum' as the starting point for such priority. In 1903, this organization appointed a nomenclature commission, which, at a meeting in Philadelphia in 1904, approved a code for submission to the Vienna Congress. It introduced the 'type concept/' which is, briefly, that each species shall be based on a type individual, each genus shall be based on a type species, This idea was rejected by the Vienna Congress. In protest etc. against the nomina conservanda, as adopted by the Vienna Conand the requirement of a Latin diagnosis to accompany the
gress,
names
of
new
groups,
and because
of the cold reception given to
In these rules the starting points for priority for the specific names of the different groups of plants were as follows: For Spormatophyta, Pteridophyta, Sphagnaceae, Hepaticae, Lichenes, Myxomycetes, and Algae ' Species Plantarum' (1753). (with the exceptions given below) Linnaeus' 1
For Musciniae, Hedwig's 'Species Muscorum' (1901). For Nostocaceae Homocysteae, Gomont's 'Monographic des Oscillariees' (1893-1899). For Nostocaceae Heterocysteae, Bornet and Flahault's 'Revision des ' Nostocacees (1886-1888). For Desmidiaceae, Ralf's Heterocystees 'British Desmidieae' (1848). For Oedogoniaceae, Hirn's 'Monographic und Iconographie der Oedogoniaceen ' (1900). For Uredinales, Ustilaginales, and Gasteromycetes, Persoon's 'Synopsis Methodica Fungorum' ' For other fungi, Fries' 'Systema Mycologicum (1821-1832). (1801). For all fossil plants, the date 1820.
CHAPTER X PRINCIPLES OF
TAXONOMY
In Chap. I the reasons for making a knowledge of evolution the basis of a working system of taxonomy were shown. Many principles have been developed to aid in applying this knowledge
taxonomic systems in both the plant and the tracing of the progress of evolution and the application of it to the classification of existing plants and animals have been a challenge to the minds of some of the greatest scientific men for many years, and the work is far from finished. to the building
up
animal kingdoms.
of
The
DIFFICULTIES IN CLASSIFICATION
The
some hundreds of thousands of different an enterprise of great magnitude and great Even if we were content with an artificial classifidifficulty. cation that merely placed together plants and groups that resemble each other, much work would be required; but when we classification of
kinds of plants
aspire to
make a
is
show
classification that will
encountered are times almost insurmountable.
ships, the difficulties
all
much
genetic relation-
greater
and some-
greatest problem in plant taxomony is this: There are now of living species the relationships of which we thousands many wish to establish through genetic lines; but the memory and the records of man are so short that they do not show direct evidence of ancestry, and we have to rely on our own reasoning power to construct the genetic lines leading from the distant past to these The evidence we have consists of scattered existing species. fossils, the relationships of which are based on human judgment;
Our
morphological similarities that are open to varied interpretation;
and our own evaluation of all this indirect evidence. Figure 92 shows the magnitude of the problem and offers, in part, a solution of
it.
It
seems certain that 'the
simple
first
celled green alga
and capable
life
must have been very
much
simpler than a one-
form of
undifferentiated protoplasm of living
237
and reproducing
itself in
an
238
A TEXTBOOK OF SYSTEMATIC BOTANY
Schizomycetcs (Sapr. &par.) Bacterial line
Schizomycetes (Autophytic)
Cyanophyceae
Myxomycetes Flagellate line
/
Flagellata
Brown
Oomycetes
algal line
Phaeophyceae
Basidiomycetes /

Red
algal line
/
Rhodophyceae Ascomycetes
Zygomycetea
Green
algal line
Chlorophyceae
Musci wort line li Liverwort
/
Hepaticae
Pteridophyta
(Club mosses) Pteridophyta
(Ferns)
Gymnoapermae Angiospermae
FIG. 92. Suggestive relationships that may exist between groups of plants, past and present. Solid lines are based on stronger evidence than broken lines. (From 'Plant Life,' D. Van Nostrand Company, 1942.)
From it the entire organic world seems inorganic environment. to have evolved, but discovery of the steps in the process challenges the best efforts of the human mind. Our efforts at plant classification have met with difficulties: (1)
two
practical
the magnitude of the problem because of the
num-
PRINCIPLES OF TAXONOMY ber of species, and
(2)
239
the difficulties brought about by loss of
ancestral forms.
Due to Scope of Subject. The pioneers in any submake some mistakes, and early systematists were no excepThe magnitude of the work was so great that, with no tions. organization among themselves and no governing standards, Difficulties
ject
they labored at a great disadvantage. The Logical Procedure. If all the taxonomic work were to be done over again, the logical procedure would be to assign different parts to different workers who would confer from time to time in order to coordinate the units into a harmonious whole. Plant classification began, however, when science was in its infancy, and such an organization was not even dreamed of. Clearly the undertaking was too great for one man or one generation. None of the earliest botanists had a vision of the entire enterprise, and none could have carried it through if he had. Furthermore, the
early work was purely voluntary and done mostly by men who carried a heavy load of other duties, or who had other interests
and used botany as an avocation.
Work Done Piecemeal. The natural procedure was followed. Each man studied the group of plants that happened to attract him, but many groups were neglected. Most of our best taxonomic work has resulted from group specialization. Naturally, those plants that were conspicuous or had an obvious economic When later botanists significance received the most attention. with a broader vision attempted to summarize the results and record them in more general systems of classification, they encountered several difficulties. In the first place, many of the plants had been left unclassified, so they had to be placed in heterogeneous groups for further study or tentatively attached to groups where they did not belong; and in the second place, the better known groups had been classified
by
different methods,
from
different viewpoints,
and by use
of
Some groups were
so poorly constructed that they had to be entirely rebuilt, others were more or less The modified, and still others were used in an imperfect form. different characters.
result is our present system of classification, weak in others and not well coordinated.
Restrictions of Travel.
There
floras of different countries.
is
good
in spots but
a good deal of variation in the
Botanists have never been able to
A TEXTBOOK OF SYSTEMATIC BOTANY
240
enough to compare all these different floras, and this diffiwas far greater in the early days than now. As a result, classifications have been made up on too limited evidence.
travel
culty
Herbaria with representative specimens from different countries and habitats have improved the situation to some extent, but most herbaria are very fragmentary. Limited Publication. seeing pictures of
them
The next
best thing to seeing plants
or reading
is
and hearing about them.
of our classification was made when botanical journals were unknown, and the meager writings in one language were little read by those speaking another. Many species that had been discovered and named were rediscovered and given other names by those unaware of the previous work. The whole effect of the lack of intercourse and travel was to burden the tentative schemes of classification with duplicate names, synonyms, faulty descriptions, and a confusion of tongues.
Some
Difficulties Inherent in the Subject Matter. classification
one.
was
When we
The
desire for a
before the machinery was ready for making began to classify plants, we had no intimation of felt
little knowledge of physiology or morpholno for aiding the eye in a study of tiny and microscopes ogy, plants and the detailed structure of larger ones. Pre-evolutionary Classification. Prior to the work of Darwin, the viewpoints of classification were quite different from those that prevail today. Then there were two methods more or less One was to group plants according to economic uses, and used. the other to group them according to gross similarities in appearance. No attempt was made to work out phylogenetic relationfor none were known to exist. Attention was given to the ships, description of species, for each species was assumed to have been
evolutionary origin,
created separately; hence relationships of individuals within each species were recognized, and to some extent species were grouped into genera. Some even spoke of ' natural affinities ' an rather of uncertain expression meaning.
Some
quite elaborate systems of classification had been probefore the doctrine of evolution was set forth. These posed the were more or less phylogenetic viewpoint, systems, lacking
upon morphology as an index to phylogeny that the classifications of de Jussieu, de Candolle, and Endlicher (see Chap. XI) had much in common with those of
artificial,
but
it
reflects credit
PRINCIPLES OF TAXONOMY
241
Doubtless these could have been improved by further morphological study even without a knowledge of evolution. The realization of the evolutionary origin of species has necessitated considerable readjustment of the older systems but not a
today.
complete revolution.
Chiefly
reclassification of the
more
it
has served as a guide in the
difficult parts of
the plant kingdom
where purely morphological characters had not been fully comprehended and interpreted. It has given a wholly new significance to comparative morphology. Late Invention of the Microscope.
Had
the microscope been
in general use throughout the
development of botanical science, the lower plants would not have been so long neglected. Most of the older classifications either ignored these smaller forms entirely Lack of the microor threw them into chaotic, unsorted groups. scope also delayed the discovery of complex life histories that have been found so significant in the fungi and even in such large plants as ferns
Loss
and angiosperms. Forms. It is not too much to say that
of Ancestral
t(
miss-
'
ing links represent the rule rather than the exception in all studies We do not even know how of the phylogcny of plants and animals. of occurred to make our presinstances algal degeneration many
ent-day fungi, or the transitional forms between the green algae Paleobotany has done much, to be sure, but it is incomplete, with many gaps, and the chronological sequence is only approximate. If we had a record of all ancestral
and the angiosperms.
forms,
it
would solve most
of the difficulties of phylogenetic
taxonomy. Degeneracy resulting in simplification is sometimes hard to This fact has been distinguish from primitive simplicity. troublesome in placing the bacteria, the yeasts, the Fungi Imperfecti, and even some of the flowering plants, e.g., the grasses, and some deciduous trees (see page 205). A Rigid System for a Flexible Subject. The English botanist,
John Ray, at the beginning
of the eighteenth century, anticipated ' the feelings of many later botanists when he said, Nature refuses Notwithstandto be forced into the fetters of a precise system.' and we make our definite this groups try to fit plants dictum, ing
into them.
As
yet,
we
see
The chief difficulty As shown later in this
no other way.
comes from intergrading characters. chapter, most of the major characters are not intergrading.
If
A TEXTBOOK OF SYSTEMATIC BOTANY
242
they were as troublesome in this respect as certain minor characters, it is doubtful if our present system of taxonomy would be workable. Most of the controversies of modern taxonomists are due to four causes: (1) differences of opinion as to which forms of organs and structures are primitive and which are more advanced; (2) differences of opinion as to the relative value of characters for purposes of classification; (3) intergrading characters; and (4) unwillingness to sacrifice mechanical convenience to phylogenetic
principles.
Of the difficulties presented here all can be overcome but two: the loss of ancestral types and the making of hard and fast Paleobotanical categories where characters are intergrading. studies will help to relieve the former difficulty studies the latter, for some of the gradations, not
and all,
ecological are merely
the effects of environment.
BASES OF TAXONOMY Probably the most interesting scientific aspect of systematic botany is the determination of phylogenetic relationships. They present a record of the products of evolution modified by geological and climatological agencies. Phylogeny is, however, a most difficult subject, for many of the evidences have been effaced. If we had a written record of all the forms of life on the earth from the beginning to the present time, the phylogeny, of any group could be derived by sufficient study, but in the absence of such a record we have to resort to more or less indirect evidence, which will
be discussed
later.
In all studies of phylogeny the origin and individuals by evolution is assumed as axiomatic, for if there had been an independent creation of each species, Once we there would have been no relationships between them.
Phylogenetic Evidences.
of groups
accept this doctrine, then, our problem
is
to trace the relationship
of existing individuals and groups back through their ancestry, most of which has long since disappeared leaving only a few
scattered fossils
and other
traces.
Until recently our knowledge of phylogeny in plants was based chiefly on three lines of research, comparative morphology, anat-
omy, and paleobotany.
number
These are now being supplemented by a
of others, including ecology, plant geography, cytology,
PRINCIPLES OF TAXONOMY and serum
genetics,
diagnosis,
243
which are discussed
later in this
chapter (page 259). All modern tendencies are toward making phytogeny the underlying principle of taxonomy, but phylogeny is not in itself a tangiWe must, therefore, have ble thing that appeals to the senses.
by which to determine phylogenetic relationships. Morphology as an Indicator of Relationships. The close
usable criteria
similarity of certain plants to each other appealed to the early botanists long before the concept of evolution was developed.
were, therefore, fairly well prepared for this new idea and diligently set about applying their knowledge of morphology to few laws gradually took form to aid them, its interpretation.
They
A
life has usually advanced from the simple to the complex (progressive development) but has sometimes been
principally (1) that
or loss of parts (regressive developthat the simpler forms of life now existing are more like their ancestors than the complex ones (though not exactly the
by degeneration
simplified
ment)
;
(2)
HaeckePs law
of recapitulation, that ontogeny is a phylogeny; (4) Dolle's law of irreversibility in evolution, that a product of evolution never goes back to an ancestral condition; and (5) that homologous rather than analogous structures indicate relationship. To these laws have ' recently been added the morphological indicators of phylogeny' set forth on pages 276 to 280. Both in animals and in plants morphology is the most widely used instrument of classification. This was true before the time
same);
(3)
brief repetition of
of
it is true today, though we now use the light of our knowledge of evolution.
Darwin and
gently in
to be useful accurate.
through
must be
Genetic
similarities
fairly easy of application
it
more
An
intelli-
indicator
and reasonably
relationships usually express themselves differences in form and structure. These
and
numerous, and considered almost endless combinations. Also, collectively they present the to differences appeal eye, usually on brief morphological of a means classification. and offer rapid Practically inspection, different characters are in themselves
herbaria, all systems of taxonomy, and all botanical manuals are based almost entirely on comparative morphology and anat-
all
omy; and even though the newer experimental methods of cytology, genetics, and ecology may throw light on the mechanism of evolution (see page 19) and on phylogeny in the lower
A TEXTBOOK OF SYSTEMATIC BOTANY
244 categories
genera, species, subspecies, etc. (see page 262) they if ever, entirely replace the older taxonomy based on
cannot soon,
That the experimental method will amplify the morphological, help to explain it, and correct some of its errors there can be no doubt. Morphology does not suffice, however, in certain groups of lower plants, particularly those morphology and anatomy.
pathogens
in
which similar-looking fungi or bacteria cause
different diseases, thus indicating a difference in their species. is It a somewhat unsatisfactory indicator in the Fungi
Imperfecti, where only asexual reproduction remains in plants once possessed of sexual stages of various kinds. For example, Fusarium is a form genus based on the appearance of the conidia, but conidia of similar appearance are known in different genera of
well-known Ascomycetes. Difficulties in Applying Morphological Indicators. Throughout the Christian Era up to the twentieth century there was an accumulation of morphological data far beyond the ability of
made to the point of placing or less well-defined species, genera, crude attempts also were made at classes and
botanists to interpret.
many and
of our plants in
families.
Some
Progress was
more
divisions, resulting in such groups as thallophytes, fungi, and seed plants, quite different from the carefully constructed phyla that
some have
since proposed.
For the most
part,
classification
prior to the twentieth century took this form: that certain genera were believed to constitute a certain family (often called an order), certain families to constitute a certain class, etc., but
how
the smaller groups should be arranged within the larger
was undetermined.
One of the difficulties in using the accumulated mass
of
morpho-
logical data for phylogenetic purposes was lack of knowledge of major and minor characters (see page 264), and there is still some disagreement in this field. For example, the distinction between woody and herbaceous plants was given great prominence up to the middle of the eighteenth century, was then relegated to a minor position, but in 1926 was revived again by J. Hutchinson 1 in a more scientific form based on anatomy and histology as well
as on external form is
and general
texture.
Its relative
importance
again a matter of controversy. 1
'The
Families of Flowering Plants,' Macraillan
London, 1926.
& Company,
Ltd.>
PRINCIPLES OF TAXONOMY
245
Another difficulty lay in determining which of two forms of an organ was the more primitive and which the more advanced e.g., separate versus united petals, persistent versus deciduous leaves, and one versus two cotyledons. On this subject a summary of our present usage is given on pages 276 to 280. Internal Anatomy as an Indicator of Relationship. The difference in stem structure between monocotyledons and dicotyledons has long been recognized, the former having scattered fibrovascular bundles and the latter having bundles arranged in a cylinder enclosed by a cortex and surrounding a pith. Later, differences were noted in the leaf traces branch bundles running out into ;
the leaf petioles and floral parts and, in the dicotyledons especially, differences were observed in the details of secondary
thickening of stems by the addition of more phloem and xylem. fact that some trees have heart- and sapwood while in others
The
there
is
no such distinction has been known
for centuries.
Histological differences in the xylem have also been observed, xylem vessels (tracheae) in the angiosperms replacing the more primitive tracheids of the gymnosperms and tyloses being
formed
in the old vessels of
some woody
species but not others.
Recently, finer distinctions in the character of the wood, especially the size and walls of the xylem cells, have been studied to the point where keys for specific identification have been made on wood structure alone, 1 with no reference to external morphology.
Evidence dealing with the identification of woods by microAnatscopical examination is now accepted in criminal cases. where and reliable indicators of are histology relationship omy they are applicable, but they are more time-consuming than morphological observations, and there are many species of herbaceous plants in which they have not received special study.
Physiology as an Indicator of Relationship.
It is
a well-known
fact that groups of plants differ more or less in their physiology. These differences may be either qualitative or quantitative and may or may not be accompanied by morphological differences. If Physiology, however, is a cumbersome basis for classification. we had to perform a series of physiological experiments to tell one
from another, progress would be slow. It would be very tedious, for example, to establish families on the basis of the comspecies
1
See Samuel
$ons, Inc., 1934.
J.
Record, 'Timbers of North America,
'
John Wiley
&
A TEXTBOOK OF SYSTEMATIC BOTANY
246
pounds of nitrogen in the soil that are best suited to their use as food materials. Furthermore, the usual physiological processes, especially among chlorophyll-bearing plants, are not established as dependable criteria of species. It is doubtful whether families constructed on a basis of nitrogenous food requirements would show phylogenetic relationship. In many cases they are too unstable, for in response to changes in environment, heat, light, food, moisture, etc., plants
show changes
in physiology
much
more
For this reason physiological readily than in morphology. differences are little used except to supplement morphological ones, as in the lower groups just mentioned where the latter alone are not sufficient. It seems unwise, however, to rule out physi-
ology entirely, as some systematists have been inclined to do, especially as serum diagnosis (see page 247) is really an interpretation of a physiological reaction. Such an attitude has the effect of discarding a tool that is sometimes useful, especially in classifying bacteria and fungi.
Paleobotany. Morphology of existing forms of plant life gives incomplete evidence of phylogeny because of the many ancestral forms and connecting links that have long since disappeared.
Some
of these
have been preserved as deposits and recognizable
fossils.
There is evidence that the first life began in the sea, which at that time covered nearly all the land and was not so salty as at present. Probably the first forms were so delicate and so scattered that they left no remains that can now be detected. Later, the more abundant and substantial forms left deposits of graphite
and carbonates, but the cellular structure was quite obliterated. plants and animals with more solid portions, skeletons, heavy cell walls, etc., dying in localities favorable to their preservation, became covered with earth, and a few of them have been recovered as fossils. Doubtless many more are still hidden. Some of these fossils are merely impressions of the plant part on Still later,
plastic material that later
hardened into rock, while the plant Others consist of plant parts replaced quite disappeared. bit by bit with mineral The slow molecular replacement has produced the best fossils, for in them even the cellular structure is itself
often preserved, sometimes quite faithfully. The great value of these fossils lies in their chronological history of ancestral forms, ' missing links ' in evolution, and in their
PRINCIPLES OF TAXONOMY record of evolutionary morphology
ment
247
the sequence in the develop-
Most fossils represent extinct species that are, Others correspond to species nevertheless, named and classified. that still exist practically unchanged. In numerous cases fossil of organs.
records have confirmed or corrected opinions based on the morphology of living plants as to the relative antiquity of existing groups, thus showing the trend of evolution. Through the researches of historical geology the strata of the earth's crust have classified, the method of their formation determined, and with some approximation their ages have been estimated (see frontispiece). Through a combined study of geology and paleontology the climates on the earth at the different periods and the effects of these climates on the forms of life existing at those times
been
page 12) are known to some extent. It is probable that the phyla of plants and animals originated during profound and disastrous climatic and geological changes that exterminated (see
different
Vicissitude begets hardy races. species. Unfortunately, the paleontologies 1 records are very fragmenWhile they have yielded much of value and have modified tary. and supplemented somewhat our interpretations of present-day
many
morphology, they have left much unsaid. The softer plants, such as green algae and liverworts, usually failed to leave a recognizable impression, and even most woody plants decayed and disappeared entirely except under the most favorable conditions We do not even have a for preservation, such as burial by mud. record of the evolution of flowers from the ancestral sporophylls; for although both sporophylls and flowers have been fossilized,
Much is hoped for in the future, transitional forms are lacking. for in all likelihood man will continue to find and interpret fossils many Serum
for
centuries.
Diagnosis. An important physiological or chemical indicator developed to show phylogenetic relationships is the serum diagnosis of Carl Mez, of the University of Konigsberg, and
When it is desired to determine the one kind of plant to another, the proteins of the two are compared, those with proteins most similar being interpreted as most closely related. To this end a protein extract is made from one kind of plant and injected into the body of a After waiting a suitable time for the rabbit's body to rabbit. his associates
and students.
relationship of
react to the protein,
its
blood
is
drawn and the serum
is
mixed
248
A TEXTBOOK OF SYSTEMATIC BOTANY
Zoatereaceae
^~ ^
oceaceag,
Hydrocharit
Ranunculaceae FIG. 93.
Phylogenetic arrangement ot the monocotyledons as indicated by
serum diagnosis.
(Redrawn
after
Ankermann.)
with the protein extract of the second kind of plant. If a precipIf such a precipitate forms
itate forms, relationship is indicated.
when a high
dilution of the
A
serum
is
used, the relationship
is
con-
than forms only with serum that is less diluted. remarkable phylogenetic tree has been constructed on the
sidered closer
if it
PRINCIPLES OF TAXONOMY results of these reactions, one
branch of which
is
249
shown
in Fig. 93.
The
relationships thus indicated generally, but not always, correspond with morphological conclusions, and it is noteworthy that the phylogenetic lines form a branching, not a reticulate, system and thus conform to rule 1 of the principles on page 277. The Mez, or Konigsberg, serum diagnosis must be looked upon as a valuable supplement to morphological studies for the determination of relationship, although the work needs much verification and has not always been found reliable.
PLAN OF TAXONOMY
Taxonomy must be looked upon as an attempt to determine the relationship of plants by studying tti3ir similarities ences and thus to build up a system of classification. of
man
and
differ-
The mind
cannot comprehend each separate individual of the
millions of plants on the earth; hence it is necessary to think of them in groups, generalizing their characters in so far as it is safe
to do so. This necessity and the tendency of the scientific worker to be orderly have led us into many of our taxonomic problems. As a result of centuries of study and discussion, botanists and
have learned much that is essential to logical classifiand the two branches of biological science use essentially the same plan. Probably the work of Linnaeus, who named and classified both plants and animals, contributed something to this uniformity. There is now a pretty general agreement on the main principles and a fair uniformity of practice except in certain Each kingdom is details, where some difference still exists. subdivided into great groups and these into smaller groups until zoologists
cation,
the species is reached, the species being a collection of individuals In some species even lower categories that are essentially alike. are recognized.
CATEGORIES USED IN TAXONOMY
The term
'
7'
category
is
used to designate a group of any which plants or animals are
definite rank, large or small, into
Classes, genera, species, families, etc., are examples. Categories must be made to fit plants, as plants cannot be
classified.
As a forerunner to the categories we categories. now have, certain group entities were noted many years ago. Some of these were small groups; others were large, including changed to
fit
A
250
TEXTBOOK OF SYSTEMATIC BOTANY
these small groups and additional ones. Thus the flowering plants were thought of as a very large group including legumes,
mints, umbellifers, daisies, etc., and legumes were known to include various kinds of clovers, vetches, peas, etc. Centuries of
study yielded a mass of information about groups of plants, and we have attempted to make usage more uniform by adopting the system of categories given below. Always we must think of them as man-made attempts to simplify and express a complex, unstandardized, and constantly changing mass of living things. For convenience and uniformity a rather definite series of The regular categories for the plant kingdom has been adopted. categories, ranging from the largest to the smallest, are as follows :
kingdom, division, class, order, family, tribe, genus, and species. These terms have each been given as definite a meaning as possible, and they must not be used loosely or interchangeably.
Most categorical names have, for convenience, definite endings. The names of all groups larger than genera are given the plural form. The names of orders usually end in -ales, those of families The following is an example in -aceae, and those of tribes in -eae. showing the sequence
of categories to
which the rose belongs and
the proper endings.
Division Spermatophyta Class Angiospermae
Order Rosales Family Rosaceae Tribe Roseae
Genus Rosa Species rugosa
In special cases the qualifying prefix 'sub' may be added to any of these, as subclass, subgenus, etc. This practice is for convenience where the group is a large one containing many members and especially where these members fall into two or more natural For example, the great class Angiospermae is commonly groups. into divided two subclasses, monocotyledons and dicotyledons.
Some botanists, however, carry this practice too far and make suborders, subfamilies, or subgenera where the evidence to justify it is trivial or debatable, and some create confusion by using the term ' subfamily' for groups that others call tribes. There
is
no uniformity
in size
among
the categories.
One
PRINCIPLES OF TAXONOMY
251
genus may contain dozens of species and another only one or two. Except to satisfy a desire for uniformity of procedure, several For categories might have been omitted in the smaller groups. example, the family Adoxaceae has only one species, Adoxa Moschatdlina. If all families had been as small, or even contained but a half-dozen genera, probably families and tribes would never have been devised, and orders would have been divided directly into genera, or there might have been families with no orders or tribes. In actual practice, tribal names are not often used except in the larger families, and the ordinal names of the higher plants are omitted from many of the manuals of this country.
What
Constitutes a Species.
meaning there must be a starting order
is
To
give categories a definite To say merely that an
point.
a collection of related families, each of which
is
a collec-
tion of related tribes or of genera, does not give a full comprehenMost authorities look upon sion of the meaning of these terms.
the species as the unit of classification and then build the higher Others prefer to consider the categories upon this conception.
genus the unit.
As most
species are
made up
of individuals so
nearly alike that no need has been felt for a finer subdivision, it best suits the majority of botanists to use the species as the classification unit, subdividing it into subspecies, varieties, races, etc., only in those species where such a procedure serves a useful
purpose.
One
of the
most troublesome problems
in
taxonomy
is
to arrive
The quesat a definition of a species upon which all can agree. tion of defining a species is so perplexing that it has been made the subject of several research papers and at least one symposium. There are two older conceptions, each having a considerable Certain botanists, notably de Candolle, Linnaeus, following.
and Gray, constructed their species along bold and clear-cut lines, each species being separated from its relatives by distinct and Trivial differeasily differentiated morphological characters. that were those were ences only matters of ignored, particularly In some of were shown. minor characters in which the degree Linnaeus' species the different individuals showed considerable minor variation. In others they were essentially alike. Linnaeus' species lacked uniformity of character, however, because some of his work was compilation based on plants he had never
A TEXTBOOK OF SYSTEMATIC BOTANY
252
This broad method of species making reached its greatstudied. est perfection in the work of Asa Gray. By his usage the number of species was kept relatively low, and identification of plants to
was comparatively easy. The expression 'Linnaean has come into accepted use for these bold, easily distinguished groups with clear-cut characters, and it will be used ' here, although 'Grayan species may be a more accurate term. Some taxonomists follow the arbitrary rule of insisting that at least two morphological differences be required to separate one the species '
species
species
from another.
The other conception was that
'
'
or elementary species It is practically true that no two individuals 'primary species/ In an elementary species the individuals must are exactly alike. be as nearly alike as though they had the same pure line parentThis idea involves the necessity of making separate species age. of all plants showing any constant differences whatsoever, no matter how trivial or minute; and in some species so made the differences are not even constant, single specimens of unknown of
7
lineage,
some
of
been given new
ecological modifications, having
names.
It will be readily perceived that extensively carried out, would vastly increase the Draba verna L. is cited as an of species to be dealt with.
this plan,
number
them merely
specific
if
example of a species of the Linnaean and Grayan kind that could be divided into more than 100 elementary species. Where intergrading characters are found there may be almost as many elementary species as individuals. Such a system becomes burdensome and detracts from the usefulness of taxonomy. Furthermore, where 'species splitting' has been carried to such extremes, as in the genus Crataegus, the specific distinctions are so hard to follow that only the specialist in that group can carry on
the identification.
One taking an impartial view of the this conclusion: that for
most
species question is forced to of the plant kingdom the bold
Linnaean type of species is simpler than the finely divided elementary species and serves every essential purpose; but in certain groups it may be necessary to make finer distinctions for research reference, though even there the majority of botanists may not need to do so for their more general work. The natural answer is the assembling of the individuals into relatively few, large, clear-cut species and, where necessary, having additional
PRINCIPLES OF TAXONOMY
253
be used only by those who have special need Various terms have been used to designate these finer divisions, such as subspecies, varieties, races, types, and forms. To be sure, this introduces the trinomial nomenclature; but it this is cumbersome, it has the advantage of showing relationship, for the specific name connects the related subspecies to each other. Species making as done in the past has been based on simple fine distinctions to
for them.
inspection of individual plants.
Geneticists
and
ecologists are
working on a more exact, experimental method, which, however, requires extensive research on each species (see page 202). The Newer Species Concept. The conception of a taxonomic species given above is the classical one that has been in use for There is a centuries, starting even before the time of Linnaeus. newer species concept, based on genetics, cytology, and ecology in addition to the conventional morphology and geographical disIt aims to be a more tribution, that has a more scientific basis. objective concept to have a broader foundation of facts and hence to enable one more clearly to visualize what natural units have evolved. It will be explained here, even though it has been applied to relatively few groups of plants as yet, and its universal It merapplication must await an immense amount of research. its our attention because the results of its use up to the present time suggest that it will prove of wide application, and its methods must be taken into increasing consideration by all taxonomists.
This newer conception is based on experiments that indicate that natural systematic units are kept apart, and successful crossThe ing is prevented by barriers of various sorts and degrees.
found separating different species within the studied be can experimentally, whereas those more progenus found ones that separate genera and the higher groups do not lend themselves to such analysis. Two kinds of barriers are found: internal (hereditary) and If there were no barrier to block free external (environmental). and intercrossing migration, all the members of one genus would belong to a single species. This is the case in a few genera. In most instances, however, hereditary and environmental barriers The are operative to separate both species and lower units. barriers that are
hereditary barriers to successful crossing may involve the number or structure of the chromosomes, or they may be primarily gene-
A TEXTBOOK OF SYSTEMATIC BOTANY
254
chromosome number
in plants that reproduce sexually almost always indicate that different species are involved, according to this concept, because this is a formi-
controlled.
Differences in
dable barrier to successful hybridization. Rearrangements in chromosome structure may likewise render forms wholly or partly if such are formed, being victims of their own inherent weakness or of a hostile environment. The various genetic barriers often take the form of incompatibilities or inherited weaknesses that tend to eliminate the hybrid Both morphological offspring and maintain the pure units. characters and physiological functions, such as growth and The environmental barriers are either flowering, are affected.
intersterile, the resulting offspring,
geographic or ecologic. Under this concept species of the same genus are separated The species may be unable to primarily by genetic barriers. all if their genetic isolation is complete. If it is but they may produce hybrids which are partially sterile or which produce a weakened second generation not as well fitted to survive in nature as the original parent species. A few instances have been discovered in which plants are found to be entirely intersterile, and it is impossible to link them through crossings with an intermediary, yet they cannot be
hybridize at partial,
distinguished morphologically. Biologically, these are distinct in in which genetic differentithese rare cases species. However, ation has preceded the morphologic, good taxonomic practice dictates that the forms be retained within the same taxonomic species.
The cross
experimentalists are finding that species that are unable to may or may not occupy the same environment, while those
At those places hybrids between them
that can cross grow largely in different areas.
where their ranges
of distribution overlap,
are also to be expected.
If species
that can cross, even though
with only partial success, occupied the same range, they would soon lose their identities through hybridization. The subdivisions of species, such as the subspecies, variety,
when the opportunity but they are separated by environmental isolation. This isolation seems to be almost always geographical, and it is thought to be maintained by natural selection, i.e., adaptibility to the environment or the lack of it. Correlated with the environrace, etc., are able to interbreed freely offers,
PRINCIPLES OF TAXONOMY mental
isolation,
there
may
be characteristic differences
255 in
appearance. This newer species concept attempts first to work out the stages of evolutionary differentiation found in nature and then to assign ranks to the groups recognized. Some transitional stages are found that are, for instance, neither species nor subspecies, thus
Few reaffirming the idea that evolution is a continuous process. students are in a position to follow the exhaustive experimental called for to apply this concept with complete assurance. Nevertheless, the work to date stresses the significance of geographic and ecologic distribution and of chromosome numbers to
program
data not out of reach to most workers. it is very difficult, if not impossible, to apply the new definitions, before actual experimental work is done, to the thousands of species of plants that have long been recognized. Fortu-
taxonomy
Of course,
nately, however, the species of the experimentalist is frequently identical with that which has been carefully worked out on the This means basis of comparative morphology and distribution.
that the
but
new methods
will
will amplify, stabilize,
not overturn our existing classification and clarify the position of the system-
and help to explain how new species arise. Other Plant Groups. Generic distinctions and those of higher To becategories give much less trouble than the lower ones. sure, there is some difference of opinion as to what categorical rating should be given to certain groups, e.g., whether they should be considered orders or families, families or tribes, genera or subIn fact, several families have been divided by certain genera. authorities who would call the legumes and the composites orders These differences are not disturbing, rather than families. however. Because of the absence of gradations in characters used in class, order, and family distinctions there is usually little atic units
difficulty in placing a plant correctly in these large groups, and even generic classification is seldom troublesome. More difficult is the problem of determining whether certain large groups, e.g., pteridophytes, dicotyledons, monocotyledons, umbellifers, and composites are monophyletic or polyphyletic. If they are polyphyletic, the logical procedure would be to divide them. Where a general term is needed for any collection of plants that may or may not have phylogenetic relationship and therefore may
or
may
not have a categorical rating, often having only a similar-
256
A TEXTBOOK OF SYSTEMATIC BOTANY
ity that does not indicate true relationship, the word 'group' is used. Thus, all deciduous trees form a group, or all aquatic
plants, or all insect-catching plants; but the word can also be applied to all roses, all mustards, or all grasses, members of which do show actual relationship.
The phylum
in zoology is a definite group consisting of related In botany the phylum is not generally recognized as a It is, however, a most valuable group, ranking regular category. The phylum is conusually between the class and the division. structed on logical phylogenetic lines. The division, on the other classes.
may be a heterogeneous polyphyletic collection. This criticism applies especially to the division Thallophyta, which is composed of bacteria, slime molds, and several unrelated classes hand,
of algae
and
fungi.
SUBSPECIFIC CATEGORIES In a general way the term 'subspecific categories those that are used to subdivide the species into groups.
More
definitely, the subspecies is
'
refers to all still
smaller
a category in
itself,
ranking between the species and those still lower. Most species are not thus subdivided, since the species is the unit of classifiThere cation, but a few exceptions are made by some botanists. are several kinds of subspecific categories. The variety is the subspecific category that is someVarieties. times used in the classification of wild plants. Linnaeus, the great exponent of binomial nomenclature, gave more than 200 varietal names in his 'Species Plantarum,' thus establishing trinomials. Varietal names can still be found in some botanical manuals, e.g., in Gray's 'New Manual of Botany,' seventh edition, and in Coulter and Nelson's 'New Manual of Botany.'
An example is Salix glaucops var. glabrescens Anders. Usually the varietal distinction is based on a single minor character such as epidermal hairs or size, the plant otherwise being like the Britton and Brown, in species of which it is called a variety. their 'Illustrated Flora of the Northern States and Canada,' entirely eliminated varietal names, since they are really a form of However, the desirability of retaining them in some cases cannot be denied.
trinomial nomenclature. If it
seems advisable, varietal names based on morphology or, once established, they can be eliminated
alone can be avoided,
PRINCIPLES OF TAXONOMY
257
two ways. The trivial character on which they are based can be ignored and only the generic name and the specific epithet used, or, if the character seems of sufficient importance, the varietal name can be raised to the rank of species. Thus Salix glaucops glabrescens can become simply S. glaucops or S. On the other hand, a specific epithet may be reduced glabrescens. A sand plum was named Prunus to the rank of a variety. Watsoni by Sargent and changed to Prunus angustifolia var. Watsoni by Waugh. Morphological observations alone, unsupported by experimental evidence, may be insufficient to determine whether a group should be rated as a species, a subspecies, or a Certainly these lower categories subspecies, varieties, variety. are not as definite categories as genera, species, races, forms, etc. and higher categories, and taxonomic authorities 1 differ in their in either of
usage.
There is at present considerable controversy as to whether the older term 'variety,' used by Linnaeus, Gray, and others, should be replaced by 'subspecies.' Some hold that the word 'variety' has so many different meanings that it should be used botany only for agricultural and horticultural productions. Others claim that it has served well in the past for subdivisions of wild species and that this usage should be continued. Varieties or species based on fine distinctions of a somewhat permanent character must not be confused with ecological or environmental modifications of a temporary nature. It is well in
known habitats
that closely related individuals growing in different may vary considerably, so much, indeed, that they are
sometimes called different species. It would be desirable, though sometimes impracticable, to have representatives of related Such tests have species grown side by side for comparison.
shown that some species are practically identical if grown in the same environment, and research along these lines could be used to eliminate many superfluous specific names from our manuals. There would also be involved, in some cases, the practice of including in the specific description qualifying statements concerning the effect of environment and corresponding records showing the
habitat of the specimen in question.
The work now being done in
1 See Robert T. Clausen, On the Use of the Terms 'Subspecies' and 'Variety,' Rhodora, 43: 157-167, 1941; also, F. Raymond Fosberg, Subspecies and Variety, Rhodora, 44: 153-156, 1942.
A TEXTBOOK OF SYSTEMATIC BOTANY
258
by ecologists will greatly strengthen our taxonomic For further discussion of this topic see page 261. systems. In most species of Horticultural and Agricultural Varieties. this field
cultivated plants, different varieties are recognized. Examples are the Delicious variety of apple, the Golden Bantam variety of sweet corn, the Marquis variety of wheat, and the Spencer
Generally these varietal distinctions are based on qualities of economic importance, such as size, color, or Such varieties are generally the products of the practical flavor. plant breeder, but occasionally they are found by man rather than variety of sweetpea.
produced by him. The present tendency of some botanists is to avoid the term for wild plants and restrict it to cultivated ones. Among some parasitic fungi, notably the Biological Races. rusts and smuts, it has been found that a species is made up of races that are morphologically alike but differ in their ability to attack different host plants. Puccinia graminis, for example, includes dozens of such races.
One
of these
can attack certain
and grasses, while others can attack different hosts and perhaps some of these as well. The races are distinguished from grains
each other through experiments carried out by inoculating with the spores of a strain of the fungus to be tested a large number of related hosts, differing in species or variety, and noting which ones are parasitized and which ones escape. Usually these biological races are
numbered but not named.
Serological Types of Bacteria. Pathogenic bacteria of certain species that cause human diseases have been divided into types on
the basis of their behavior toward the blood serum of persons or animals injected with the bacteria or their products. In effect the serum diagnosis is a comparison of the proteins of one species
with the proteins of other species, those with proteins most similar being interpreted as most closely related. It has long been known, and recent Ecological Modifications. studies have emphasized, that morphological differences may be a direct result of environmental conditions and are not heritable.
In some cases the mistake has been made of giving new varietal or These variants of a specific names to such plants. entitled to a not taxonomic nature are temporary rating. The term ' strain ' applies to a line of plants from a Strains.
even new
single source.
It is
under cultivation.
used for either higher or lower plants that are Thus each seed house or nursery may have
PRINCIPLES OF TAXONOMY
259
own strain of Golden Bantam corn or Golden Wax bean; anyone can catch a strain of Rhizopus nigricans from the air, and bacteriologists isolate strains of Bacillus subtilis from the soil. Strains of the same species or variety are not necessarily unlike each other quite frequently they are practically identical. its
CONTRIBUTIONS OF OTHER BRANCHES OF BOTANY TO TAXONOMY There is at the present time a considerable uniformity of opinion as to the relationships of the larger groups of plants, groups that we believe have been represented on the earth for
many
centuries.
There
every reason to suppose, however, that evolutionary In all likelihood some species are still going on. still giving rise to newer ones, although others are, for the present at least, remaining constant. Such a situation has always We do not expect new families characterized organic evolution. or orders to come into existence suddenly, but new species are is
processes are
inevitable.
It is natural, therefore, that research in this field
should be concentrated on species and subspecies. Keeping in mind the great goal of taxonomy in
its effort
to
plants and plant groups, past and present, along phylogenetic lines, and realizing the scarcity of records or direct evidence on which to base a complete phylogenetic system,
organize
all
systematists are using every branch of biology that offers any The most contributions to the solution of taxonomic problems. are of these plant paleobotany, geography, cytology, important genetics,
and ecology.
Some
of the
most
effective
work
is
done
through a combination of two or more of these branches of biological science.
Paleobotany and Plant Geography. Both of these subjects have been studied for a long time and have great interest in themselves.
Recently, use
origin, history,
is
being
made
and development
of
of plant
them
work out the from the standgroups to
point of plant relationships.
has been possible to determine the locality and geological period at which the group originated, information that suggests its probatye ancestors, and to trace its spread from the genera, original source and its branching into smaller groups Ecology here becomes a part of the picture in species, etc.
Often
it
A TEXTBOOK OF SYSTEMATIC BOTANY
260
determining and explaining the distribution of the species as they Much of modern research in taxonomy consists in studying limited groups, such as genera, from every angle, including historical development, and using the results obtained as the evolve.
basis for a taxonomic
monograph.
times plants practically identical in morphology but growing in different parts of the world have been given the same generic but different specific names, and some that have been
Many
given the same
name when found
have been found to be
in widely separated regions
different in their tolerance of ecological
when brought
together and therefore probably deserve This suggests that the physiology of a plant with respect to its adaptability to environment should be considered along with morphology in determining species. Cytology and Genetics. For many years cytology consisted merely of a study of the finer details of plant and animal strucIt has since been ture, with emphasis on those of the nucleus. enlarged to include an interpretation of the behavior of the organs conditions
different
names.
of the cell, especially in reproduction. Genetics makes use of the other branches of biology, especially of and findings cytology
Mendel's work, to establish laws and principles governing evoluthe fundamental basis of taxonomy. This subject has been ' Mechanism of Evolution' on page 19. briefly discussed under All evolutionary change appears to be based on the behavior of the chromosomes and their included genes. These in turn are known to be affected by environmental conditions, such as The effects are initiated while extreme temperatures and rays. tion
X
the nuclei are dividing or uniting and cause changes in the offThe best known of these results, which some would class spring. as abnormalities, are changes in the the chromosomes polyploidy, etc.
number and composition
of
and changes in the genes which is little themselves, about yet known. Indeed, many of the variations and mutations that have been observed in plants will require much work for their explanation. Cytology and genetics work together so closely that to carry on research in either field one should be well versed in both. These fields, with ecology, have become the strongest supplements to the older taxonomy based on comparative morphology and anatomy. Ecology. The subject of ecology is no longer restricted to observations on the effects of climatic and other environmental
PRINCIPLES OF TAXONOMY
261
conditions and noting the kinds of plants found associated with
each other, but in conjunction with cytology and genetics it is offering deeper explanations than were previously available into the meaning of taxonomic relationships.
A simple type of ecological experiment is now becoming more widely employed on taxonomic problems to supplement the morphological observations.
It consists of
studying representa-
tives of related groups, such as different races of the same subspecies, different subspecies of the same species, etc., when grown side by side in a uniform garden. The differences one observes in the wild state between related plants may be hereditary, or environmental, or, as is usually the case, a combination of both.
When the plants are assembled in a uniform garden these hereditary differences will stand out, unconfused with modifications caused by unlike environments. Another step is to study the same plants in different habitats. This may take the form of comparing the growth of individuals brought to regions differing strongly from each other in climate, or submitted to different local conditions in the same climate. The purpose of such experiments is to study the reactions of the individual and to compare the range of tolerance of related plants Here the ecological aspect of the to a given series of conditions. experiment merges with the genetic, because the range of tolerance
environments is genetically determined. Often perennials are employed that can be propagated vegetatively, so that parts of the same individual can be grown simultaneously under different conditions. In this way the heredity of the plants is the same, and the differences that develop between them will be due to modification by the environment only. of plants for different
Transplantation experiments have shown that the morphology of the plant, while controlled by both heredity and environment, is less affected, except for size, by the environment than many
What is more important, it has been learned that environmental conditions sort the natural units botanists have assumed.
presented to them, such as species, subspecies, populations, etc., with a ruthless hand, completely eliminating many and forcing For others into definite geographical patterns of distribution.
some species are narrowly limited in their distribution to the only environment to which they are suited, as the redwood, Sequoia spp., while others such as the yarrow, Achillea milliinstance,
A TEXTBOOK OF SYSTEMATIC BOTANY
262 foliurrij
are adapted to
many environments and have a wide
distri-
Species of wide distribution are furthermore found to be composed of many races, each adapted to a different climatic
bution.
These climatic region and usually distinguishable in appearance. races of widely distributed species are the basis of the experimentalist^ subspecies.
The Experimental Method
in Taxonomy. For centuries the was based on comparative morphology and anatomy alone, although it had been observed that the successful crossing of plants could be accomplished only between those that classification of plants
were closely related. Only during the present century has the significance of geographic distribution been generally appreciated. Through research work in genetics, cytology, ecology, and plant
geography a newer experimental method of studying taxonomic problems is being developed that should prove to be a valuable supplement to the older one. This method is being developed simultaneously in several centers, notably in Scandinavia under the stimulation of the work of the Swedish botanist, Gote Turesson, in Great Britain, and in the United States by the Carnegie Institution Stations.
of
Washington and the Agricultural Experiment is being done in zoology.
Related work
The
experimentalist attempts to assemble in his gardens as forms as possible of the group he is studying, using the hermany barium as a source of reference to the forms that may be looked Then he hybridizes these extensively. Some for in nature. crosses are failures, others are successful, producing fully fertile hybrids, while still others produce partially or completely sterile
hybrids.
Cytological studies show some of the nuclear changes, chromosome numbers. Gradually a picture of the
especially in
All degrees of genetic relationship of the forms is built up. in with closely are but forms the relationship general found, similar morphology, which the observer would presuppose to
belong to the same species, are found to be highly interfertile. Likewise, plants of unlike morphology ordinarily prove to be
However, expectations genetically unlike and incompatible. based on appearance do not always accurately forecast experimental results. From a consideration of the combined evidence offered by the morphology, distribution, genetics, cytology, ecology, and reactions to transplanting, the experimentalist is able to arrange
PRINCIPLES OF TAXONOMY
263
his plants in units of different orders of magnitude. On the basis of their genetic affinities he determines which groups are to be
treated as species, which as subspecies, etc.
and the
From
the herbarium
what names can best be applied Since the resulting classification is based upon facts, it will more closely approximate the aim of
literature he determines
to these units.
various kinds of
taxonomy
to present a true picture of phylogenetic relationships classification based upon only one or two kinds of
than would a facts.
The
units
first
worked out by such methods were given genetic-
Originally, no attempt was made ecologic terms by Turesson. to correlate these terms with existing taxonomic terminology; but as experimental evidence accumulates, it becomes possible to 1
compare the names
of natural units determined by experiment commonly employed in taxonomy. Since the two systems are based upon different characteristics, however, an
with those exact
statement
of equivalents is quite impossible.
The following terms, the first three of which were proposed by Turesson, are correctly applied only to groups whose rank has been determined by experiment. They are presented here because they are entering taxonomic literature to an increasing extent as the experimental methods are becoming more
widespread.
A
cenospecies is a group of plants that can be linked together by Considerable genetic incompatiat least slightly fertile hybrids.
and much morphological dissimilarity may exist among its members. One or more ecospecies are included in a cenospecies, which is frequently the equivalent of a taxonomic genus or
bility
subgenus.
An ecospecies is a group of plants whose members are interfcrtile among themselves but
are prevented from free intercrossing with
other groups by either complete or partial genetic barriers. When the ecospecies is morphologically distinguishable from others, it corresponds to the taxonomic species.
An
ecotype
is
a group of plants adapted to a particular environ-
ment but capable of producing fully fertile hybrids with other Its identity is ecotypes, if any exist, of the same ecospecies. maintained by ecological isolation operating with natural selec1
TURESSON, GOTE, The Genotypical Response
Habitat, Hereditas, 3: 211-350, 1922.
of the Plant Species to the
A TEXTBOOK OF SYSTEMATIC BOTANY
264
A morphologically distinguishable ecotype is equivalent to a subspecies or geographical race. A biotype is a population consisting of individuals with iden-
tion.
tical
genetic constitution.
It is
of
no recognized taxonomic
importance.
A
modification is a nonhereditary difference caused direct action of the environment in influencing growth. fication
by the
A
modi-
may be confused with hereditary differences such as mark
the biotype or even the ecotype and can only be distinguished from these by comparing the plants when grown in the same
environment.
Like biotypes, modifications have no taxonomic
standing. Since herbaria
and botanical manuals the world over use
generic and specific names based on morphology, it is not expected that these will be replaced soon by other names based on experi-
ment, but
it is
hoped that revision by the experimental method
will gradually correct the exist.
many
errors in nomenclature that
now
Certainly this newer work gives a deeper insight into the
mechanism
of evolution.
MAJOR AND MINOR CHARACTERS The higher plants are so complex and have so many different characters that the early botanists were greatly perplexed to know which features were important for taxonomic purposes and which unimportant. Naturally those of greatest importance would be used as a basis for main divisions and those of lesser importance for the subdivisions. They made the fundamental mistake of classifying the higher plants primarily into trees, shrubs, and herbs. Each of these was then subdivided into smaller groups.
The beginning student in systematic botany has a similar probHe wishes to know which characters should be family lem. which are the ones used for separating genus and and which are too trivial or too unreliable to have a taxo-
distinctions,
species, nomic value.
In modern taxonomy an effort is made to have the larger groups, e.g., classes, show the more ancient phylogenetic branchings and the smaller groups, e.g., genera and species, show the more recent branchings. The question then arises: Which mor-
and which indicate recent These points have now been fairly well established, and
phological characters indicate ancient origin?
PRINCIPLES OF TAXONOMY
265
the student of today can be guided to some extent by studying the classifications and the analytical keys in use and noting the characters used for distinctions
between
classes,
families,
genera,
species, etc.
In classifying the Spermatophyta we now recognize the covering of the ovules, number of cotyledons, and arrangement of the fibrovascular bundles as major characters used for making classes
and etc.
subclasses, while size and shape and surface coverings hairs, are minor characters used in making species. Inflores-
cences, arrangement of leaves
on the stem, and union
of floral
parts have an intermediate rating. Stability.
Almost without exception the more stable struc-
tures or characters, such as those listed above as major, are This means that results of ancient evolutionary departures.
groups that differ with respect to these structures have existed for a relatively long time. On the other hand, the unstable qualities, such as length of stem, fleshiness of root, hairiness, and color of petals, indicate more recent changes and may be quite variable. Vegetative versus Reproductive Structures. The older classifications were based mostly on vegetative parts, no especial attention being given to flowers and fruits. Linnaeus, about the middle of the eighteenth century, strongly emphasized the
advantages of using reproductive parts in classification. He used no vegetative characters for describing genera. The great French botanist, A. P. de Candolle, who lived a generation later, At the present time morphological followed the same plan. characters of all kinds are used, but the reproductive parts are most emphasized. Practically the only vegetative structures of
major importance for purposes
of
taxonomy
are those of the
fibrovascular system of steins and leaves. Carpels, stamens, petals, and receptacle are of almost equal rank with fibrovascular
structures
and because
of their greater variety
have a much wider
range of usefulness. Clear-cut versus Intergrading Characters. Those major characters that are used for dividing the spermatophytes into classes have long ago reached a state of equilibrium. They are
Intergrading conditions between flowering and flowerless plants and between the enclosed and the naked ovules can be imagined and may have existed at one time but apparently do not exist now. Likewise, the characters used for dividing the
now
clear-cut.
A TEXTBOOK OF SYSTEMATIC BOTANY
200 class
angiosperms
into
the
subclasses
monocotyledons
and
dicotyledons viz., number of cotyledons in the seed, distribution of vascular bundles in stems, and character of venation in the
show very few intergrading forms
at this time.
Minor
characters, however, are very likely to be intergrading.
There
leaves
be every degree of pubescence, of floral coloration, and of size and shape of leaves. Some gradations are clearly expressions of environment. It is likely that others express evolutionary branchings so recent that the types have not yet become fixed. They may be merely differences of degree and represent a
may
FIG. 94. Intergrading characters. Leaves from a single shrub of mountain maple showing different degrees in the extent to which the margins are cleft. Every gradation between any two of the leaves shown above can be found.
which certain individuals, strains, varieties, or have advanced farther than others in the same category. It is common taxonomic practice, based on experience and reason, to hold more closely to major than to minor characters. If a plant shows any departure whatever from a written description with regard to a major character, it is usually rejected at once from that group. If it fails to agree in an intermediate condition in
species
character, such as
identity
is
number
of petals or dehiscence of fruit, the
The plant may, however, differ, two minor characters; but the more of the more doubt is thrown upon the identity. It this connection that related species sometimes
strongly questioned.
in degree at least, in one or
these
it
may
be said in
violates,
hybridize in nature, thus increasing the difficulty of identification. Certain oaks and willows are examples.
PRINCIPLES OF TAXONOMY
267
Homologues versus Analogues.
Morphological comparisons mislead one unless he has a fundamental understanding of homologous and analogous parts. Structures similar in appear-
may
ance and function
same part analogous, tures
may
of the plant
may
likewise all
be homologous,
i.e.,
root, stem, or leaf
specialized from the or they may be only
All leaf strucspecialized from different parts. be regarded as homologous with each other, and stems and all roots, regardless of their degree of
i.e.,
Analogous structures. A, moss plant. B, white heather. The moss plant are parts of the gametophyte, while those of white heather are parts of the sporophyte. C, leaf of wandering Jew. D, cladoThe cladophyll, although leaf-like in appearance phyll of greenhouse smilax. and function, is a specialized stem, borne in the axil of a scale-like leaf. Although similar in appearance, analogous structures do not indicate relationships. FIG. 95.
leaf-like structures of the
specialization.
In the case of leaves, homology
may
apply to
parts rather than to entire leaves. Thus the thorns of the black locust are homologous with stipules, while thorns and tendrils of
other plants may be homologous with petioles or with stems. However, a leaf structure can be only analogous to stem or root structures, and stem structures may be analogous but not homologous to leaves or roots. The leaf-like cladophyll of common
analogous to the true leaf, as is also the so-called leaf of the moss, which is a part of the gametophyte generation. Analogous structures are similar in appearance, but
greenhouse smilax
is
A TEXTBOOK OF SYSTEMATIC HOT ANY
268
may
homologous structures
or
may
not resemble each other.
The cladophyll
just mentioned, the thorn of the hawthorn, and the tuber of the potato are all homologous with stems. It may be
stated as a general proposition that where the structures performing a given function in two plants are only analogous, these plants
For example, it is rare to find in the same genus one plant with tendrils .that are specialized stems and another with tendrils that are specialized leaves. The same may be said with regard to thorns. Likewise, large, colored, petallike bracts do not usually occur in the same genus with largeare not closely related.
petaled flowers.
Analogous structures are rather strong, then,
A
a
c
in
o
Fia. 96. Homologous structures. A, leaf of lilac. #, tendril of yellow C, thorn of barbeiry. D, stamen of lily. yetchling between two large stipules. A.11 are homologous structures, i.e., they have a similar origin arid are all potenA comparison of homologous structures is significant in detcrmintially leaves.
ng relationships.
No very general rule can be laid down, indicating differences. for homologous structures. They are so numerous and however, so varied that
they
may
indicate
any degree
of relationship.
Remarkable development in one direcSpecial Structures. tion characterizes certain plants, notably the devices for catching insects,
the floral structures of the orchids, and various xerophytic
These must be regarded as moderately strong adaptations. characters for purposes of classifying the plants possessing them, but they have a very limited application. Habitat. Many descriptions of specimens include the habitat. Phis has value as a suggestion but is treacherous as a character for classification, since the agencies for plant distribution may
from their usual haunts. Under these circumstances there may be considerable variation from the written description of the species, for environment determines in carry
some individuals
far
PRINCIPLES OF TAXONOMY some measure the
size,
269
breadth of leaves, succulence, hairiness,
etc.
Ease of Comparison. For generations botanists have fought a tendency to give undue importance to certain superficial characters that results in artificial groups. It may have been found convenient to call all the lower plants that have no chlorophyll, fungi; all plants below the liverworts, thallophytes, and all woody plants with staminate flowers in catkins, Amentiferae; but to regard any of these groups as phylogenetic units, in the light of present knowledge, is a monstrosity on a par with classing butterTendencies of this kind on a smaller flies and bats with birds. scale are numerous. Such artificial groups may be recognized under common names, such as fungi and seed plants, but we should, where possible, avoid such technical or scientific names as Hyphomycetes and Thallophyta. Hyphomycetes and Amentiferae are now practically obsolete terms, and Pteridophyta and
Thallophyta
may become
so.
One
of the greatest duties of the
systematic botanist is to perfect the natural system of classification and to present it in a form that will be scientifically correct and yet convenient enough to gain recognition in a world where efficiency is a valued attribute.
CHARACTERS OF SPERMATOPHYTA if we could say that one character for used class always distinctions, another for family distincWere plants perfectly for another generic distinctions, etc. tions, standardized in their morphology, this could be done; but they are
It
would be very convenient
is
not.
We must,
therefore,
make
the best of conditions as
we
find
however, to give the student some idea of the methods by which the different categories are distinguished that a discussion of the values and uses of the more
them.
It is so desirable,
prominent characters will be given. Probably all botanists agree that a phylogenetic arrangement of the flowering plants is like the trunk and branches of a tree. One conception of to remember
It is important illustrated in Fig. 92, page 238. in this connection that the same character ( e.g.,
it is
apetalous or unisexual flowers or united carpels) sometimes appeared later in one group or phylogenetic branch than in another, as a separate evolutionary act, and may therefore be used either as an ordinal, a family, or a generic distinction. Most
A TEXTBOOK OF SYSTEMATIC
270
BOTANY
all in interpreting the significance of different charthe fact that phylogenetic groups are based not on single characters but on combinations of characters. To divide the
important of acters
is
angiosperms into two subclasses, one consisting of all plants having simple leaves and the other of all plants having compound leaves, with no other characters in common, would be absurd and unquestionably artificial. Roots. When bulbs, tubers, rhizomes, etc., which are not properly parts of the root system, are excluded, underground Roots are hard to parts have but a limited taxonomic value. observe, and, having no division into nodes and internodes, they are relatively characterless. Also, they are much affected by the For these reasons many descriptions make character of the soil.
no mention
of roots,
and they are practically never used for though in some families, such as
specific or generic distinctions,
Cruciferae, taproots are the rule, while in others, such as Gramineae, the roots are mostly fascicled. Probably the most usable character of roots is their longevity. On this basis plants are divided into annuals, biennials, and
The strength of this character varies considerably, being mostly a family, a generic, or a specific distinction. Stems. In early times stems were very much used in classifying plants, and even today their importance is not minimized.
perennials.
One
of the
most dependable characters found in higher plants
is
the distribution of fibrovascular bundles. that,
if
spermatophytes
It is generally agreed are only considered, the arrangement in a
by the gymnosperms and the dicotyledons, the more primitive form, and the scattered arrangement in the monocotyledons is derived from it as a more recent departure, although we must concede the likelihood that remote fern-like cylinder, illustrated
is
ancestors of the
number
gymnosperms had scattered bundles also. The and buds at the nodes may be looked upon as a
of leaves
character of the stem rather than of the
leaf.
This character
is
of
intermediate value, being usually a family or generic distinction, but it is sometimes specific. Actually there are some plants the lower leaves of which are alternate and the upper leaves opposite.
The
degree of lignification and the longevity of the stem, distinguishing trees and shrubs from herbs, are now regarded as intermediate characters. Some families are wholly woody and a
very few wholly herbaceous, but most of them are mixed, having
PRINCIPLES OF TAXONOMY
271
The distinction is usually a generic one. Ancestrally, the woody stem is the older. Branching habit is a very weak character, often determined by both woody and herbaceous members.
environment and seldom used for categories larger than species. The trailing habit of vines is an intermediate character of generic or family importance.
The taxonomic value
of leaves is about on a par with Primitive leaves were probably simple rather than and had branched or netted veins. The venation is a
Leaves.
that of stems.
compound
character of major importance, being one of the distinguishing features between dicotyledons and monocotyledons. It should be mentioned, however, that a few of the monocotyledons, as
Smilax and Trillium, have netted-veined leaves, though the venation here is closed rather than open. The compounding of the leaf is an intermediate character. Usually it is a family or even an ordinal distinction, but sometimes it has only generic In the family Rosaceae, particularly, there is a lack of value. uniformity.
deciduous
is
The
fact that
some leaves
are persistent
often of value in classification.
and others
The evergreen
con-
having persistent leaves, is generally recognized as primitive, although it is probable that some evergreen angiosperms had deciduous ancestors. The character has usually a generic value as there are no large families of angiosperms entirely dition,
i.e.,
evergreen.
The form
of simple leaves is a weak character, generally used with others to distinguish species. along hairs are considerably used for specific distinctions, Epidermal but they have little value for the higher categories
Mention has been made of the strong modern to emphasize reproductive structures in taxonomy. No tendency doubt the solitary flower, probably typifying the strobilus or cone Inflorescences.
of the pteridophytes and gymnosperms, is more primitive than the collective inflorescence. Inflorescences have an intermediate
rating usually of generic value, although some families are uniform as to type. Some trouble is given here by intergrading characters, since racemes grade into spikes and both racemes and
A few inflorescences are complicated by spikes grade into heads. the fact that small flower clusters are so arranged that larger inflorescences are thus formed.
the Compositae
may
The heads
of certain
members
be single, as in the sunflower, or they
may
of
be
A TEXTBOOK OF SYSTEMATIC BOTANY
272
arranged in panicles, as in yarrow. In the Gramineae the spikelets may be arranged in panicles, as in oats, or in spikes, as in timothy. Flowers. In comparative morphology the flower is usually regarded as a specialized strobilus, in which the lower sporophylls have become sterilized to form sepals and petals arid the upper have changed into stamens and carpels. Unfortunately, fossil remains that show the details of transition are wanting. The axis of the strobilus is shortened to form the receptacle of the This strobiloid or hypogynous flower of the primitive type. occurs regularly in lower monocotyledons and lower dicotyledons. In the cotyloid or epigynous flower of the higher monocotyledons
and dicotyledons, the axis is actually depressed into a cup conThis is usually an ordinal or subclass taining the carpels. distinction, but in some of the transitional families there is lack of uniformity among genera. Aside from the flower axis the carpel is the most important organ taxonomically. It is the unit structure of the gynoecium.
The
primitive condition is that of many separate carpels, reduction in number and union to form a compound pistil being a later
development.
Basing our evidence on the
recent studies of the floral vascular anatomy,
fossil
record and on
we may
learn of the
probable origin of carpels and of their organization into the various ovary types. It is generally accepted that the primitive angiosperm carpel, as it existed in prehistoric ages, consisted of a modified leaf -like structure with ovules borne along the margins. These primitive carpels contained a midrib and two marginal veins extending upward from the base. The ovules were attached to the marginal
As ages passed, such a structure is believed to veins (Fig. 97a). have folded together with the ovules inside. The result was a simple ovary, having a single cavity and a parietal placenta (Fig. This is the simplest 976), i.e., one situated on the ovary wall. in is found members of and of the pea family, for today pistil type and In the about half of the rose buttercup family example. or there are four more, usually many, simple pistils on a family common receptacle, comprising the gynoecium of a single flower. A compound ovary represents the union of two or more simple ovaries.
but
it
It has, typically, as
may have
many placentae as there are carpels,
either one seed
chamber or more than
one.
In
PRINCIPLES OF TAXONOMY
273
tracing the evolution of the compound ovary it may be assumed that there was a gynoecium of separate carpels (three in this instance, as indicated in Fig. 97c), which united with their placentae toward the center. The result was a three-chambered
compound ovary having axial placentation and three seed chambers (Fig. 97d). From this type of compound ovary a second has been derived type by the withdrawal of the partitions and the floral axis ovule
parietal placenta ovule vein {marginal
midrib midrib a.
c. three
simple
wanes
primitive carpel
d.
compound ovary axial placentation
b.
simple ovary
e.
compound wary
parietal placentation
f.
compound ovary
fret central placentation
One conception of the evolution of the compound ovary from isolated FIG. 97. three in this case. The primitive ovaiy a, a flat leaf-like cladophyll hearing ovules on marginal veins, folds up to form a simple ovary h. In this case three such ovaries form c, but in others the number varies. By symphysis the simple ovaries become united with axial placentation d or with parietal placentation e. A further evolution of the axial placentation is the failure of the septa to develop, owing to reduction of the inner caipellary walls, giving If the central axis to which the ovules are attached free-central placentation/. in / is shortened, basal placentation results. (Drawings contributed by Miss Florence Mekeel of the Bailey Hortorium, Cornell University, and designed by G. H. M. Lawrence.) carpels
three placentae until the septa have disappeared and the placentae are situated on the inside of the ovary wall. The result
a three-carpellate compound ovary having one seed chamber and parietal placentation (Fig. 97e). A third type is also derived from the type having axial placentation and differs from it in the absence of the cross partitions, the ovules and their placentae remaining at the center on a central column (Fig. 97/). The
is
type is called free-central. An advanced evolutionary development over the free-central type of placentation
of
this
latter
A TEXTBOOK OF SYSTEMATIC BOTANY
274
placentation exists in the pigweed and buckwheat families, where reduction of the central column has left only a single ovule
borne at the base of the ovary. While a plausible explanation is given here for the evolutionary development of the types of compound ovary, it should be remembered that there are other means by which the same end may have been achieved; e.g., it is probable that in some plants the parietal type of placentation may have been evolved from the marginal union of several, open, primitive 1 carpels rather than as here outlined. Carpellate variations are, for the most part, major characters
used for ordinal and family distinctions, though in respect to certain details, such as number and length of styles, a lesser rating must be given them.
Stamens are of considerable importance in classifying plants. Decrease in numbers, union of filaments, and sterility of anthers are among the newer evolutionary developments. They have an intermediate rating, usually for family or generic distinctions.
The
point of insertion relative to the petals
importance.
is
of considerable
Absence of pistils or stamens, resulting in unisexual be looked upon either as degeneracy or as a form
flowers, may of specialization
whereby the likelihood
of close pollination is
family or a generic distinction. The perianth is usually regarded as part of the system of stroThe calyx bilate leaves that long ago ceased to produce spores.
reduced.
It is generally either a
rarely absent but presents so little variation that its taxonomic is limited, Color, other than green, is a derived quality. The corolla is much used in classification. It is relatively easy of
is
value
In primitive flowers observation, and it presents much variety. takes the form of many separate petals symmetrically arranged on the receptacle and each similar in appearance to the others in
it
the same flower.
Their union to form gamopetalous flowers must be given a variable rating. Whole orders show this character in the higher dicotyledons, but it has developed to a limited extent elsewhere in families otherwise polypetalous. Apetaly is a somewhat weaker character of family, generic, or even specific distinction. Irregularity of corolla is usually a family distinction but The color of petals is usually a weak character. be may generic. The orange and deep-yellow colors are quite dependable, but 1
This explanation was contributed by G. H. M. Lawrence of the Bailey Hortorium, Cornell University.
PRINCIPLES OF TAXONOMY
275
gradations from white through pale blue or purple to violet are
common and may be Pollen Grains.
misleading.
Taxonomists have been prone to overlook an
of morphological characters, those of the pollen Considerable research has been carried on in this field, has been shown that pollen characters are reasonably con-
important set grains.
and
it
Fio. 98. 2,
Morina
alpina.
6,
Pollen grains of different species of plants. I, Cobaea scandens Persica. 5, Circaec 4, Pa-ssiflora kermesina. 3, Cucurbita Pepo.
Cannabis saliva. 8, Pinus Pumilio. 9 7, Albuca minor (dry and moistened). 11, Dianthui 14, Salvia gluti13, Gentiana rhaetica. Corydalis lutea.
Convolvulus sepium.
Mimulus moschatus. carthuaianorum. 12, nosa. (After Kerner.)
10,
stant for each species and that related species generally have Keys to families have grains quite similar in certain respects.
been made based on pollen characters alone. 1 The chief characters of pollen grains are size, general shape, germinal apertures and surface markings, such as spines, ridges, and furrows. II will be noted that, while most morphological characters of highei plants are expressions of multicellular structures, those of poller ^See R. P. Wodehouse, 'Pollen Grains,' McGraw-Hill Book Company Inc., 1935.
A TEXTBOOK OF SYSTEMATIC BOTANY
276
These have long been grains are characters of the individual cell. used in classifying the lower plants, especially the fungi. In addition to the morphology of individual grains, the pollen masses
show considerable variation, in some being powdery and in others waxy or viscid. Pollen characters have family, generic, and specific value.
For purposes of analytical keys it is best Fruits and Seeds. not to depend too strongly on fruits and seeds, for much identification is done with immature plants. Indeed, it is often annoy-
Although ing to find fruit characters used in analytical keys. some of these characters, such as the numbers of seed chambers
and ovules, can be determined from the flower fruits,
other qualities such as
pistils or
size, color, fleshiness,
young and dehiscence
of fruits and size, shape, and markings of seeds develop later. These are for the most part rather weak characters, with the
exception of the method of dehiscence. More dependable characters are the number of cotyledons, the presence or absence of
endosperm, and the position and shape of the embryo. A special art has been developed recently in agricultural work that of identifying plants, particularly weeds, by seed characters alone. Skill in this field has considerable value in detecting In some cases seed impurities in seeds of cultivated plants. characters are sufficient to distinguish species; in others only generic identification is feasible. Starch Grains. Flowering plants
show almost endless variety
Even in in the size, shape, and structure of their starch grains. different species of the same genus clear-cut differences are often found.
They
are not
much used
in
taxonomy, but by means of
them
adulterations of starches and starchy products are often detected with the microscope. Their use for the identification of species has future possibilities. /.Morphological Indicators of Phytogeny .
To
facilitate piecing
together our morphological data into a phylogenetic system classification we need to know many details of the trend evolution.
there 1
is
Most
This knowledge has been derived slowly, but
of of
now
rather uniform agreement on the following principles: of these rules
were stated in
slightly different
1
form by Charles E.
Bessey, The Phylogenetic Taxonomy of Flowering Plants, Ann. Mo. Bot. A few others have been added by Alfred GunderGard., 2: 109-164, 1915. sen, Evolution in Flowering Plants, Brooklyn Bot. Oard. Leaflets, Ser. XI,
PRINCIPLES OF TAXONOMY
277
1. Plant relationships are up and down genetic lines, and these must constitute the framework of phylogenetic taxonomy. This will naturally form a branching but not a reticulate structure, except in the formation of species and varieties by hybridization.
2. Some evolutionary processes are progressive (upward) while others are regressive (downward, ' degenerative ') 3. Evolution does not necessarily involve all organs of the
plant at one time or in the same direction. One organ advancing while another is stationary or retrograding.
may be
Rice
Banana
Corn
Bean FIG. 99.
Wheat
Eight kinds of starch grains showing differences in appearance. 'Plant Life,' D. Van Nostrand Company, 1942.)
Oat (From
Evolution has generally been consistent, and when a particular progression or regression has set in, it has persisted for 4.
generation after generation. 5. In any natural group the chlorophyll -bearing plants precede the non-chlorophyll-bearing ones. 1 Saprophytes were derived from independent forms, and parasites usually from saprophytes among the lower plants and from independent forms
among
the flowering plants.
No. 9, 1923; and by J. Hutchinson, 'The Families of Flowering Plants,' pp. 6 and 7, Macmillan & Company, Ltd., 1926. 1 Exception should be made of the most ancient primitive life, which probably possessed no chlorophyll, since its production had not yet evolved. Many believe that the bacteria and the blue-green algae had a common ancestry lacking chlorophyll.
A TEXTBOOK OF SYSTEMATIC BOTANY
278
the seed plants the stem structure with collateral is more primitive than that with scattered bundles.
Among
6.
bundles arranged in a cylinder
Tracheids are more primitive than vessels (tracheae). Scalariform vessels are more primitive than vessels with
7. 8.
round
pits.
In most groups of seed plants woody members have preceded the herbaceous ones. 10. In most groups of seed plants erect members have preceded the vines. 11. Perennials are more primitive than biennials, and biennials 9.
are usually
more primitive than annuals.
were first persistent (evergreen) and However, evergreen angiosperms were probably derived from deciduous angiosperms. 13. The spiral arrangement of leaves on the stem preceded that of the opposite and whorled types. 14. Spirally imbricate floral parts are more primitive than those that are whorled and valvate. 15. In angiosperms simple leaves are more primitive than comHistorically, leaves
12.
later
deciduous.
J
leaves.
pound 16.
Among the seed plants the netted venation of leaves is more
primitive than the parallel venation. 17. Usually structures with many similar parts are more primitive, and those with fewer and dissimilar parts are more
advanced, i.e. a. The many-parted flower is the more primitive, the type with few parts being derived from it, and the change is accompanied by a progressive sterilization of sporophylls. :
1
This
is
the statement given
by Hutchinson.
Bessoy had earlier stated,
'Historically the arrangement of the leaves in pairs on the stem is held to have preceded the spiral arrangement in which the leaves are solitary at the
This is reasoned from the fact that in dicotyledonous plants the leaves (cotyledons) of the embryo are formed two at a node while in the monocotyledonous plants there is but one at a node. nodes.' first
As a matter of fact, many families in both monocotyledons and dicotyledons contain some species with one arrangement of the foliage leaves and other species with the other arrangement, sometimes both in the same genus. Also, some individual plants have one arrangement of the lower leaves and the other arrangement above. It is evident, therefore, that the change from either arrangement to the other is an easy one. For this reason the principle must be applied with discretion, although it has value in a study of floral organs.
PRINCIPLES OF TAXONOMY
A
b.
is
279
condition in which the perianth consists of like segments in which sepals and petals are unlike
more primitive than one
each other.
Regular flowers preceded irregular ones. Flowers with petals preceded apetalous ones, the latter being
c.
d.
derived by reduction.
Numerous carpels represent a more primitive condition than
e.
few
carpels.
The presence
of numerous stamens indicates a more primthan that of few stamens. g. Evolution in angiosperms is believed to have proceeded from seeds with two coats to those with only one. 18. Symphysis of parts is an advanced character, i.e. a. Polypetalous flowers are more primitive than gamopetalous ones, the latter being derived from the former by symphysis. b. Separate stamens preceded united stamens. c. Separate carpels represent a more primitive condition than /.
itive condition
:
united carpels. 19.
Hypogyny
is
the primitive condition and from
and epigyny have been derived. 20. In most cases at least, the
solitary flower is
it
perigyny
more primitive
than the inflorescence. 21. Bisexual flowers preceded unisexual flowers, which were derived from them by reduction. 22. The monoecious condition is earlier than the dioecious. 23.
Simple and aggregate
fruits
24.
The
contains
primitive
seed
embryo; the advanced type has food is stored in a large embryo 25.
A
straight
embryo
is
preceded multiple
little
fruits.
endosperm and a small or no endosperm, and the
instead.
usually more primitive than a curved
one. 26. The same evolutionary phenomena have often been repeated as separate occurrences at different times and in different This statement refers to loss of parts of the plant kingdom.
chlorophyll, loss of petals, stamens, and carpels, acquisition of fleshy texture in fruits and of various types of thorns, change from simple to compound leaves, from erect to prostrate habit,
and from hypogynous to perigynous or epigynous insertion of and lateral union (symphysis) of petals, stamens, and
floral parts,
carpels. 27. In determining the closeness of relationship
between two
280
A TEXTBOOK OF SYSTEMATIC BOTANY
it is usually best to compare with each other the more primitive, or basal, members of each group, rather than those that are most highly specialized or those that are
families or other groups
simplified by reduction. Some of these rules are statements of established facts, while others must be looked upon as general principles with probable
Most phylogenetic systems of taxonomy conform to exceptions. these principles, and they should serve as guides to every student in the analysis of such systems. In summarizing this discussion several points are to be emphasized: (1) that in defining the different groups of plants, combinations of characters must be considered; (2) that evolution has
caused certain characters such as unisexuality, irregularity of compounding of leaves, and saprophytism to appear repeatedly and independently in different groups; (3) that occasionally, perhaps by coincidence, similar combinations of charflowers,
acters appear in different groups, resulting in like individuals of different ancestry (polyphyleticism) ; (4) that there have been certain general tendencies in the evolution of the flower, notably
reduction in number, fusion, and specialization of parts; and (5)
that only approximate taxonomic values can be attached to most of the characters used for classification. /
In the Single Characters versus Combinations of Characters. beginnings of our present system of classification the tendency was to base a group of plants on a single character and to use this character to distinguish it from all other groups. Thus we had, as the primary groups of flowering plants, trees, shrubs, and herbs, Even as late as the regardless of floral and leaf characters.
eighteenth century Linnaeus prepared a system of classification based chiefly on single characters such as number of stamens
page 285). Gradually botanists came to realize that all, or at least many, characters must be taken into consideration jointly in determining what plants make up a class, family, genus, or other category. To get a full comprehension of this fact the student should turn to the descriptions of families given in Chap. VII and VIII. There he will discover, if he has not already done so, that there is scarcely any morphological character that all members without exception have in common, but the combinations of characters found bind the species into one family. (see
CHAPTER XI SYSTEMS OF TAXONOMY It is difficult to appreciate the strength and weakness of our modern systems of classification without a knowledge of the Students at first assume struggle by which they came into being. that botanists have reached perfection in classification and
nomenclature; then, as a sequel to disillusionment brought about by the discovery that there is some disagreement, they are prone to emphasize the failings and minimize the virtues unless they are made to realize the immensity of the problem and the handicaps under which the makers of systematic botany labored. Nomenclature Preceded Taxonomy. There can be no doubt
names to certain plants before they attempted The first were, of course, common names With the limited intercourse in many languages and tongues. that then prevailed among peoples and the entire lack of scientific work requiring exact terminology, these common names and No need was felt the loose application of them were sufficient. that people gave
to classify them.
for
a formal
classification.
PRE-EVOLUTIONARY SYSTEMS OF TAXONOMY the centuries prior to Darwin's 'Origin of Species' no one outstanding basis for classification. Up to the sixteenth century they drifted like a ship without a rudder, with classifications based on economic uses of plants
Through
all
(1859), botanists used
Then, gradually, morphology came into recognition as superior to other taxonomic criteria, not at first because it was known to indicate phylogenetic relationships, for these were not known to exist, but because it coincided most closely with a feeling or instinct for 'natural affinities.' Taxonomy Began with the Greeks. There are some who believe that the ancient civilizations of China and Egypt had predominating.
considerable advancement in systematic botany and the medicinal uses of plants, but if so their work had no influence
made
281
282
A TEXTBOOK OF SYSTEMATIC BOTANY
on these subjects as we know them. The foundations of systematic botany as we know it today were laid by the Greeks, notably Theophrastus and Dioscorides. Beginning several centuries before the Christian Era, the Greek physicians found in some plants actual medicinal properties not to be confused with superThe fame of this work spread to the Roman stitious beliefs. Empire and other parts of Europe and created a desire for what we would now call an international system of nomenclature and taxonomy. The grouping was at first largely an economic one, however, and the nomenclature became a heterogeneous mixture of Greek, Latin, and other names, varying with the country using it A few of the names still survive. Aristotle, and more particularly his pupil Theophrastus, made some attempt to extend botanical knowledge beyond the scope 1 of medicinal plants. Theophrastus has well been called the Father of Botany. Although his writings were made some 300 years before the birth of Christ, they were incomparably better than any others before the sixteenth century of the ChrisHe clearly recognized several hundred species and a tian Era. few families, although he had no system of categories such as are used today for classification. These Greek pioneers made the fundamental mistake of trying to make life processes the basis of classification; and the structures for carrying on these processes about which little was known were given a rating according to the importance of the physiological process. Nutrition was considered the most important; hence vegetative structures unspecialized roots, leaves, and stems were used for the main The writings of the Greeks embodied too few subdivisions. observations on what plants are and too much philosophizing as
how they might be expected
to
to be.
Taxonomic Development in Southern Europe. The work begun by the Greeks languished for a time and was then revived, culminating in the philosophy and classification of the Italian, He wrote a set of sixteen Cesalpini, in the sixteenth century. volumes on plants. The first was philosophical, making much of such minor distinctions as cultivated versus wild plants, trees versus shrubs versus herbs, and using curious mixtures of Theophrastus' 'Enquiry into Plants,' an English translation, shows an astonishing amount of botanical knowledge, along with some faulty 1
deductions.
SYSTEMS OF TAXONOMY
283
morphology and medicinal virtues. In the fifteen other volumes he divided the plant kingdom into fifteen heterogeneous groups including some animal forms. Cesalpini's work was remarkable in its attempt at that early date to classify the whole plant kingdom, and it made a profound impression on the botanists of southern Europe, but it lacked a consistent morphological basis and little of it has survived.
Taxonomic
Development in Central Europe. Systematic European states followed a course that was somewhat different from that developed in southern Europe. botany
The
in the central
botanists of this central region, particularly those of GerHolland, were striving, first, to find and identify the
many and
medicinal plants of the Greeks and to add to the number, and then to gain greater knowledge of plants in general. To this of the ancients, made extensive wrote exhaustive descriptions (sometimes with illustrations), established botanical gardens, and, finally, as a result of laborious comparisons, they began to make classifications. In their first attempts they did little abstract reasoning but
end they studied the writings collections,
followed rather closely morphological similarities and differences and like Theophrastus, showed quite accurate perceptions of ' ' natural groupings, even though they were not at that time ;
guided by a knowledge of evolution. The strength of their work lay in their numerous and closely comparative observations and in the predominance of morphological characters over economic Slow and ponderous thinkers, they did not quickly distinctions. formulate complete classifications; but certain groups such as Umbelliferae, Leguminosae, Gramineae, Labiatae, Malvaceae, of the Compositae became quite definite entities
and a part
oases, as it were, in the desert of unclassified plants, or crystals forming in an indefinite solution.
Some
incidental contributions to
taxonomy are worthy
of
note, especially the illustrated herbal of Brunfels (1530), the descriptive materia medica of Bock (Tragus, 1530), and the glossary of technical terms by Fuchs (1542), each work the first of It is evident its kind worthy of mention in botanical literature. that the Holland botanist, de Lobel, sensed quite keenly the natural relationships of plants; for in his work, written toward the end of the sixteenth century, he grouped many plants correctly,
though submitting no formal system
of classification.
A TEXTBOOK OF SYSTEMATIC BOTANY
284
His writings probably had much influence on the systems of de Jussieu and his contemporaries. Gaspard Bauhin, a Swiss botanist, climaxed forty years of arduous work in systematic botany with the publication of 'Pinax' in This publication 1623, in which he described some 6,000 species.
had the great merit of using generally the binomial system of nomenclature and has proved to be a valuable book in tracing synonyms. While Bauhin did not set forth the special value of the binomial
system or urge uniformity in its adoption, there doubt that his work stimulated Linnaeus to do so later. Fortunately, there appeared in this science, as in others, a few early European workers who had a clear insight into some of the principles involved, and who, step by step, worked out a plan of classification that we now accept for the most part as sound and reliable. By rejecting the errors and retaining the good points out by their predecessors and contemporaries they brought is little
important groups of the plant kingdom A few more significant men and their works will be mentioned, but most of them will have to be omitted. John Ray. The botanists of western Europe (England and France), following the morphological method to the exclusion of philosophy and economic usage, were active in organizing the fragmentary findings into definite systems. The English botanist, John Ray, in his 'Historia Plantarum,' completed in 1704, proposed a system, certain portions of which have survived to the present day: established
as
many
of the
we know them today.
I.
II.
Herbae a.
Imperfectae
b.
Perfeetae (flowering) Dicotyledones (with two cotyledons) Monocotyledones (with one or no cotyledon)
(flower-less)
Arbores a.
Monocotyledones
b.
Dicotyledones
These main groups were subdivided into thirty-three smaller ones, some of which corresponded fairly closely to our present families. Others were heterogeneous, including even animals.
The conspicuous error of Ray's system is faulty subordination in giving major value to the distinction between woody and herbaceous stems, as did the Greeks and Romans before him. Its lasting value lay in its distinction
between monocotyledons
SYSTEMS OF TAXONOMY
285
and dicotyledons, and to that extent
it became one of the great foundation stones of our present classification. Carolus Linnaeus. The greatest contributor to systematic
botany up to the middle of the eighteenth century was Linnaeus. A native of Sweden, he traveled throughout Europe visiting other botanists and making extensive comparisons of flora; and being a brilliant thinker, he was able to combine, with great powers of discrimination,
the work of
and contemmost thoroughly sorting the wheat from the his predecessors
poraries,
His
chaff.
contribu-
chief
tions were to nomenclature, those to taxonomy being
he never proposed a system of classification at all
indirect, for
satisfactory to himself or of He did, to be lasting value.
an artificial exclubased almost system on floral characters, the sively stamens being given a preponderance of attention; but publish
sure,
the
insertion
of
parts
hypogynous, perigynous, and epigynous tion also, ing value.
received recogni-
and
this had a lastLinnaeus realized
Carolus Linnaeus (1707Great Swedish naturalist. He described and named in any plants and animals, laid emphasis on floral structures, and did much to establish the FIG.
100.
1778).
binomial system.
the imperfections of this scheme and regarded it as a temporary makeshift until a more natural system could be devised. This
he began but did not live to complete. His artificial system had the effect, however, of focusing attention on the taxonomic value of floral structures and made a profound impression on the His 'Species Plantarum' (1753), describbotanists of his time. ing
all
species
known
at that time,
and
his
'
Genera Plantarum'
(5th ed, 1754), similarly describing the genera, stand today as the greatest of botanical classics. These works, with his successful promulgation of the binomial system used, but not established,
by Bauhin, and
name immortal.
his clear-cut conception of species
have made
his
A TEXTBOOK OF SYSTEMATIC BOTANY It is generally conceded that the French was the founder of the present system of de Jussieu, botanist, he took freely from the work of his predecestaxonomy, though While familiar with Cesalpini's work, he made but limited sors.
A. L. de Jussietu
He
divided the plant kingdom into fifteen classes, them seed plants. These in turn were divided into orders, some of which were roughly comparable to our families. His main subdivisions, as published in 1789, are as follows: use of
it.
fourteen of
I.
II.
ACOTYLEDONES.
Plants without cotyledons: Fungi, Ferns, Algae, Naiades (CLASS I) MONOCOTYLEDONES. Plants with one cotyledon
Mosses,
Stamens hypogynous (CLASS II) Stamens perigyiious (CLASS III) 3. Stamens epigynous (CLASS IV) DICOTYLEDONES. Plants with two cotyledons Stamens epigynous (CLASS V) Stamens perigynous (CLASS VI) 1. Apetalae Stamens hypogynous (CLASS VII) 1.
2.
III.
2.
Corolla hypogynous (CLASS VIII) Monopetalae Corolla perigynous (CLASS IX) Corolla epigynous (Anthers connate (CLASS
X)
Anthers free (CLASS XI) Stamens (CLASS XII) epigynous f Polypetalae -(Stamens hypogynous (('LASS XIII) (Stamens perigynous (CLASS XIV) Diclines irregulares, male and female flowers on different plants, corolla generally absent (('LASS XV) I
3.
4.
It will
be seen that de Jussieu abandoned the primary division
woody versus herbaceous stems, gave major consideration to the cotyledons, and made prominent use of petals and stamens. His system lacks modern conceptions in characters of vascular into
bundles, floral axes, petals, and carpels, but it has served as a basis on which by addition and correction the best systems have
been built. A. P. de Candolle. De Jussieu's system of classification was extended and improved by A. P. de Candolle (1819), a Frenchman who carried on most of his work in Switzerland. He was unquestionably the greatest botanist of his time and not only improved plant classification but set forth some important principles of taxonomy. To de Jussieu's recognition of the number of cotyledons, character or absence of corolla, and position of stamens
SYSTEMS OF TAXONOMY
287
de Candolle added, as a major character, the arrangement of fibrovascular bundles.
He
also
made some
progress in
the
classification of the lower plants.
Stephen Endlicher.
This distinguished systematist, working
in Austria, published a pretentious work on plant classification, which was completed in 1840. He followed de Candolle's system
to a into
extent but sub-
large
divided
the
more
kingdom and orders
plant
classes
(equivalent to our families). effort to group
He made an
plants above the thallophytes on the bases of apical growth,
growth in diameter, or both. This distinction led him to combine gymnosperms with dicotyledons, an error that was later copied by Bentham and Hooker. Morphological Discoveries. this time several impor-
About
tant morphological discoveries
were made that became serviceable in the classification of
plants
N ot able among these
were Robert Brown's studies on seeds, including the nature of the endosperm and the lack of carpellate coverings for the ovules in the gymnosperms;
FIG.
101.
(1778-1841).
-Augustin P. de Camlolle Great early botanist of
France and Switzerland. He contributed much to the rules of nomenclature and gave the world a system of plant classification that was an extension of the one proposed by Jussieu. (Courtesy of Alfred Gunderaen, Brooklyn Botanic Garden.)
Endlicher's anatomical stud-
showing the manner of growth in stems and distinctions between stem and root; Lindley's investigations of the vascular bundles in stems and leaves; and Hofmeister's embryological
ies,
studies, revealing among other things the alternation of generations. Hofmeister evidently realized that the alternation of
generations established a natural connection between the Bryophyta, Pteridophyta, and Spermatophyta even though Darwin's ' ' Origin of Species had not yet been published. Fortified
by these morphological
discoveries
and by a knowl-
288
A TEXTBOOK OF SYSTEMATIC BOTANY
edge of evolution, the later taxonomists were able to make very marked improvements.
EVOLUTIONARY SYSTEMS OF TAXONOMY In the midst of steady progress on the improvement of systems were purely and blindly morphological, the conceptions of species and other categories and the ideals of classification were profoundly modified by the introduction of the of classification that
doctrine of evolution.
Charles Darwin.
Probably the most epoch-making event
in
the entire history of biological science was the discovery of the That Darwin was not the first to get an principle of evolution. inkling of this principle seems to have been the
is
well
first
to
known, but with Wallace he comprehend its sweeping sig-
After the first wave of nificance ('Origin of Species,' 1859). excitement was over, systematists quite generally accepted the doctrine and began to revise their systems to fit the new principle of phylogenetic relationships. Fortunately, much that had already been done was usable, for all but the morphological systems had been pretty much eliminated from botanical taxonomy, and morphology has proved the best single criterion of
phylogeny.
Bentham and Hooker. These two great English systematists, contemporaries of Darwin, worked out in far greater detail than any of their predecessors a system of classification of the Spermatophyta that for some thirty years dominated the botanical world and has been modified rather than revolutionized to make the systems in use today. It is virtually an extension of the work of de Jussieu and de Candolle. In their ' Genera Plantarum' (1862-1883) they made a rather complete series of categories giving dicotyledons,
gymno-
sperms, and monocotyledons equal rank, equivalent to classes, with the gymnosperms between the other two, for they had not sensed the value of Robert Brown's discovery that gymno-
The dicotyledons were divided into three subclasses, the further sequence of categories being series, The cohort was practically cohort, order, genus, and species.
sperms have naked ovules.
equivalent to our order and the order to our family. There were altogether 200 orders (families) beginning with Ranunculaceae
and ending with Gramineae, Compositae being near the middle
SYSTEMS OF TAXONOMY
289
(No. 88). Probably most systematic botanists of today will agree that this system of Bentham and Hooker should have been perpetuated and amplified rather than replaced by the system of Engler. Julius von Sachs.
Until nearly the close of the nineteenth progress had been made with the classification of century the Thallophyta. Following the improvement of the microscope little
to a point of practical usability, Sachs in 1882 proposed a classification of these lower plants nearly on a par with that of Bentham and Hooker for the spermatophytes, though not so detailed.
THALLOPHYTES Containing chlorophyll

Class
Cyanophyceae Palmellaceae
(in part)
Not containing chlorophyll
Protophyta Schizomycetes Saccharomycetes Class II. Zygosporeae Conjugating cells motile I.
Pandorineae
Myxoraycet^
(Hydrodictyeae)
Conjugating cells stationary Zygomycetes Conjugatae (including Diatonmceae) Class III. Oosporeae Sphaeroplea fSaprolegnieae Vaucheria (Coeloblastae) I Peronosporeae Volvocineae
Oedogonieae Fucoideae Class IV.
Coleochaeteae Florideae
Characeae
The shrewdness
Carposporeae Ascomycetes (including lichens) Aecidiomycetes (Uredineae) Basidiomycetes
of this great Austrian botanist is
shown by
this phylogenetic classification in which he attempted to bring out the relationships of the different groups of algae to cor-
responding groups of fungi. While the classification contains some serious mistakes due to the inherent difficulty of the subject and the limited amount of detailed work that had been done on the Thallophyta at that time, the main concept
many A.
is
accepted by
botanists.
W.
Eichler.
Basing his work on a considerable study of
morphology, made in the light of the doctrine of evolution, Eichler (1883) made a classification of the entire plant kingdom.
A TEXTBOOK OF SYSTEMATIC BOTANY
290 A.
CRYPTOGAMAE I.
Division I.
II.
II.
Thallophyta CLASS: Algae (5 groups) CLASS: Fungi (3 groups, including lichens)
Division I.
II.
Bryophyta GROUP: Hepaticae GROUP: Musci
III. Division I.
II.
III.
B.
:
:
Pteridophyta CLASS: Equisetineae CLASS: Lycopodineae CLASS: Filicineae :
PHANEROGAMAE I.
II.
Division:
Gymnospermae
Division: Angiospermae I.
II.
Eichler's
CLASS' Monocotylcae (7 orders) CLASS: Dicotyleae I. SUBCLASS: Choripetalae (21 orders beginning with Amentaceae) II. SUBCLASS. Sympetalae (9 orders)
work covered the
entire plant
more of
kingdom and arranged plants somewhat
lower
the
definitely
de Jussieu.
cation
than did that His classifi-
was contemporary with Bentham and Hooker
that of
but much treatment
less detailed in
tho
the
of
flowering It corrected the error
plants. of placing the
gymnosperms
between the monocotyledons and the dicotyledons, but
unfortunately
it
placed
' Amentogether under the
taceae' the catkin-producing trees, including poplars, wal-
nuts, birches,
were FIG. 1930)*
102
Adoiph Englcr (1844Tho most influential taxonomist of his time and author of the great system of classification most extensively used today (Courtesy of Alfred Gundersen, Garden.)
Brooklyn
Botanic
and oaks, which
considered
primitive
because
of
flowers.
Other characters,
such as the
their
apetalous
pistillate flowers,
the fruits, and the structure of the wood, throw much doubt
SYSTEMS OF TAXONOMY on the closeness
of relationship
291
between the members of
this
group.
Engler and Prantl. of
Nearly half a century ago the
an extensive work by two German
first
volumes and
botanists, Engler
were published (1887-1 909).} This treatise, Prantl, ['Die nattirlichen Pflanzenfamilien,' covers the entire plant kingdom.
named did much of the work on the flowering plants many sections throughout the plant kingdom were assigned to other specialists. The Engler and Prantl system is a develop-
{While the authors
ment
and follows it in many respects. Its by the publication of Engler and Gilg's ' 'Syllabus der Pflanzenf amilien (10th ed., 1924), and both are expressions of what is commonly known as the Englerian system. of that of Eichler
usefulness
is
increased
In this system the seed-bearing plants (Spermatophyta) are designated as Embryophyta siphonogama and are further subdivided as follows:
EMBRYOPHYTA SIPHONOGAMA I.
Subdivision: 1.
2.
3. 4. 5. 6. 7.
IT.
Gymnospermae
CLASS: CLASS: CLASS: CLASS: CLASS: CLASS: CLASS:
Cycadofilicales
Cycadales Bennettitales
Ginkgoales Coniferae Cordaitales
Gnetales
Subdivision: Angiospermac 1.
2.
CLASS: Monocotyledonae (11 orders) CLASS: Dicotyledonae SUBCLASS: Archichlamideae (Choripetalac and Apetalae) (30 orders)
SUBCLASS: Metachlamydeae (Sympetalae)
The numerous
(11 orders)
orders are further subdivided into suborders,
families, and genera. In this system the woody plants with unisexual, apetalous flowers borne in aments (willows, walnuts, birches, oaks, etc., often called Amentiferae) are treated as among the most primi-
tive dicotyledons.
It will
be noted that the arrangement of
kingdom follows that of Eichler and is considered erroneous by many botanists of today. The work this part of the plant
has been recently revised, but the new edition still groups some of the distantly related amentiferous trees together and
A TEXTBOOK OF SYSTEMATIC BOTANY
292
It should be understood that assigns them a primitive position. the Engler and Prantl system did not base its phylogenetic con' ceptions on the morphological indicators of phylogenyY^iven on
pages 276 to 280 of this textbook, most of which are American conceptions. jv/To base a taxonomic system on these conceptions is to change or reject some important parts of the Englerian system. /The value of this work, considered as a whole, lies in its broad treatment of the entire plant kingdom, illustrations,
its
and
excellent
its
phylo-
genetic arrangement of
many
Being prepared by many authors,( it is not surprising that it lacks somegroups.
what ment.
in uniformity of treatAlso in some groups,
especially
among
the
lower
plants, phylogeny has been sacrificed for the convenience
obtained by artificial groupThis system now domi-
ing. FIG. 103.- -Charles E. Bessey (1845His life work at the University 1915). of Nebraska profoundly influenced the trend of botany in the United States. He was author of the first important
nates the
botany,
eld of systematic though not to the fi
exclusion of
all
others.
Charles E. Bessey. For American textbook of general botany the most part, American and founder of a great phylogenetic
system of plant tesy of
Raymond
collection
and
classification.
(Cour-
J. Pool.)
identification
systematic
botanists
havo
given their attention to the of
plants, of
herbarium making, and the writing
naming new species, manuals to cover the
vegetation of different parts of the country. With one notable exception they have not made extensive contributions to the
development of taxonomic systems, this work having been done This exception was Charles E. Bessey, chiefly by Europeans. who received a part of his training under Asa Gray. A great teacher and investigator, he did his last and best work at the University of Nebraska. Tn 1894, he submitted a system of classification that was a
SYSTEMS OF TAXONOMY
293
Bentham and Hooker, separating the gymnosperms from the angiosperms and reorganizing and rearranging a few orders of the latter. modification of that of
Bessey gave much attention to the problem of determining the morphological indications of primitive versus advanced conditions in vegetative and reproductive structures and proposed ' many of the morphological indicators of relationships' set forth in Chap. of this book. His final 1 work was published in outline form shortly after his death 2 in 1915.J It carried the classification only to the families, of which there were 300, subdivision into genera not being carried out. A condensation of it is as
X
^
follows: .
PHYLUM ANTHOPHYTA.
Flowering Plants
Subclass ALTERNIFOLIAE-STROBILQIDEAE
Order ALISMATALES Alismataceae and 8 other families Order LILIALES Liliaceae
and 12 other families
Order ARALES Araceae and 2 other families Order PALM ALES Pahnaceae only Order GRAMINALES Poaceae arid 4 other families Subclass ALTERNIFOl T^K-r.OTYLOIl)ffJV K Order HYDRALES r
Vallisneriaceae only
Order
I RID ALES
Iridaceae and 10 other families
ORCHIDALES Orchidaceae and
1 other family /Order CLASS OPPOSITIFOLIAE (DICOTYLEDONEAE)
Subclass QpPOSITIFOLIAE-STROBILQIDEAEi
Order RANALES Ranunculaeeae and 23 other families Order MALVALES
Malvaceae and 11 other families 1
BESSEY, CHARLES
E The ,
Phylogenetic
Taxonomy
of
Flowering Plants,
Ann. Mo. Bot. Gard., 2: 108-164, 1915. 2 The main skeleton of the Bessey system was published much earlier (Bot. Gaz., 24: 145-178, 1897) but was revised from time to time with respect to certain details.
294
A TEXTBOOK OF SYSTEMATIC BOTANY Order SARR ACE NI ALES Sarraceniaceae and
1
other family
Order GERANIALES Geraniaceae and 21 other families Order GUTTIPERALES Violaceae and 19 other families
Order RHOEDALES Brassicaceae and 6 other families
Order CARYOPHYLLALES Salicaceae and 16 other families
Order EBENALES Ebenaceae and 4 other families Order ERICALES Ericaceae and 5 other families
Order PKIMULALES Primulaceae and 4 other families^ * Order GENTIANALES Gentianaceae and 5 other families Order POLYMONIALES Solanaceae and 5 other families Order SCBOPHULARIALES Scrophulariaceae and 9 other families
Order LAMIALES Lamiaceae and 3 other families Subclass QpPOSlTIFOLIAE-CQTyT.rfT ^p. AJg
Order ROSALES Rosaceae and 22 other families Order MYRTALES Oenotheraceae and 14 other families Order LOASALES Cucurbitaceae and 4 other families Order CACTALES Cactaceae only Order CELASTRALES Vitaceae and 23 other families Order SAPINDALES Juglandaceae and 14 other families Order UMBELLALES Apiaceae and 2 other families Order RUBIALES Rubiaceae and 4 other families Order CAMPANULALES
Campanulaceae and 3 other
families
Order ASTERALES Reliant haceae and 13 other families
For some families Bessey used names different from those under which they are commonly known; e.g., Poaceae for Gramineae,
SYSTEMS OF TAXONOMY
295
FIQ. 104. Bessey's conception of the relationships of the orders of angiosperms. Relationship is indicated by position. The areas are approximately (Redrawn after Besaey.) proportional to the number of species in the orders. -
He also Brassicaceae for Cruciferae, and Lamiaceae for Labiatae. some families into smaller families to a greater extent than is
split
commonly done with 14 families.
e.g.,
making Composite an order
(Asterales)
A TEXTBOOK OF SYSTEMATIC BOTANY
296
of the orders to show phylogenetic relationWhile in his publication he listed the give in Fig. 104. monocotyledons before the dicotyledons, it must not be inferred
arrangement
ships
is
that this
is
to indicate that they are the
definitely stated
and shows
more primitive,
for he
in Fig. 104 his belief that the dicoty-
first ancL-ihat the monocotyledons branched from themjtt a very early^stage of their development. J
ledons appeared
off
COMPARISON OF THE SYSTEMS OF ENGLER AND BESSEY 'Since the taxonomic systems of Engler and Bessey show the greatest divergence of any of those that have received the support
prominent botanists of recent years, and yet both have great merit, it seems well to summarize their difference^ Origin. The two series of progressively improving taxonomic systems leading to those of Engler and of Bessey are given below of
:
John Ray (168&-1704) Jussieu (1789)
John Ray (1686-1704) Jussieu (1789)
Candoile (1819) Endlicher (1836-1840)
Candolle (1819)
Eichler (1883)
Bentham and Hooker (1862-1883)
Engler (1887-1909)
Bessey (1915)
Fundamental Conceptions.
Engler built his system of classiharmony with his ideas of phymost respects, correct; but many logeny, which American taxonomists and some in other countries feel that the fication of the
angiosperms in probably was, in
' dicta of Bessey (see 'Morphological Indicators of Phylogeny, page 276) are for the most part correct, and that his system built largely on them is a more natural one. It is pretty generally agreed that flowers have been evolved strobili of pteridophytes, but we have no complete set of
from the
forms either among living plants or among fossils. suggestive fossils are those of the extinct order of gymnosperms, the Bennettitales, which had reproductive strucWe can tures somewhat like the flowers of our angiosperms. transitional
The most
therefore only speculate on the steps evolved.
The two systems have many things some very important differences. ,
by which
in
flowers have
common, but
there are
1. Engler considered the monocotyledons primitive and the dicotyledons derived from them, while Bessey held that the reverse was true.
SYSTEMS OF TAXONOMY
297
Engler gave greater significance than Bessey to the union of petals (sympetaly), while Bessey gave greater significance to the 2.
epigyny versus hypogyny. generally conceded that flowers evolved from the
floral axis, 3.
It is
gymnosperms. Engler's conception was that the was unisexual, producing either microspores or megaspores but not both, and that its morphological equivalent is the ament, each scale of the strobilus having become a unisexual,
strobili
of
ancestral strobilus
Engler
j
Conception
Two cone-options of the evolution of the flower from the strobilus. FIG. 105. In the center is a strobilus. According to Engler this contained only megaspores or microspores, and the entire strobilus developed into an ament, pistillate or staminate, each flower being apetalous and derived from a sporophyll of the ament. According to Bessey the strobilus contained megaspores below and microspores above and developed into a single flower, the lower sporophylls becoming sterilized and forming sepals and petals, those next above forming stamens, and the upper ones forming carpels. The axis shortened and became the strobiloid receptacle. v
apetalous flower from which bisexual flowers and petaled flowers were later evolved. Bessey's conception is that the ancestral strobilus
was bisexual with both microspores and megaspores,
morphological equivalent is a single bisexual flower a buttercup. In the process of change the lower scales of the strobilus ceased to produce spores and became sepals and petals, those just above them evolved into stamens, and the upper ones evolved into carpels. Meanwhile, the axis of the strobilus to
and that
its
like
which the scales were attached shortened to form the receptacle. If it shortened only to a condition in which the top was convex or
A TEXTBOOK OF SYSTEMATIC BOTANY
298
the receptacle was 'strobiloid,' and the flower was hypogyIf it was depressed still farther so that the top of the receptacle was conqaye, the receptacle was 'cotyloid,^' and the
flat,
nous.
It was natural, therefore, flower was perigynous or epigynous. that Bessey should have given a higher value to the distinction between hypogyny and epigyny than did Engler, who had no such
explanation for these differences in the floral axis. 4. Bessey further considered the apetalous flower as an advanced type in which the petals had been lost by reduction and called attention to their presence as vestigial scales in some apetalous flowers, whereas Engler treated apetalous flowers as primitive and ancestral to flowers with petals. )
The 'Die
In 1905, Hans HalHer took issue with Hallier System. ' natiirlichen Pflanzenf amilien (1) in giving a different :
members of the angiosperms, (2) in regarding the 'Amentaceae' as primitive types, and (3) in the derivation origin to different
of the monocotyledons. system correcting these
He
proposed tentatively a phylogenetic In condensed form it is as
faults.
follows: A.
SPOROPHYTES I II.
II.
B.
Filicalcs
Lycopodiales a. Isosporae 6. Heterosporae Equisetales
SPERMATOPHYTES a.
Gymnosperms
(excluding Gnctaccac).
Cycadaceae. 2. Bermettitaceae. 3. Coniferae b. Angiosperms (A) Dicotyledons Polycarpicae (Magnolincac, etc.) Ranales (Nymphaeaceae, Rammculaceae, etc.) Rhoeadales (Capparidaceae, Cruciferae, etc.) 1.
I.
II.
III.
IV. Piperales (Piperaceae, etc.) V. Malvales (Malvaceae, Urticaceae, etc.) VI. Ebenales (Convolvulaceae, etc.) VII. Geraniales (Geraniaceae, etc.) VIII. Myrtiflorae (Myrtaceae, etc.) IX. Resales (Rosaceae, Leguminosae, etc.) X. Ericales (Ericaceae, Primulaceae, etc.)
XI. Sarraceniales (Sanraceniaceae, etc.) XII. Santalales (Santalaceae, Gnetaceae, etc.) XIII. Umbelliflorae (Cornaceae, Umbelliferae, etc.)
SYSTEMS OF TAXONOMY
299
XIV. Amentiflorae
XV.
(Salicaceae, Juglandaceao, etc.) Passiflorales (Onagraceae, Campanulaceae, Compositae, etc.) Centrospermae (Portulacaceae, Polygonaceae, etc )
XVI. XVII. Caprifoliales (Caprifoliaceae, etc.) XVIII. Tubiflorae (Labiatae, Solanaceae, etc.) (B) Monocotyledons (descendants
XIX. Helobiae
of
Nymphaeaceae)
(Alismaceae, Juncaginaceae)
(The work on the monocotyledons unfinished) It will be noted that the Hallier system was developed simultaneously with that of Bessey and has many features in common with
it.
The Work
In 1901, Richard Wettstein pub'Handbuch der systematischen In the third edition (1924) a book of 1,000 pages of Wettstein.
lished the first edition of his
Botanik.' covers the entire plant kingdom. The dicotyledons are regarded as polyphyletic and placed before the monocotyledons. Also, the lilies are considered more primitive than the grasses, which is a departure from the Engler and Prantl system. Wettstein considered the apetalous, amentiferous, woody plants to be more primitive than the Ranales (Magnoliaceae, Ranunculaceae, etc.) because fossils of the former have been found in older strata. It is
agreed, however, that
we have no
fossil
representatives of the
most primitive flowering
plants, so that paleontological evidence as to the antiquity of different groups of this class is not very conclusive.
The fourth edition, completed in 1935 after Wettstein's death, make any radical change in the system. The Hutchinson System. A more recent effort in this field is 'The Families of Flowering Plants,' by J. Hutchinson of the Royal Botanic Gardens, Kew, England; the first volume, on the
does not
dicotyledons, appeared in 1926; the second, on monocotyledons, in 1934. In its underlying principles it is much more like the
Besseyan system than the Englerian system, but it differs conIts main features are as follows: siderably from both. 1. It renews the ancient emphasis on the distinction between arborescent and herbaceous habit, but this character is here used As a result of giving major in conjunction with other qualities. two primitive or basal orders are emphasis to this distinction, recognized, the Magnoliales, mostly woody and giving rise to other orders that are mostly woody, and the Ranales, mostly
300
.1
TEXTBOOK OF SYSTEMATIC BOTANY
herbaceous and giving rise to other orders that are mostly herbaceous 2. Partly as a result of the distinction just mentioned in the first feature, certain groups containing both woody and her-
baceous members are made to appear polyphyletic, i.e., some members arising from one ancestry and others from a different
Such a position is given to the 'Apetalae,' the Urticales, the Umbelliflorae, and the Asterales, for example. Plants with apetalous flowers of course have no status as a phylogenetic one.
group, but the status of the others is debatable. Whenever it can be established that different members of a group have separate ancestry, the group should be divided and the parts given distinct names, if the interests of phylogenetic taxonomy are to be served
Otherwise, a reticulate arrangement is formed. 3. In the monocotyledons the floral axis is given less significance than Bessey would give it, thus rearranging the genera of
and Amaryllidaceae. the whole, the arrangement follows that of Bentham and Hooker. Even though some may doubt the wisdom of
Liliaceae
On
maintaining his distinctions between the various types of woody and herbaceous plants, all will agree that the system shows an advanced step in phylogenetic conception. Summarizing the work of the last half-century, we find two different tendencies: (1) the work of Eichler and Engler, placing monocotyledons before dicotyledons, deriving dicotyledons from gymnosperms with unisexual strobili, and giving Amentiferae a primitive position among dicotyledons; (2) the work of Bessey, Hallier, Hutchinson, and Mez, giving monocotyledons an early derivation from the dicotyledons, deriving dicotyledons from
gymnosperms with bisexual
strobili, regarding Amentiferae as a heterogeneous group simplified by reduction, and making Ranales, in the older sense of the term, the basal group of the dicotyledons.
The
botanists of this group, while agreeing on these large issues, hold different views on the relationships of various orders and
families and,
it
on very many
should be added, are quite in harmony with Engler points.

COMPETITION OF SYSTEMS It is regrettable that the systematic botanists of today are not in complete accord on taxonomic usage. All the systems in use at
SYSTEMS OF TAXONOMY
301
the present time agree in many particulars but differ in others. of them cover the entire plant kingdom, while others deal
Some
only with limited groups, such as the bacteria, the fungi, or the higher plants. Reasons for Lack of Accord. There are at least five reasons for existing differences in taxonomic usage. 1. Often phylogenetic relationships are difficult to determine, the existing evidences being very meager. Under these circum-
stances the superficial mind may reach a very definite conclusion on evidence that is far from proof, the keen progressive mind may tentatively accept the evidence and make use of it until new
evidence it
at
all.
is
found, while the slow or conservative mind will not use lines of evidence may point to one
Then, again, certain
relationship while other lines point to another. circumstances the progressives may be divided into 2.
Even though
Under these two groups.
the evidences conclusively establish certain may not be used because
relationships, the resulting classification
there is an artificial grouping that is more convenient. Let us suppose, for example, that the Zygomycetes, the Oomycetes, the Ascomycetes, and the Basidiomycetes were known to have origi-
nated at different times from as
and that the exact
many
different groups of algae, were established. Even under no doubt that some botanists would
lines of descent
these circumstances there
is
treat the algae as one group, implying relationship, and the Or, again, even though some of the newer confungi as another. ceptions such as those of Bessey, Hallier, Hutchinson, and Mez
still
are admittedly more in harmony with the evidences of phylogeny than are the older ones of Engler, the Engler and Prantl system
would nevertheless continue
in general use because of its accessibecause of a desire for uniformity in practice, or because it is easier to continue it than to change. It is indeed a criticism of some taxonomic specialists that they are content to use artificial groupings for plants rather than let bility,
phylogenetic consideration disturb their complacency. 3. Some confusion exists with regard to the names that should be applied to certain well-recognized groups. For example, among the family names we have Gramineae versus Poaceae,
Leguminosae versus Papilionaceae versus Fabaceae, Cruciferae versus Brassicaceae, Umbelliferae versus Ammiaceae, and ComSome of these are strict synonyms; positae versus Carduaceae.
A TEXTBOOK OF SYSTEMATIC BOTANY
302 others vary
somewhat
in their generic inclusions.
There are two
principles (sometimes conflicting) that determine which synonym should be used. One is that a name of almost universal accept-
ance should not be replaced by an obscure one. The other is that the first valid name used for a group should not be replaced by another. Because some follow one of these principles and others follow the other, we have inevitable disagreement. 4. Since categories are not hard and fast entities, but only manmade devices for dealing with plants collectively, it is natural that some systematists would give a higher rating than others to certain groups. Some authorities consider Pomaceae and Drupaceae as families; others, as tribes of Rosaceae. Numerous other examples could be cited, and this is, in fact, one of the greatest
forms of disagreement. 5. When a botanist has committed himself to a system of classification to the point of publishing it, he is likely to become unreceptive to evidence that would overthrow or greatly alter it. Criticism only makes him defend his ground more stubbornly, and he loses his attitude of open-mindedness. He and his opponents forthwith lead opposing schools of thought. For the sake of expediency a teacher may be forced to give his students a system of classification that he does not consider the best from the standpoint of phylogeny, because the available manuals and the general practice of the region make such a policy
necessary to avoid hopeless confusion. It is thus probable that the Engler and Prantl system is followed by many who, though appreciating
its virtues, also
recognize
some
of its faults
and
see
them. ways of Herbaria. Taxonomic classification expresses Organization The herbaria itself not only in publications but in herbaria. found in most universities and some other institutions, such as the of correcting
U.S. Department of Agriculture, are very large, some containing hundreds of thousands of specimens. These must be arranged in orderly fashion for convenience in the use of the herbarium. Most of them, the world over, are arranged according to the
Englerian system.
PRESENT STATUS OF ANGIOSPERM CLASSIFICATION It
must not be supposed that the
phylogeny
last
word has been said on the on since the
of the angiosperms, for researches carried
SYSTEMS OF TAXONOMY
303
time of Engler and Bessey indicate, as would naturally be expected, that neither one was able to picture natural classifiall parts of his taxonomic system, and improvements must be expected for years to come. The Englerian system is being used in most manuals of botany because of the detailed presentation it has been given in Engler and PrantFs ' Die natiirlichen Pflanzenfamilien,' a work of twenty-three largo volumes with many illustrations, in contrast with Bessey's system, which was published in brief outline form, carrying the
cation correctly in
classification
only to the family.
Many
botanists,
however,
especially those in America, agree with Bessey (1) that the dicotyledons are more primitive than the monocotyledons; (2) that the
dicotyledons are a natural, monophyletic group; (3) that the Ranales are primitive while the Amentiferae are neither a primitive
nor a natural homogeneous group; and
(4)
that apetalous
flowers are not to be regarded as primitive because they failed to evolve petals but were derived from flowers with petals that have
been
lost
through regressive development. for Revision. Differences of opinion concerning phylogenetic arrangement are natural and inevitable in the present state of our knowledge, and a shifting of ground must be expected
Need
It would be absurd for a as long as new evidence is forthcoming. botanical congress to seek to establish the facts by passing resoFacts cannot be lutions in favor of one system or another.
altered ever,
by proclamation. The writers of way by adopting
can well lead the
general treatises, howthe newer conceptions
whenever they appear to be well established. Present Tendencies. We have reached a stage where the most progressive systematists are content with nothing short of phylogenetic arrangements for all groups of plants, although some feel that so complete an accomplishment can never be realized. Any other plan is looked upon as artificial and temporary, or merely an unscientific convenience an expedient for some special purpose.
In certain parts of the plant kingdom the relationships are fairly Some excellent work has already been published revising the detailed arrangement of some of the small well understood.
groups certain families, genera, etc. The phylogeny of each group needs to be studied not only for its own sake but in the hope of getting more light on the relationships of some of the other perplexing groups.
A TEXTBOOK OF SYSTEMATIC BOTANY
304
Researches in the Taxonomic Field. The general adoption of the Englerian system in books and in herbaria has helped to stabilize taxonomic classification, but modifications and improve-
ments must be expected
in those groups
where the work has been
To
the very extensive studies that have been made for centuries in the field of gross morphology new lines of evidence are
faulty.
now being added. (2) (3)
The most fruitful
comparative anatomy, ecology and plant geography,
physiology, including
of these are (1) paleobotany,
especially of the fibrovascular systems,
'
(4)
genetics,
serum diagnosis.'
and
(5)
plant
CHAPTER
XII
THE LITERATURE OF SYSTEMATIC BOTANY Publications dealing directly or indirectly with the systematic, aspect of botanical science have always held a conspicuous place in botanical literature; indeed, a mere list of titles would consume hundreds of pages. To keep the size of this chapter down to
proper proportions relative to the rest of the book, the student will be given here but a few representative examples of different phases of the subject, especially since much of the literature is hardly within the grasp of the beginner but belongs in an advanced course. The following table of contents of this chapter will aid in finding any book that is cited here: Page 305 306
Media for Taxonomic Publication The Pearly Classics Fundamental Principles Morphological Fundamental Principles Genetic, Etc
307 309 312 314 316 319 322 324 326 327 329
Rules of Botanical Nomenclature
World Floras and Taxonomic Systems Regional Floras and Manuals Taxonomic Treatment of Limited Groups Cultivated and Economic Plants Nontechnical Floras
Paleobotany Indexes, Catalogues, Etc
Miscellaneous
MEDIA FOR TAXONOMIC PUBLICATION The
works were written before the invention and took the form of manuscripts, often Some of the most important of these have
earliest botanical
of the printing press bound in book form.
since been copied either as facsimile impressions or with or without translation.
by
printing,
In recent years taxonomic publication has taken varied forms research articles, monographs, general treatises, manuals, etc. As for American journals, the Bulletin of the Torrey Botanical Club
was formerly given over quite largely to taxonomic work, but 305
in
A TEXTBOOK OF SYSTEMATIC BOTANY
306
recent years it has become more general. Those that are now devoted especially to this field are American Midland Naturalist, Rhodora, Annals of the Missouri Botanical Garden, Journal of the Arnold Arboretum, Brittonia, Phytologia, Madrono, Darwiniana, Lloa. Lloydia, American Fern Journal, and Castanea.
From of
the standpoint of establishing priority in the publication descriptions of groups, all botanical works jour-
names and
in regular circulation are given equal nals, books, bulletins, etc. recognition, and, indeed, priority can be established through works not strictly botanical, although their use is unfortunate,
since articles they contain most interested in them.
may To
easily be overlooked
by those
discourage the publication of descriptions of species and other groups in obscure places, and especially in languages that are little used, recent rules have prescribed that a Latin diagnosis establish priority of publication.
must be given
in order to
THE EARLY CLASSICS In the older literature a few works stand out as remarkable productions for the period in which they were written. Most of these have profoundly influenced the development of the science. Enquiry into Plants. Written by Theophrastus in nine books.
Translated into English by Sir Arthur Hort in 1916; Loeb ClassiPublished in two cal Library, Harvard University Press. volumes with the Greek text and the English translation on opposite pages, giving a total of 908 pages. the most important of the botanical writings of Theothe oldest botanical work of value existing today. and phrastus real botanical information mixed with specumuch It contains and lative philosophy expresses freely the beliefs of the times, although in many cases the author casts doubt upon the super-
This
is
stitious ideas that
De Re
Rustica.
he records. Written by Marcus Porcius Cato more than a
century before Christ and printed in 1494; Loeb Classical Library, Harvard University Press, 1934. The book is devoted largely to agricultural
practices, methods of propagation, but plants are quite generally designated of these names are still in use. Said to be
and horticultural
culture, varieties, etc.,
binomially, and many the oldest botanical work written in Latin.
THE LITERATURE OF SYSTEMATIC BOTANY
307
Prodromus Systematis Naturalis Regni-Vegetabilis. By A. P. de Candolle, University of Geneva, and others. Seventeen volumes and four index volumes, 1824-1873; published by G. Masson, Paris. This extensive work, by far the greatest treatise of its day on systematic botany, attempted to describe all known plants and arrange them according to the natural system of de Candolle. 1 After the death of this great botanist in 1841, the work was continued for more than 30 years by his associates. Genera Plantarum. By Carolus Linnaeus, Upsala University. Fifth edition, 1754, 500 pages, unillustrated. This edition is official in establishing the limit of priority for generic names. It describes 1,105 genera of plants of for the
name
in
most
cases.
all kinds, citing the authority In general, the generic descriptions
of the seed-bearing plants are restricted to the flower, fruit,
and
seed, ignoring vegetative portions.
Species Plantarum.
By
Carolus Linnaeus, Upsala University.
First edition, 1753, two volumes, 1,200 pages, unillustrated; In this, the most used of the facsimile edition, W. Junk, Berlin. early botanical classics, Linnaeus assembled under their genera
up to that time, using very largely the binomial system but indicating varieties in some cases. Generic descriptions were not included. The work was partly the practically all the species described
A few the were but overlooked, previously published descriptions u in a landmark nomenclatural such was Plantarum' Species development that it was adopted as a starting point for priority in botanical names. result of his
own
observations and partly compilation.
FUNDAMENTAL PRINCIPLES MORPHOLOGICAL The
orderly taxonomic
work
ciples that are the results of
of today is based on many prinmuch painstaking research. Some of
known so long that their origin is obscure; others represent bold advances taken in recent times. The older works deal mostly with gross morphology and organization into catethese have been
newer ones with the and plant geography. ecology, gories, the
findings of cytology, genetics,
The Phylogenetic Taxonomy of Flowering E. Bessey, University of Nebraska, Ann. 1
'Th<5orie Elemental
de
la
Botanique,' 1st
Plants.
Mo. ed.,
By
Charles
Bot. Gard., 2, 1915, 1813; 2d ed., 1918.
A TEXTBOOK OF SYSTEMATIC
308
BOTANY
155 pages, illustrated by one figure showing graphically the He sets author's ideas of the relationships of the angiosperms. forth
many
principles of
taxonomy and from these constructs a
phylogenetic system of classification of the angiosperms.
His
and system have steadily gained favor, although they have been found open to improvement. This represents the only attempt of an American botanist to construct a system of classification, and it is very meritorious. principles
By
Descriptive Systematic Botany.
A. S. Hitchcock, U.S.
1925, 216 pages, An excellent reference Sons, Inc. book on many topics relating to collecting, identifying, and the The different codes of nomenscientific arrangement of plants. unillustrated;
clature that
First
of Agriculture.
Department
John Wiley
edition,
&
had been proposed up
to that date are presented in
comparison. The Generic Concept in the Classification of Flowering Plants. By B. L. Robinson, Harvard University, Science, 23: 81-92, 1906. The author here sets forth ideas regarding the correct delineation of genera and seeks to discourage the making of new genera on insufficient grounds.
Aspects of the Species Question. By C. E. Bessey, N. L. Britton, J. C. Arthur, D. T. MacDougal, F. E. Clements, and H. C. Cowles, Amer. Nat., 42: 218-281, 1908. A symposium giving a masterful presentation of the best American ideas on the species concept and especially on the Later concepts species or subspecies.
The Concept
of the
Genus. J.
A
problem of finely divided have since been proposed.
symposium by Harley Harris Earl Edward Sherff 67 Club, 349-389, 1940. The
M. Greenman,
Edgar Anderson, and W. H. Camp, Bui Torrey Bot. subject is presented by experienced taxonomists from several Bartlett,
,
:
viewpoints, but that of the experimental approach of geneticists ecologists receives only passing mention. Mass Collection. By Edgar Anderson, Ralph 0. Erickson,
and
and Norman O.
Ann. Mo.
Bot. Gard., 28: 287-374, 1941. research purposes samples that for papers explains of significant parts taken from a considerable number of individuals of a plant population in a given locality, representing a
This series
Fassett,
of
species, subspecies, variety, or race, have great advantages over Methods are given for single specimens taken in the usual way.
sampling, preserving, and using such mass collections.
THE LITERATURE OF SYSTEMATIC BOTANY Origin of Species. sixth edition, 1893.
309
By Charles Darwin. First edition, 1859; Two volumes, 305 and 339 pages, respec-
bound together
unillustrated D. Appleton-Century ComYork. This book, preceded by the brief pany, Inc., expositions of Wallace and Darwin on the same subject a year earlier, constitutes the first adequate presentation of the theory of the evolutionary origin of living things. It is written in the style of a research publication, referring to previous statements by tively;
;
New
It is the others, submitting evidences, and drawing conclusions. forerunner of a long series of works on evolution by Darwin and numerous other writers.
Evolution by
Means
of Hybridization.
edition, 1916, 166 pages
and 2
By J.
illustrations;
P. Lotsy.
First
Martinus Mjhoff,
A discussion well adapted to student use. The author dwells especially on the part played by conjugation in the formation of new species and varieties and thus paves the way for ' the The Hague.
the
modern
genetic
and
ecological conceptions,
i.e.,
experi-
mental method' of taxonomy. What Evolution Is. By George H. Parker, Harvard UniverFirst edition, 1926, 173 pages and 4 pages of illustrations; sity.
Harvard University Press. A highly authoritative, dispassionate presentation of the history, evidences, and mechanism of evolution as it has been disclosed by more than half a century of investigation
by many careful
and general
workers.
The book is
suited to students
readers.
Evolution for John Doe. By Ward Henshaw. First edition, The 1925, 354 pages, illustrated; The Bobbs-Merrill Company. from and here the all has studied a subject angles author, layman, presents a good, readable account of it that will appeal to other
laymen.
By Nathan
Fasten, Oregon State 456 1929, pages, and 75 illustrations; College. Alfred A. Knopf, New York. This book gives, in readable form, a well-rounded account of the development of our ideas concerning organic evolution, with emphasis on the evidences bearing on the subject and the laws governing its operation.
Origin through Evolution. First edition,
FUNDAMENTAL PRINCIPLES GENETIC,
ETC*
Por centuries plants were classified on the basis of their morphology and anatomy, and certain principles were evolved to
A TEXTBOOK OF SYSTEMATIC BOTANY
310
guide taxonomists in the interpretation of their observations. More references to these principles are cited above.
Some
have genetics, ecology, etc. based on both observation and experSome of these are reviewed below.
recently other branches of botany
added new iment.
lines of evidence
Principles of Genetics. By Edmund W. Sinnott and L. C. Dunn, Columbia University. Third edition, 1939, 408 pages and This book 147 illustrations; McGraw-Hill Book Company, Inc. serves admirably to give the genetic evidence concerning the methods by which evolution takes place in plants and animals. The New Systematics. Edited by Julian Huxley, England. First edition, 1940, 583 pages, illustrated;
The Clarendon
Press,
Twenty-two chapters, each written by a different author, who had specialized in the field covered and represented different nationalities. The book covers in a thorough and authoritative way the newer researches in ecology, plant geography, paleontology, genetics, and other fields that have a bearing on taxonomy and where possible correlates them with the older morphological findings and conclusions. It is the fullest exposition up to 1940 on the experimental method in Oxford,
England.
taxonomy. Genetics and the Origin of Species. By Theodosius DobzhanColumbia University. Second edition, 1941, 446 pages, Although written by a illustrated; Columbia University Press.
sky,
zoologist, this
book contains much
illustrative material
from the
plant kingdom. The fundamental principles brought out in explanation of the mechanism of evolution are applicable to both
animals and plants and represent the author's interpretation of the genetic researches in this
field.
The Genotypical Response
By Gote
Turesson,
of the Plant Species to the Habitat. Institute of Genetics, Askarp, Sweden,
The work was based on made from one environment of central and largely transplants northern Europe to another. Studies were made on the anatomy, cytology, and gross morphology of the transplants and on the results of hybridization. Here are introduced the terms cenospecies, ecospecies, ecotypes, and ecophenes as categorical equivalents of genera, species, subspecies, and variants but in a different way, the latter being based on morphology and the former on genetic and ecological experiments. Hereditas, 3: 211-350, 1922, illustrated.
THE LITERATURE OF SYSTEMATIC BOTANY
311
The Concept of Species Based on Experiment. By Jens Clausen, David D. Keck, and Wm. M. Hiesey, Amer. Jour. Bot., 26: 103-106, 1939. A concise presentation of the newer concept and other lower categories. In contrast with the older
of species
conceptions based on gross morphology, this newer conception is based on experimental work in which closely related plants are crossed and the resulting offspring (if any are produced) are studied under different environmental conditions, some plants being isolated and others given a chance to interbreed. Stability
under experimental conditions determines
in the product
category
its
species, subspecies, etc.
Experimental Studies on the Nature of Species.
By
Jens
Clausen, David D. Keck, and William M. Hiesey, Carnegie Institution of Washington at Stanford University, Publication
No. 520, 1940. Part I, on 'The Effect of Varied Environments on Western North American Plants,' has 452 pages, illustrated. Continuing the work begun by the late Dr. Harvey Monroe Hall of the same institution, the authors have transplanted a con-
number of species of perennials into three dissimilar regions to test the effects on them of the wide range of ecological conditions altitude, moisture, temperature, etc. found in siderable
California.
Some mention
is
made
of
chromosome numbers and
other cytological data, but the work deals mostly with ecology in relation to taxonomy, the cytological and genetic aspects being treated in a companion volume now in preparation. The Role of Isolating Mechanisms in the Differentiation of
Plant Species. By G. Ledyard Stebbins, Jr. Biological Symposia, 6: 217-233, 1942. This is representative of the recent papers reporting the results of researches undertaken to show the necessity of isolation for the prevention of cross-fertilization,
if
species
and other lower categories are to become established following hybridization.
kinds of isolating a valuable bibliography on
It also discusses the different
mechanisms and
their origin.
It has
the subject.
Chromosome Number and the Relationship of Species in the Genus Viola. By Jens Clausen, Ann. Bot. [London], 41 677-714, 1927. Based on original investigations and on citations from other cytologists, the chromosome numbers of more than forty :
Fourteen different numbers, ranging species of Viola are given. from six to thirty-six, are given. In a phylogenetic study the
A TEXTBOOK OF SYSTEMATIC BOTANY
312
number,
and shape
size,
of the
chromosomes are compared with
the morphological characters. Through crossing it was found that individuals sufficiently identical in morphology to be classed
Some species can be derived from unlike parentage. in and the offered for are partial complete sterility explanations as the
same
offspring.
RULES OF BOTANICAL NOMENCLATURE After Linnaeus had convinced the biological world that the
binomial system of nomenclature was the best one to use, the of plants was extensively carried on by many botanists were who widely separated and working independently, and much confusion resulted. To secure greater uniformity in procedure the leading botanists of the world have held a number of inter-
naming
national congresses and adopted rules of procedure. The rules that they adopted and that survived the action of later congresses are given below. Botanical nomenclature has become so compli-
cated that a
summary
of the
most important
rules
is
given on
pages 234 to 236 of this book.
Nomenclature and Botanical Congresses. By HerA brief review of bert C. Hanson, Amer. BoL, 31 114-120, 1925. the national and international botanical congresses up to 1910, with references to the publications of their proceedings, and codes
Codes
of
:
of botanical nomenclature.
Laws
of Botanical
Nomenclature.
By
Alphonse P. de Can-
dolle, translated from the French by Dr. Weddell, Amer. Jour. This paper gives the so-called Paris Code Sci., 96: 63-77, 1868.
in full, with editorial remarks.
International Rules of Botanical Nomenclature.
By John
Bri-
quet, Reporter General for the International Botanical Congress of Vienna, 1905, and Brussels, 1910. Second edition, 1912,
Gustav Fischer, Jena. Written in three languages, French, English, and German, in one volume. The English section covers 19 pages and the entire work 110 pages, of which 29 are devoted to nomina conservanda in Latin, applicable to the unillustrated,
three sections.
American Code of Botanical Nomenclature. By the American Nomenclature Commission, Bui. Torrey Bot. Club., 34: 167-178, 1907, unillustrated.
A
brief
statement of the reasons for advo-
THE LITERATURE OF SYSTEMATIC BOTANY
313
eating the American Code as a substitute for the recently formulated International Rules, followed by the rules themselves.
Type-basis Code of Botanical Nomenclature. By A. S. Hitchcock, U.S. Department of Agriculture, Science, 49 333The author, as chairman of a com330, 1919, unillustrated. mittee of the Botanical Society of America on generic types, here :
makes a brief report for the committee and records the rules recommended for adoption and known as the Type-basis Code. International Rules of Botanical Nomenclature. By John Briquet and A. B. Rendle of the Committee for Nomenclature for the 1930 Botanical Congress of Cambridge, 1935, Gustav Fischer, Jena. Written in three languages, English, French, and German, in one volume. The English section covers 26 pages exclusive of the nomina conservanda, etc. (20 pages). This work consists of
an amplification of
earlier rules.
and introduces the term 'epithet'
when
It includes the
for the
name
type concept of the species
stands alone without the generic name. It is the most code of International Rules of Nomenclature nearly complete thus far published, lacking only the amendments authorized at it
the 1935 Congress of Amsterdam. Additions and Amendments to the International Rules of
Botanical Nomenclature, Edition 3. By twelve botanists, Kew Roy. Bot. Gard. Bui Misc. Inform., No. 21932, pages 65-92. This is virtually a supplement to the International Rules as adopted by the 1930 International Congress at Cambridge. It embodies the work of the 1935 Congress at Amsterdam and the recommendations of committees authorized
minor changes
congress.
It consists of
and decisions concerning
groups that were controversial. Conservation of Later Generic Homonyms. By Alfred Rehder al.j Kew Roy. Bot. Gard. Bui. Misc. Inform., Nos. 6-9, 1935,
the
et
names
by that
in the rules, corrections,
of certain
pages 341-557. The subject matter is indicated in the title. Additional Nomina Generica Conservanda (Pteridophyta and Phanerogamae). By T. A. Sprague, Kew Roy. Bot. Gard. Bui. Misc. Inform. No. 3, 1940, pages 81-134. indicated in the title.
The
subject matter
is
Principal Decisions Concerning Nomenclature Adopted by the Sixth Botanical Congress at Amsterdam. By T. A. Sprague, This paper gives some of the most Jour. Bot. [London], 74, 1936.
A TEXTBOOK OF SYSTEMATIC BOTANY
314
important work of the Amsterdam Congress in simpler form than the
two publications
cited above.
Terminology of Types. By Donald Leslie Frizzell, Ainer. Midland Nat., 14: 637-668, 1933. This paper gives a brief discussion of nomenclatural types of plants and animals, followed by an extensive list of the terms, both those in current use and others that are synonyms or obsolete, for the different kinds of types, with definitions. It has a good bibliography of previous papers on the subject. Types of Species in Botanical Taxonomy. By W. T. Swingle,
A
discussion of the significance Science, 37: 864-867, 1913. of type specimens, the value and care of such specimens, and the methods of reproducing, or duplicating for distribution to It gives a brief classipractically the same as that It contains references botanists at the present time.
other herbaria, the one real type specimen. fication of
followed
type materials, which
by
to other papers on the
same
is
subject.
WORLD FLORAS AND TAXONOMIC SYSTEMS
A
few great taxonomists have had the vision to construct systems of classification for great groups of plants, such as the Spermatophyta. Some of these have been published in skeleton form for the higher categories only; others have been carried down to the species. All but one of these taxonomic systems have been the products of European botanists. That of Charles E. Bessey is the work of an American and is based partly on the earlier pub-
Europeans. All the systems now in use have had an evolutionary history and are not the product of any single lications of
botanist.
%
Genera Plantarum.
G.
Bentham and
D. Hooker, Kew, First three edition, 1862-1883, volumes, 3,577 pages, England. This monuunillustrated; published by Reeve & Co., London. mental work gives a fairly complete classification of the higher plants with a definite system of categories and descriptions of all
By
J.
The sequence is dicotyledons, gymnosperms, and monocotyledons. This work dominated the field of systematic botany more than any other prior to ' Die nattirlichen Pflanzenfamilien,' of Engler and Prantl. It used a system of categories somewhat
groups.
different
from that
of
today
cohort for order and order for
THE LITERATURE OF SYSTEMATIC BOTANY
Many consider the sequence of families to be natural than that of Engler and Prantl.
family.
315
more
Die natttrlichen Pflanzenfamilien. By Adolph Engler, Berlin, and K. Prantl, Breslau. First edition, 1887-1909, second edition in preparation, eight volumes of which have been published to The largest work of its kind ever written, filling twentydate. three volumes and occupying several feet of shelf space. ProThis great work fusely illustrated; W. Engelmann, Leipzig. covers the entire plant kingdom and is world-wide in its scope. It carries the classification to genera and in some cases to species, but there its
is
considerable lack of uniformity in treatment owing to many botanists having taken part in the
composite authorship,
This publication has dominated the systematic botany since its publication. Most herbaria of the world and most botanical manuals follow its sequence of
preparation of the treatise. field of
families.
There
away from some
is,
however, at present a considerable breaking
of its phylogenetic conceptions.
By Adolph Engler and Ludwig Eleventh edition, 1936, 419 pages and 476 illustrations; Gebriider Borntrager, Berlin. This book is usually thought of as a condensation of 'Die natlirlichen ' It consists of an introduction on principles Pflanzenfamilien. of classification, a list of families and higher categories according to the Engler system, and a brief discussion of families and Syllabus der Pflanzenfamilien.
Diele, University of Berlin.
.
tribes.
Handbuch der Systematischen
Botanik.
By Richard Wett-
1933-1935, two and 3,974 figures; Franz volumes, in its modern lies of this work The value great Deutickte, Leipzig. and original conceptions and its excellent descriptions and
stein,
Wien. 1,152 pages, 709
University
of
Fourth
edition,
plates,
illustrations.
The
Classification of Flowering Plants.
By
A. B. Rendle,
I, Gymnosperms and Monocotyledons. First edition, 1904, 403 pages and 187 illustrations. Volume II, Dicotyledons. First edition, 1925, 636 pages and 279 This work makes no illustrations; Cambridge University Press.
British
Museum.
Volume
pretense of listing all species but gives remarkably fine descriptions of all the families, the morphological tendencies within the It is parfamilies, and the modifications of the family types. ticularly strong in indicating the morphological equivalents of
A TEXTBOOK OF SYSTEMATIC BOTANY
316
highly specialized organs. the entire world.
The Families
Examples are drawn from the
of Flowering Plants.
By
J.
flora of
Hutchinson, Royal
Kew, England. Volume I, Dicotyledons. First edition, 1926, 328 pages and 264 illustrations, with an elaborate diagram of phylogenetic arrangement. Volume II, Monocotyledons. First edition, 1934, 243 pages and 107 illusHutchinson's trations; Macmillan & Company, Ltd., London. work represents the latest general exposition of the flowering It is refreshing in its originality, with a number of proplants. gressive features: a statement of phylogenetic principles; a new phylogenetic scheme (reviewed on page 299) that is bound to proBotanic
Gardens,
voke fruitful discussion; a grouping of the orders and families according to their characters, tendencies, and consequent affinities; an extensive key to families, world- wide in its scope; a concise and well-illustrated description of each family, accompanied
many instances by a distribution map. Flowers and Flowering Plants. By Raymond J. Pool, UniSecond edition, 1941, 428 pages and 211 versity of Nebraska. This book conillustrations; McGraw-Hill Book Company, Inc. tains much of fundamental interest to students of systematic botany and tu amateur botanists who would carry their studies
in
beyond the mere naming of plants. It also presents in the most workable form the principles and system of classification set forth by C. E. Bessey. Emphasis is laid on a study of families, and more than 100 are described rather fully. These are beautifully illustrated, and nearly all are given their floral formulae according to the plan advocated by Clements (see page 40).
REGIONAL FLORAS AND MANUALS of those who wish to identify the flowering own region, many manuals on the local flora have They make no pretense of including all known
For the convenience plants of their been written.
species but aim to be complete for a limited area, generally a state or a group of states. The size of the book is thus kept down, and
much
name of any plant in question than it a great world flora describing all known species. Some of these books, such as 'Gray's Manual/' have been revised and reprinted. Others serve their purpose for a time and go out it is
would be
easier to find the in
THE LITERATURE OF SYSTEMATIC BOTANY
317
of print, to be replaced with others by different authors. Only a few of these will be listed here, for the publication by Blake and Atwood, given below, may be consulted for any desired region. Geographical Guide to the Floras of the World. By S. F. Blake and Alice C. Atwood, U.S. Department of Agriculture, Miscellaneous Publication No. 401 Government Printing ;
Fi.
10f>-
-Range covered by the
Key
to
principal botanical States.
manuals of the United
Numbers on Map
' Gray's Manual of Botany.' 2, Britton and Brown's 'Illustrated Flora.' 4, Rydberg's 'Flora of 3, Small's 'Flora of the Southeastern United States.' 6, the Prairies and Plains.' 5, Rydberg's 'Flora of the Rocky Mountains.' Coulter and Nelson's 'Rocky Mountain Botany.' 7, Woo ten and Standley's 'Flora of New Mexico.' 8, Tidcstrom and Kittell's 'Flora of Arizona and New Mexico.' 9, Tidestrom's 'Flora of Utah and Nevada' 10, Jepson's 'Flowering Plants of California.' 11, Peck's 'Flora of Oregon.' 12, St. 13, Frye John's 'Flora of Southeastern Washington and Adjacent Idaho.' and Rigg's 'Northwest Flora.' 14, Helen Gilkey's 'Handbook of Northwest Pacific States.' of the Flowering Plants.' 15, Abram's 'Flora 1,
Washington, D.C., 1942. Part I lists the floras of Africa, Australia, North America, South America, and islands of the The very large number of Atlantic, Pacific, and Indian oceans. with is well cited local floras annotations, followed by an arranged index. and a author index regional
Office,
Gray's
New Manual of Botany.
by Asa Gray, revised by B. L.
Earlier editions
Harvard University. Seventh edition, 1908, Robinson and M. L. Fernald, Harvard University, 926 pages and
A TEXTBOOK OF SYSTEMATIC
BOTANY
American Book Company. An eighth edition No work of its kind is better known or more used than 'Gray's Manual.' The analytical keys have been thoroughly tested and the descriptions are concise but clear. The 1,036 illustrations; LS in preparation.
illustrations,
though small, are well chosen.
Flora of the Prairies and Plains of Central North America. P.
A. Rydberg,
New York
Botanical Garden.
By
First edition,
by the New York from the Great Lakes to the foothills of the Rocky Mountains and south to 3klahoma. It consists of keys and descriptions similar to those rf the Rocky Mountain flora by the same author but follows the 1932, 969 pages
and 600
Botanical Garden.
illustrations; published
This
flora covers the region
International Rules of Nomenclature.
Flora of the Rocky Mountains and Adjacent Plains. By P. A. Rydberg, New York Botanical Garden. First edition, 1917,
by the author. Rydberg's flora covers a somewhat wider range than Coulter and Nelson's manual and includes many more genera and species. The American Code of nomenclature is followed. New Manual of Botany of the Central Rocky Mountains. By John M. Coulter, University of Chicago, revised by Aven Nelson, 1,110 pages, unillustrated; published
Wyoming. Second edition, 1909, 646 pages, Book Company. This book, of convenAmerican unillustrated; ient classroom size, has proved a highly useful work for a large of
University
area of the country. Manual of the Flowering Plants of California.
Tepson,
University of California.
First
pages and 1,023 illustrations; published dents Store, University of California.
edition,
By
Willis L.
1925,
1,238
by the Associated StuThis book gives an
admirable presentation of the flora of the southwestern part of the country.
The
species are well delineated
and
illustrated,
and
but valuable data are given on the ecology of the different zones and the habitat favorable to each species. Flora of the Southeastern United States. By J. K. Small, brief
New York published
Botanical Garden,
study of the flora
and
is
1933,
1,554 pages, illustrated;
This work is indispensable for a of the southeastern fourth of the United States
by the author.
admirably executed.
The
latest edition
International Rules of Nomenclature.
makes use
of the
THE LITERATURE OF SYSTEMATIC BOTANY
319
TAXONOMIC TREATMENT OF LIMITED GROUPS
A
considerable
number
in restricted fields of
of books and papers have been written taxonomy, sometimes taking the form of
monographs of certain natural groups genera, families, etc. and sometimes presenting such miscellaneous groups as appeal to certain classes of readers
The
trees, flowers, edible plants, etc.
Silva of North America.
By
Charles S. Sargent, Arnold
Arboretum, Harvard University. First edition, 1891-1902, fourteen volumes containing 2,185 pages and 740 splendid, fullpage lithographic plates; Houghton Mifflin Company. Sargent's 'Silva' is one of the finest pieces of work produced in this counThe trees are considered by families, with some attention to try. the interrelationships of genera and species. The synonymy of the specific names is given, with excellent descriptions of each species, and information on ecology and economic importance. The illustrations with their fine details are unsurpassed. Manual of the Trees of North America. By Charles S. Sargent, Arnold Arboretum, Harvard University. Second edition, 1922, 910 pages and 783 illustrations; Houghton Mifflin Company. Since its first appearance this work has been the standard condensed reference book on the trees and shrubs of this It describes both native and introduced species, country. following the Engler and Prantl arrangement national Rules of Nomenclature.
Manual
and the
Inter-
Trees and Shrubs Hardy in North America. By Second edition, 1940, 996 pages, unillustrated; The Macmillan Company. This book classifies and describes more than 2,300 species of woody plants with numerous varieties and hybrids and gives distribution zones and notes on adaptability. Timbers of North America. By Samuel J. Record, Yale Uniof
Alfred Rehder, Arnold Arboretum, Harvard University.
versity.
& Sons,
First edition, 1934, 196 pages, illustrated; John Wiley The strength of the book lies in its discussion of the
Inc.
anatomy and
histology of the different kinds of woods.
It con-
key of twenty-eight pages for the identification of woody species, based on general and microscopic characters of the wood, by which the species can be determined without regard to external morphology. -*It has good popular descriptions of more than seventy species, giving distribution, abundance, and economic tains a
uses.
A TEXTBOOK OF SYSTEMATIC BOTANY
320
Winter Botany. By William Trelease, University of Illinois. Third edition, 1925, 438 pages and over 300 illustrations; published by the author. The book is of convenient pocket size, and, while
semipopular,
analytical keys
shrubs,
it
is
highly
authoritative.
It
contains
and
and woody
excellent descriptions of most of the trees, vines in their winter condition. It is excellent
and the better informed amateur botanists. Northern Rocky Mountain Trees and Shrubs. By J. E. Kirkwood, State University of Montana. First edition, 1930, 340 pages, 35 plates and 87 text figures, mostly original; Stanford In readable style and with scientific accuracy University Press. this book describes practically all the trees and other woody plants of the area covered, with information on the economic
for the use of students
importance and points Keys are provided for
of peculiar interest
applying to each.
classification into families, genera,
and
species.
Gymnosperms Structure and Evolution. By Charles Joseph Chamberlain, University of Chicago. First edition, 1935, 484 pages and 396 illustrations; University of Chicago Press. Each of the seven orders of gymnosperms is thoroughly discussed and and
illustrated,
is given to the phylogeny of highly authoritative and written in an
especial attention
The book
each group.
is
interesting style.
Monocotyledons. By Agnes Arber, Balfour Laboratory, Cambridge, England. First edition, 1925, 258 pages and 160
Cambridge University Press. A well-rounded, of the morphology and affinities of the group. discussion thorough While the work is not primarily taxonomic, it contains much
illustrations;
information upon which the taxonomy of this great group must be It is a fine example of this type of monograph. based.
Manual cock, U.S.
of the Grasses of the United States.
Department
of Agriculture.
By
A. S. Hitch-
First edition, 1935, 1,040
pages and 1,696 illustrations; Government Printing Office, WashAn indispensable work to students of agrostology. ington, D.C. It contains discussions of grass morphology and economic uses, keys, descriptions of species and other groups, and a very full glossary of the technical terms used in this field. North American Cariceae. By Kenneth Kent Mackenzie. 1940, two large volumes, 547 pages, profusely with keys for identification in a separate pamphlet;
First edition, illustrated,
THE LITERATURE OF SYSTEMATIC BOTANY
321
published by the New York Botanical Garden. The most nearly complete and satisfactory descriptions of the species of Carex that has yet been published. Distribution and habitats are included.
A Monograph of the Section Oreocarya of Cryptantha. By Edwin Blake Payson, Ann. Mo. Bot. Gard. 14: 211-347, 1927. This paper represents a thorough and well-balanced study of a It includes morphological distinctions between this subgenus. and related subgenera and between the included species, geographical distribution from a world standpoint, phylogeny and ' that is evolution, even approaching the 'new systematics It has a philreceiving so much attention at the present time. osophic tone throughout. Poisonous Plants of the United States. By Walter Conrad Muencher. First edition, 1939, 266 pages, illustrated; The Macmillan Company. Following a fifteen-page introduction on of different methods classifying poisonous plants, those found in this country, of which there are about 400, are classified according to plant families. Under the discussion of each are given the scientific and common names, the description, the distribution and habitat, and statements concerning the poisonous principle
and
its effects.
Taxonomy; The North American Species of Artemisia, Chrysothamnus, and Atriplex. By Harvey M. Hall and Frederic K. Clements, The Carnegie Institution. First edition, 1923, 355 pages, 47 text figures and 58 plates.
The Phylogenetic Method
in
Publication No. 3564; Carnegie Institution of Washington, D.C. Following an introduction of thirty pages on general principles of
taxonomy, the three genera mentioned
in the title are discussed.
The of treatment of the three genera is similar. for are the subdivision affincriteria used characters or described,
The method
the genera with related genera are discussed, and the interEach genus is divided nal relationships are shown by diagrams. What is more striking, each into into sections, and these species. to its recognizable with reference species has been studied and in some many in others the species varieties, which are few
ities of
more
These subspecies are designated trinomially. that where such fine subdivisions are recognized inevitable and expressed in phylogenetic diagrams there will be some differplastic ones.
It is
ences of opinion
among the
critics,
but these two workers have
A TEXTBOOK OF SYSTEMATIC BOTANY
322
indicated ideals that others could well follow in monographing generic and other groups.
CULTIVATED AND ECONOMIC PLANTS
Most descriptive manuals or floras of the different regions do not include introduced species that are under cultivation unless they have escaped and become established with the native flora. The identification and study of the cultivated plants have been facilitated by a few important works. It is quite impossible to for books of the identification all keep plants cultivated in America up-to-date for the reason that new species are constantly being originated and others are being introduced from abroad. Origin of Cultivated Plants. By A. P. dc Candolle, Academy of Science of the Institute of France. First edition, 1882, 468 D. unillustrated pages, Appleton-Century Company, Inc. of a some discussion Following thirty pages on the character of the to a such discussion, the author traces many evidence applicable ;
varieties and species grown in different parts of the world back to While considerable evidence has ancestral forms growing wild.
been brought out since the book was written concerning the origin of certain crop plants, most of the conclusions still hold. Studies on the Origin of Cultivated Plants. By N. Vavilov, Leningrad, Bull. 2 of Applied Botany and Plant-Breeding, 16, This 1926, 108 pages, 6 illustrations, and 7 distribution maps. paper presents modern methods of determining the place of origin and ancestral forms from which cultivated plants have
The older methods of comparing cultivated varieties with similar wild ones of the vicinity and of using archaeological records are not ignored, but to these are added what the author designates as the botanical method, which includes genetic and cytological evidence and lays especial stress on the hypothesis that around the point of origin of a species much minor variation will be found among the individual plants, while in other regions to which it has spread there is greater uniformity. Evidence is also shown that certain species once regarded as weeds were later arisen.
domesticated.
Manual
of Cultivated Plants.
By
L. H. Bailey, Cornell Uni-
and 14 illustrations; The Macmillan Company. The book contains in compact from analytical keys and descriptions of most species and many variversity.
First edition, 1924, 851 pages
-
THE LITERATURE OF SYSTEMATIC BOTANY
eties of plants that are cultivated in the
323
United States for use or
up-to-date in its taxonomy and nomenclature and gives some information concerning the origin of many of the forms
pleasure.
It is
treated.
Standard Cyclopedia of Horticulture. By L, H. Bailey. Reissue of second edition, 1935, three volumes, 3,639 pages, profusely illustrated;
and descriptions
The Macmillan Company.
of the cultivated plants of the
A
classification
United States and
Canada, with information concerning their culture and use. Hortus Second. By L. H. Bailey and Ethel Zoe Bailey. Second edition, 1941, 778 pages, illustrated; The Macmillan Com-
A handy reference to the cultivated plants of America, names and descriptions and concise information on their use. Standardized Plant Names. By Harlan P. Kelsey and
pany.
giving
Second edition, 1942, 675 pages; published Horace McFarland Company for the American Joint Committee on Horticultural Nomenclature. This book lists more than 90,000 names of economic plants and plant products. The botanical and common names are given, accompanied by lists of More than 8,000 new common names have cultivated varieties. been added, and efforts have been made to reduce confusion due to use of the same common name for different species. Herbals, Their Origin and Evolution. By Agnes Arber. Second edition, 1938, 326 pages, illustrated; The Macmillan Company. An historical account of the development and use of drug plants from 1470 to 1670. William A. Dayton.
by
J.
Plants Useful to Man. By W. W. Robbins, University of SecCalifornia, and Francis Ramaley, University of Colorado.
and 235 illustrations; The Blakiston readable In style the authors present the origin, very Company. of the most important economic and uses distribution, culture, ond
edition, 1937, 422 pages
plants of the United States and many others grown in the tropics For the most part the plants are grouped accord-
and elsewhere.
ing to natural families.
Range Plant Handbook. By the Forest Service of the U.S. Department of Agriculture. First edition, about 700 pages, illustrated; Government Printing Office, Washington, D.C., A large number of grasses and other range plants are 1937. Both botanical described in nontechnical terms and illustrated. and common names are given. There are discussions of groups
A TEXTBOOK OF SYSTEMATIC BOTANY
324
and individual species giving information concerning abundance, and value.
their range,
NONTECHNICAL FLORAS The phase
of botany that most appeals to the amateur is the and naming of the wild flora. Few amateurs give recognition attention to any other branch of botany, while thousands seek to learn the names of at least the most conspicuous plants. Some amateur systematists take up the subject in the most superficial
way, being content with almost any common name that they by word of mouth and never really examining plants at all, while others become remarkably proficient in all but the most
learn
difficult groups.
aid the worthy attempts of those who seek to learn the names of the wild plants for their own pleasure a considerable number of books have been written. Such a task is by no means
To
and most such books have not been very successful. Various devices have been employed to aid the layman in identifiGeneral descriptions alone are almost total failures. cation work.
easy,
Technical descriptions discourage all but the most determined. Semipopular keys are quite valuable to the more studious amateurs and lead naturally to semipopular descriptions which are sufficient for species that are clear-cut and few in a genus. Illustrations are being more and more used and are valuable to supplement keys and descriptions. They have some weaknesses.
Good
illustrations are so expensive that only a small percentage
of the species can
be honored by them.
Furthermore,
many
species are so much alike in general appearance that a given picThere is no ture may apply equally well to several of them.
convenient way of associating the plant in question with its picture in a profusely illustrated work except by keys; hence the superficial worker spends much time rambling through the book hunting for the desired illustration, which may not be there at all. There is no easy road to success in identifying plants, and all who expect to become proficient must master the morphology and terminology required to use technical manuals. It has been
observed that the amateur generic and
who has not
specific botanical
names
the courage to learn
lacks also the persistence
required to identify plants. To simplify the work of identification, popular floras are usually
THE LITERATURE OF SYSTEMATIC BOTANY restricted geographically
and
hence many plants omitted from the book. species;
325
treat only the more conspicuous be collected that have been
will
Field Book of American Wild Flowers. By F. Schuyler Mathews. Revised edition, 1912, 587 pages, 24 colored plates, and more than 300 line drawings; G. P. Putnam's Sons. For the eastern half of the United States this book serves as a good guide for the amateur. The plants are arranged by families, and most of the prominent species are described and illustrated. Two keys
specimen with its description: a on the more obvious morphological and botanical names are given, the
facilitate the association of the
color key, and a key based Both common characters.
latter following the International Rules. Rocky Mountain Flowers. By F. E.
Clements and Edith
S.
Clements. Third edition, 1928, 390 pages and 47 plates, more than half of which are colored; The li. W. Wilson Company, New York. The presentation is semipopular, with numerous keys and Families and genera are described, and some fine illustrations. of the species are listed but not described. The distinctive feature of the work is a flower chart that aids in the location of families by lines and formulae that indicate different types of floral structure. Some skill is required to use this chart but it is very helpful when mastered.
North American Mountains. By Julia of Canada. First edition, 1915, 383 Club Henshaw, Alpine 83 a fourth of which and are colored; Robert M. plates, pages McBride & Company, New York. The book is particularly The key applicable to Canada and the northern United States. is not of an analytical type, being merely a synopsis, but as a
Wild Flowers
of the
device for aiding the reader in placing his specimen the plants are grouped according to flower colors, a method that in most cases
narrows the search down to a point where the desired picture can be found with some readiness. The illustrations are excellent and both technical and popular descriptions are given, with a liberal admixture of sentiment. Wild Flowers. By Homer D. House. Imperial edition, 1936, 362 pages and 264 full-page colored illustrations; The Mac-
Company. An interesting three-page introduction is followed by twenty-three pages of descriptive matter and definimillan
tions applying to flowering plants, which aid in the use of the keys
A TEXTBOOK OF SYSTEMATIC
326
to the species. The plants are arranged cotyledons to Compositae.
American
Plant
Names.
by
Willard
By
BOTANY families
N.
from mono-
Clute.
Third
1940, 285 pages with supplement; published by the list of the scientific names of author at Indianapolis, Indiana. edition,
A
the wild plants of the northeastern quarter of the United States but somewhat applicable to a wider range. For each species the
corresponding
common names
are given.
PALEOBOTANY Paleobotany holds the joint interest of geologists, botanists, zoologists because of its record of conditions on the earth durNot only does it shed much light on the phyloing past ages. genetic relationships of plants, but it indicates in many cases the climatic and other environmental conditions under which the development of the plant and animal kingdoms, including man, took place. Studies in Fossil Botany. By D. H. Scott, Royal Botanic Gardens, Kew, England. Third edition, 1920, two volumes containing 880 pages and 326 illustrations; A. & C. Black, Ltd., London. Volume I covers the pteridophytes and lower plants and Volume II the higher plants. We have here an authoritative treatment of the subject by a veteran writer. Not only are the paleontological findings recorded and summarized, but philosophical discussions on evolutionary relationships are presented. While the evidences used are obtained chiefly from the rocks, the morphology of existing plants has not been ignored. The Origin of a Land Flora. By F. O. Bower, University of Glasgow. First edition, 1908, 727 pages and 261 illustrations; Macmillan & Company, Ltd., London. The author here presents
and
origin of the higher plants and the of land above the waters that had the presence part played by it. In covered presenting his evidences the author has long assembled data of much value aside from their bearing on the
an hypothesis concerning the
topic of the book. Primitive Land
Glasgow.
Plants.
By
F.
O.
Bower,
University
of
First edition, 1935, 658 pages with 465 illustrations; ' Company, Ltd. This book is not a revision of The
Macmillan &
Land Flora ' by the same author, but in a somewhat way the same subject matter is presented, with the
Origin of a different
THE LITERATURE OF SYSTEMATIC BOTANY added information gained
in nearly
30 years of research by
327
many
investigators.
The Evolution
of the Land Plants. By Douglas Houghton Campbell. First edition, 1940, 731 pages, 351 illustrations; Stanford University Press. The book presents a critical discus-
sion of phylogenetic relationships
among the higher categories of bryophytes, pteridophytes, and spermatophytes, based not only on paleobotany but bringing in morphological studies of living and other lines of evidence. Plant Life through the Ages. By Albert C. Seward. Second edition, 1933, 603 pages, illustrated with nine reconstructions of ancient landscapes; The Macmillan Company. A geological and plants
botanical retrospect, not too technical for general use. Paleobotany: A Sketch of the Origin and Evolution Floras.
of
By Edward W.
Berry, Johns Hopkins University, Ann. A 1918, 119 pages and 42 illustrations.
Rpt. Smithsn. Inst. concise account, suitable to the needs of botanical students,
sum-
marizing our knowledge of fossil plants, especially the pteridophytes and spermatophytes. Valuable diagrams are given on the prevalence of different groups during past epochs. Plants of the Past; a Popular Account of Fossil Plants. By Frank H. Knowlton, U. S. Geological Survey. First edition, 1927, 275 pages and 90 illustrations; Princeton University Press. This book, from an authoritative source, gives the general reader a clear idea of plants that have existed on the earth at different It also geological periods and the reasons for changes in flora. of to animals has chapters on the importance plants prehistoric
and on coal production. Tree Ancestors. By Edward W. Berry, John Hopkins UniFirst edition, 1923, 270 pages and 48 illustrations and versity. maps; The Williams & Wilkins Company. A discussion of the past and present status of some of the most important families of woody plants, presenting valuable information in a most readable The book gives clear-cut explanations of the peculiar style. distribution of many species, the survivors in favored localities of once cosmopolitan races.
INDEXES, CATALOGUES, ETC.
From time advancement
to time works have been written summarizing the that has been made in the study of plants. These
A TEXTBOOK OF SYSTEMATIC BOTANY
328
are of especial value in locating the literature on different phases of the subject.
Thesaurus Literaturae Botanicae. By G. A. Pritzel, Berlin. Second edition, 1872, 254 pages, unillustrated F. A. Brockhaus, ;
The chief botanical publications up to 1872 are listed under the names of the authors, arranged alphabetically, and in a About 15,000 references are later section classified by subjects. Leipzig.
given.
Genera Siphonogamarum. Harms,
Berlin.
By
C. G. de Dalla Torre and
II.
First edition, 1900-1907, 921 pages unillusa valuable aid in the tracing of generic synonymy.
This is Following a list of families of spermatophytes some 637 pages are devoted to lists of genera, arranged by families and subfamilies, and showing the sections of the genera, if such occur. The synonymous names of genera and sections are given, with dates and The last part of the book is taken up by a huge index citations. of 284 pages containing all the generic and sectional names used
trated.
in the text.
The work
follows the Engler system,
Index Kewensis Plantarum Phanerogarum. By B. D. Jackson, Kew Herbarium, under the direction of Jos. D. Hooker. The original work (1893-1895) consisted of four large volumes having a total of 2,567 pages, unillustrated, and to these have been added nine large supplements; Oxford University Press. This monumental work lists all species described since 1753 under their genera, which are arranged alphabetically, and each specific
name
is accompanied by a reference to the original publication. Nonvalid synonyms are in italics and referred to the accepted name. It is indispensable to the research worker in taxonomy of
flowering plants.
Bradley Bibliography. By Alfred Rehder. Five volumes. Publication No. 3 of the Arnold Arboretum; Riverside Press, 1911-1918. A guide to the literature of the woody plants of the world that were described before the beginning of the twentieth century.
Index Londinensis to Illustrations of Flowering Plants, Ferns,
and Fern Allies. By Otto Stapf and O. C. Worsdell. A sixvolume set published by the Oxford University Press. Edited by Stapf up to 1921, with a two-volume supplement by Worsdell from that date to 1935. It is an amended and enlarged edition of PrezeFs ' Alphabetical Register ' continued to a later date.
THE LITERATURE OF SYSTEMATIC BOTANY The Gray Herbarium Card Index.
A
Herbarium.
set of cards listing all
329
By the Staff of the Gray new names and new com-
binations for genera, species, varieties, and forms of flowering Issued plants, ferns, and fern allies of the Western Hemisphere.
quarterly to subscribers. About 258,000 cards have been pubIt is invaluable for research work in plant to date.
lished
taxonomy. North American Flora. Published by the New York Botanical Garden, from 1906 to date. Thirty-four volumes were published
up to
This great work
1940.
of all the wild plants of
is
intended to furnish descriptions
North America.
MISCELLANEOUS The simple grouping used of
systematic
botany
in this chapter for the literature
leaves
some important
publications
unclassified.
A
Glossary of Botanical Terms. By B. D. Jackson, Linnaean Society of London. Seventh edition, 1928, 481 pages, unillustrated;
J.
B.
Lippincott
Company. Most manuals include most circumstances these are
glossaries of the terms used, and in sufficient for the purpose intended.
Many
technical terms used
in botanical science are not, however, included in these limited lists. Furthermore, some terms require a fuller discussion than space will permit in connection with a crowded manual. This book fills the needs just indicated in an admirable way.
Glossary of Botanical Terms Commonly Used in Range Research. By W. A. Dayton, U.S. Department of Agriculture While Miscellaneous Publication No. 110, 40 pages, illustrated. this pamphlet is intended primarily for use in forestry work, it is very suitable and convenient for students in systematic botany. Outlines of the History of Botany. By R. J. Harvey-Gibson, University of Liverpool. First edition, 1919, 274 pages, unillustrated; A.
pany.
A
&
C. Black, Ltd., London, and The Macmillan Comwell-balanced discussion of the development of
botanical science, including especially
its
taxonomic, morpholog-
It is authoritative, unprejuical, and physiological aspects. in well suited to student use. a and executed style diced, Native American Forage Plants. By Arthur W. Sampson, University of California. First edition, 1924, 435 pages and 200 The subject is treated illustrations; John Wiley & Sons, Inc.
330
A TEXTBOOK OF SYSTEMATIC BOTANY
with especial reference to the Rocky Mountain and Pacific The regions but applies in a measure to the entire country. treatment is particularly effective and convenient. The plants are grouped by families, and the more important species are Valuable information is given concerning clearly described. their distribution, abundance, palatability, and nutritive value. Summary tables facilitate the finding of desired information. Useful Wild Plants of the United States and Canada. By
and 74 Company, New York. This book is written in semipopular style, using both common and It summarizes our knowledge of the past and botanical names. present use of plants by the Indians and the white men that Charles F. Saunders.
illustrations;
1920, 275 pages
First edition,
Robert M. McBride
&
them. In addition to assembling the knowledge acquired by others, the author adds many of his own observations. Special emphasis is laid on the use of plants for food, but followed
medicinal and other properties are considered also. Manual of Weeds. By Ada Georgia, Cornell University. First edition, 1914, reprinted in 1940, 593 pages and 386 illus-
The Macmillan Company. Following a chapter on the fundamental principles of weed development, dissemination, and control, several hundred weed species are described and discussed The arrangement is by families, and both common and botanica names are given. Under each species are given the source, means trations;
of propagation, season of
development, distribution, and habitat
The methods of control are briefly indicated. Taxonomy of the Flowering Plants. By Arthur M. Johnson, University of California at Los Angeles.
pages and 478
original illustrations; D.
First edition, 1931, 864 Appleton-Century Com-
pany, Inc. This book is written as an aid to teachers and students of taxonomy. Part I is chiefly concerned with morphology in its relation to
angiosperms.
taxonomy.
No
and more space
Part II
is
a description of groups of
made
of describing every species, pretense is therefore available for the species and larger is
groups that merit special attention. Prantl system is followed.
In general the Engler and
INDEX Numbers
in bold-face indicate pages bearing illustrations. specific names are in italics.
Generic and
Ancestral forms, evidence loss of, 241 Abies, 84
Aceraceae, 168
Angelica, 187
Achillea, 189
Angiosperm
Achyronchia, 121 Aconitum, 100, 102 Acorns, 200, 201 Actaea, 99, 102
status
relation of
283
present
302 need
gymnosperms
to,
91
Agropyron, 210 Agrostemma, 120, 121 Alisma, 196, 196 Alismaceae, 195 Allenrolfea, 122 Allium, 196 Alnus, 179 Althaea, 104
subclasses of, 137 Antirrhinum, 140, 141
Apetalae, 300
Apium, 184 Aporocactus, 163 Aquilegia, 99, 102
Araceae, 200 Arachix, 152, 154
Arceuthobium, 167
relation of system-
to,
classification,
origin of, 12, 74, 91 (See also frontispiece)
Affinities, natural, 240, 281,
Amateur botany,
of,
revision of, for, 303 Angiosperms, characters of, 76
Aeschynomene, 153 Aesculus, 175
botany
237
Anemone, 99 Anethum, 186
Acer, 169, 170
atic
of,
Arctostaphylos, 128
7
Ambrosia, 189, 192 Ambrosiaceae, 189 Amelanchier, 148 Amentiferae, 91, 172
Arisaema, 200, 201 Aristotle, 282 Armoracia, 119 Artemisia, 189
American Code, of botanical nomenclature, 230-231 origin of, 230
Arum, 201
Artificial groups, 9, 269, 285,
Asclepiadaceae, 133, 134, 135 Asclepias, 133, 134, 135
Ammiaceae, 184 Amorpha, 153
Asparagus, 196 Aster, 189 Astragalus, 156 Atriplex, 123 Authentic material, 233 Autophytic plants, 75
Amorphophallus, 200 Amygdalaceae, 149 Anacardiaceae, 171 Anacardium, 171
Analogous structures, 243, 267, 268
A vena,
Ancestral forms, 24
331
205, 206
301
76,
A TEXTBOOK OF SYSTEMATIC BOTANY
332 Azalea, 128
Candolle, A. P. de, 286, 287, 307, 312 Capitals, for generic names, 235
Azorella, 184
for specific epithets, 235 Caprifoliaceae, 188
B
Capsella, 118, 119
Bambusa, 205, 210
Capsicum, 137 Carduaceae, 189 Carex, 203, 204
Barriers to crossing, 253
Bauhin, Gaspard, 221, 284 Bennettitales, 77, 80, 92 Beiitham, G., and Hooker,
1).,
taxonomy by, 288
of
system
J.
Carpels, primitive condition of, 272 taxonomic value of, 272, 274
Car urn, 186
Berberidaceae, 97, 98, 99
Carya, 172
Berberis, 98, 99
Caryophyllaceae, 120, 121 Castalia, 103 Castanea, 175 Castanopsis, 176 Castilleja, 140 Categories used in taxonomy, 249, 288 how distinguished, 269 made to fit plants, 249 name endings of, 250 not uniform in size, 250
Bessey, Charles
comparison influence
K, 292 with Kngler, 296
of,
of,
on botany, 2
phylogenetic conceptions 297, 298
system of 296
classification
of,
by
;
296292-
Beta, 121, 122, 123
Betula, 179, 180, 182
Betulaceae, 179
Binary generic names, 221 Binomial system, of nomenclature, 284 indicates relationship, 217 origin of, 220 Biotype, 264 Boraginaceae, 139, 140 Botanical terms, glossary
of, 55,
329
283,
subspecific, Cattleya, 213, Celtis,
256-259 214
106
Cenospecies, 263 Centaurium, 131 Central Kurope, taxonomy
283
Cephalanthus, 187 Cerastium, 120, 121
Brassica, 117-119
Ccrcocarpus, 147
Brassicaceae, 117
Cesalpini,
Bromus, 206, 210 Browse, Betulaceae, 182 Caprifoliaceae, 188 Rosaceae, 147 Salicaceae, 127 Buds, terms pertaining to, 58
in,
Ccphalanthera, 213
A.,
taxonomic work
of,
282 Cestrum, 139 Chamaesyce, 113 Chamberlain, C.
J., classification
gymnosperms by,
77,
of
80
Characters used in taxonomy, 264
-
276
C Cactaceae, 163 Calochortus, 197
Calonyction, 135 Caltha, 100
Camelina, 118, 119
clear-cut vs. intergrading, 265, 266 intergrading, 265, 266
major and minor, 244, 264 single vs. combinations of,
280
stability of, 265 vegetative vs. reproductive,
Chart,
floral, 40, 42,
43
265
INDEX Congresses, Paris, 228
Cheiranthus, 117, 119
Vienna, 229
Chenopodiaceae, 121, 122, 123 Chenopodium, 121, 122 Chrysanthemum, 189 Cichoriaceae, 189 Cicuta, 186, 187 Cimicifuga, 99, 100 Cinchona, 187 Cirsium, 189
Coniferales, 75, 77, 79, 83 families of, 84-89
Coniferophytes, 79 Conopholis, 142 Conringia, 118 Convallaria, 196
Convalhiriaceae, 196
Citrullus, 161
112 Cladophyll, 267 Classics, early, 306
r-iYrws, 111,
C Classification,
333
basis used for,
8,
10,
242
Convolvulaceae, 135, 136, 137 Convolvulus, 135, 136, 137 Corallorrhiza, 213 Cordaitales, 79, 82 Cornaceae, 182 CornuSj 183
237-242, 244 evolutionary systems of, 288 of flowering plants, 75, 76 ideals in, 8
Corylus, 179, 181
methods
Crossing, barriers to, 253
difficulties in,
of,
9
phylogenetic,
9,
242, 289, 292
pre-evolutionary, 240, 281-287 revolutionized by evolution, 19 unit of, 251 Clematis, 99, 102 Clements, F. E., descriptive of,
194
Cucumis, 161 Cucurbita, 161, 162
Cucurbitaceae, 161 Cultivated and economic kipressaceac, 88
C up r ess us, 88 Cmcuta, 135, 136 Cycadales, 76, 77, 81, 92 Cycadofilicales, 77, 79 Cycadophytes, 77, 79 Cynoglossum, 139
Cyperaccae, 202 Cyperus, 203
Cypripedium, 213, 214 Cytology, contribution onomy, 260
230 Coffea, 187
Coleus, 145
methods
of,
plants,
322-323 (
Climate, geological, 12-13 Coccolobis, 125 Cocos, 202 Codes of nomenclature, 228-234 American, 223n., 230, 231 Paris, 228, 229 type-basis, 232 Vienna (International Rules), 229-
3,
Cruciferae, 117, 118, 119
method
40
Collecting,
Cotypes, 233 Coulter, J. M., Crataegus, 148
of,
to tax-
46
Compositae, 189 comparison of, with Orchidaceae, 215 Conium, 187 Congresses, international, 228-234 Amsterdam, 234 Brussels, 230 Ithaca, 233 London, 234
D Darwin, Charles,
18,
288
Datura, 139 Daucus, 184
Degeneracy, forms in grasses, 205
of,
26-27
vs. primitive simplicity, 241 vs. specialization,
27
A TEXTBOOK OF SYSTEMATIC BOTANY
334
Delphinium, 99, 100, 101, 102
Ecotype, 263
Descriptions, comparing with, 37
Eichler, A. W., classification system
exceptions to, 36-37 in Latin, 229, 230, 234, 235
Designating authority, parentheses in, 227 Desmodium, 153, 154
ies,
93
origin of, 91 relation of monocotyledons to, 76
Digitally 140
Dodonaeus, binomial usage by, 221
verna,
phylogenetic conceptions, 297, 298
Engler and Bessey, systems parison of, 296
Environment, change effects of, 254
Dioscorea, 137
law by,
287
Engler, A., 290 of, 76,
families of, 94-193
Draba
of classification,
Engelhardtia, 174
Dicotyledons, characters
Louis,
287
system
Dianthus, 120 Dicentra, 116
Dolle,
by, 290 phylogenetic conceptions of, 290 Endlicher, Stephen, anatomical stud-
irreversible-evolution
16, 28,
243
252
com-
in, 12, 13,
15
Ephedra, 89 Epifagus, 142 Epigaea, 128 Epilobium, 160, 161 Epithets, specific, 219n., 220
Dracaena, 196 Drug plants, Araceae, 200 Compositae, 193 Drupaceae, 151 Euphorbiaceae, 115 Labiatae, 145 Leguminosae, 156 Papaveraceae, 117 Ranunculaceae, 102
Eragrostis, 210
Ericaceae, 128, 129, 130 Erodiurn, 108, 109
Eryngium, 184 Erythronium, 196 Escholtzia, 116
Eupatorium, 190, 192 Euphorbia, 113, 114 Euphorbiaceae, 113, 114, 115 Eurotia, 123
Rubiaceae, 187-188 Rutaceae, 113 Scrophulariaceae, 142 Solanaceae, 138 Umbellifcrae, 185 Drupaceae, 149, 160, 151 Drying, artificial heat for, 50 Dugaldia, 192
P/volution, acceptance of doctrine of,
17-19
accomplishments
of,
24
basis for classification in, 10
continuous, 17 evidences of, 10-17
mechanism
E
of,
19-24
parallel, 10
recent productions, 16-17 in relation to taxonomy, 8
Echinocystis, 161
Ecological experiments, 261
reversibility of, 16,
Ecological modifications, 258
trend
Ecologists,
work done by,
Ecology,
relation
of
botany to, 1, 6, 260 Economic significance each family) Ecospecies, 263
of,
291,
53, 261
of,
Evolutionary processes, 23
systematic (See
28
277
under Fabaceae, 151 Fagaceae, 175
INDEX Food
Vagopyrum, 124 Fagus, 175, 176 Families, of dicotyledons, 91-193
gymnosperms, 77-90 monocotyledons, 194-216 of spermatophytes, 77-216 Festuca, 206 of of
Fiber producing plants, 105, 111 Fibrovascular bundles, of angio-
sperms, 76 of dicotyledons, 76, 93 of gymnosperms, 76
monocotyledons, 76, 195 taxonomic value of, 265 Floral chart, 40, 42 of
symbols, 40, 41 Floral diagrams, 38, 39 Floras, nontechnical, regional,
324
316
world, 314 axis of, 67, 68, of, 40,
evolution
of, 92,
272 of,
to,
272 65-71
use of term, 74
Food
Vitaceae, 166 Forage plants, Boraginaceae, 140 Caprifoliaceae, 188
Chenopodiaceae, 123 Compositae, 192 Cypcraceae, 203 Geraniaceae, 109 Gramineae, 209 Juncaceae, 200 Leguminosae, 154 Onagraceae, 161 Umbelliferae, 187 Forestry, use of systematic botany in,
5
Formulae, 40, 41 (See also under each family)
how
272
42
taxonomic value terms pertaining (See also
plants, Rutaceae, 112 Solanaceae, 138 Umbelliferae, 185
Fossils, 11, 12, 13 of grass, 12, 205
Flowers, 65 chart
335
under each family)
plants, Aceraceae, 171
Anacardiaceae, 171 Cactaceae, 165
Chenopodiaceae, 123 Compositae, 192 Convolvulaceae, 137 Cruciferae, 119 Cucurbitaceae, 163
Drupaceae, 151 Ericaceae, 128 Euphorbiaceae, 114 Fagaceae, 178 Gramineae, 209 Grossulariaceae, 159 Leguminosac, 154 Oleaceae, 132 Polygonaceae, 125 Pomaceae, 149 Rosaceae, 147 Rubiaceae, 187
formed, 246 value of, 246 Fragaria, 146, 147 FraxinuSy 132 Fruits, 71 edible, Cactaceae, 165
Drupaceae, 151 Grossulariaceae, 159
Pomaceae, 149 Rosaceae, 147 Rutaceae, 112 Vitaceae, 166 taxonomic value terms pertaining
of,
276
to, 72,
73
(See also under each family) Fruits and seeds, place in keys, 37
Fuchsia, 160
Fumigation of herbaria, 52, 53
Fundamental
principles, genetic,
morphological, 307 Fungi, origin of, 9 relationship with algae, 9
G Galium, 187 Gardenia, 187
309
A TEXTBOOK OF SYSTEMATIC BOTANY
336
Gaultheria, 128
Hans, classification system 298 phylogenetic conceptions of, 298
Hallier,
Gaylussada, 128
of,
Genetics, contributions
of,
to tax-
onomy, 260
Harvey a, 141 Hedysarum, 154
Gentiana, 131
Helianthus, 189, 190
Gentianaceae, 130, 131, 132 Geological climate, 12, 13, 247 Geraniaceae, 108, 109
Heliotr opium , 140
Heracleum, 187 Herbaria, cases earliest, 45
Geranium, 108 Gerardia, 141
Geum, 147
fumigation
Ginkgo, 82, 83
insects in, 52
329 Glycine, 152
Glycyrrhiza, 154, 157
Gnetales, 76, 79, 89, 91
Gnetum, 89 Gossypium, 104, 106 Gramineae, 205-211 Grass-like plants, comparison Gray, Asa, 2, 3 influence of, on botany, 2 species making by, 252 Grossulariaceae, 158, 159
Homologous of,
211
Group, categorical rating of, 255 Groups, dividing, 226, 255 uniting, 226
Gymnosperms, characters of, 76 classification of, by Chamberlain, 79
general appearance
88 302 protection of, 52 purposes of, 45 use of, 46 Heuchera, 206 Hevea, 114 Hibiscus, 104 Holchus, 205, 210 organization
Glossary, of botanical terms, 55, 283,
of,
77
geological position of, 13, 78 (See also frontispiece) orders of, 77-90
of,
of,
structures, 267, 268
Homonyms, 224 Honey plants, Caprifoliaceae, 189 Cruciferac, 119
Ericaceae, 128 Labiatae, 145
,
Leguminosae, 155 Polygonaoeae, 125 Pomaceae, 149 Salicaceae, 127
Hooker,
J. D.,
288
llordeum, 210 Hoya, 133
Hutchmson, ceptions
J.,
of,
phylogenetic
299
principles of, 244, 299, 300
origin of, 13, 77 relation to angiosperrns, 74, 76, 91
Hyacinthus, 196 Hydrangea, 157
strobilus of, 74, 76 (See also under each order)
Hydrastis, 102
Gypsophila, 120
52
52
of,
noted examples
Ginkgoales, 76, 79, 82 Gladiolus, 211
77,
for,
Hydrocotyle, 184 Hylocereus, 163
Hyobanche, 141 Hyponyms, 225
H Ernst H., recapitulation law by, 15, 243
Haeckel,
Hairs, kinds of, 62
taxonomic value
Iberia, of,
271
119
Identification, keys for, 32
con-
INDEX manuals methods used in, 30 no short cut to, 30
Identification,
specimens suitable
for,
for,
Implements for studying Indexes, 327-329
Larix, 84
31
31
Lathyms, 152, 163 Latin diagnosis, 229, 230, 234, 235 Latinized names, 219
plants, 31
Lawrence, G.
M., and theory of compound ovary,
273, 274
taxonomic value of, 271 terms pertaining to, 63, 65 (See also under each family) Intergrading characters, 36, 266 Interim committee, 234 International congresses, 228-234 International rules, digest
II.
evolution of
Inflorescences, 63, 64
of,
234-
236 Ipomoca, 135, 136 Iridaceae, 211, 212 7m, 211 Isotypes, 233 Iva, 193
Jasminum, 132 Juglandaceae, 171 Juglans, 172, 173 Juncaceae, 199 Juncoides, 199 Juncus, 199 JimiperuSj 88, 89 Jussieu, A. L. de, system of classification,
337
286
Leaves, 58
taxonomic value of, 271 terms pertaining to, 58-63 (See also under each family) Lectotypes, 233
Ledum, 130 Leguminosae, 151-163-166, 166, 157 Lepidium, 120 Leptotaenia, 187 Lespcdcza, 153 Leucothoe, 130 Ligmtrum, 132 Liliaceae, 196 Lilium, 196, 197 Limited groups, taxonomic ment of, 319 Linaceae, 109, 110, 111 Linaria, 140 Linnaea, 188 Linnaeus, Carolus, 221, 286 Lirntm, 109, 110 Liriodendron, 96, 97 Lithocarpus, 176 Loefiingia, 121
Lonicera, 188
K Kalmia, 128, 129, 130 Kedrostis, 161
Keys, botanical, how made, 32 bracket or parallel, 33, 35-36 indented, 33-34 structure of, 33 Kochia, 121
Loranthaceae, 167 Lumber, Aceraceae, 169 Betulaceae, 181 Cupressareae, 88
Drupaceae, 151 Fagaceae, 176
Gramineae, 210 Juglandaceae, 174 Magnoliaceae, 96 Oleaceae, 132 Pinaceae, 85 Pomaceae, 149 Salicaceae, 127
Labiatae, 144, 145 Lactuca, 189, 193
Lappula, 140
Taxodiaceae, 87 Ulmaceae, 108 Lunaria, 119
treat-
A TEXTBOOK OF SYSTEMATIC
338
BOTANY
Lupinus, 152, 156
Mutation, causes
Luzula, 199
Myosotis, 140
of,
22
Lychnis, 120
N
Lycium, 138, 139 Lycopersicon, 137 Lysichiton, 200
Names, botanical or
M
tid vantages of,
219-
221
authority for, 226, 230n. binary generic, 221
Mabea, 114 Magnolia, 95, 96 Magnoliaceae, 94-96, 97 Magnoliales, 299 Mahonia, 98 Major characters, 244, 264
binomial, 217, 220
disadvantages 219
of,
222
generic,
222-225 and nature, 219 rejection of, 223-225 specific, 220 iionvalid,
265 stability of, 265 Malaceae, 148 Malvaceae, 104, 106 Manihot, 114 Manuals, 31, 316-318 revision of, need for, 303 Marrubium, 145 Mathiola, 119
origin
clear-cut,
valid, 222, 227, 229 validity vs. legitimacy of, 225
varietal,
common,
256 217
30,
authority for, 218, 219 origin of,
217
standardized, 219
Medicago, 152, 154 Melanthacea< 196 Mentha, 145 Menziesia, 130 Mertensia, 140 Metonyms, 223
synonyms for, 219 value of, 218 weaknesses of, 218 family, 250 generic, 219 ordinal, 250
Mez, Carl, 247 phylogenetic conceptions
of,
248
Mimosa 153
220 256 Nelnmbium, 103 Nepeta, 145 Nicotiana, 137 Nodules, 152 Nomenclature, binomial system of, 217, 220, 284 definition of, 4 digest of rules for, 234-236 effects of rules for, 236 preceded taxonomy, 281 relation of taxonomy to, 1, 217 type-basis code for, 232 specific,
varietal,
,
Mimulus, 140, 141 Minor characters, 265, 266 Modification, definition
of,
264
Monocotyledons, 76 characters
scientific,
226
of,
195
families of, 194-216 origin of, 194 relation of, to dicotyledons, 76 Monophyletic origin, 74, 77, 194, 303
Monotropa, 128, 130 Monotropaceae, 128 Monstera, 200 Morphological discoveries, 287 Morphological indicators, of phylogeny, 243, 276-280 difficulties in applying, 244
Nomina
conservanda, 229, 230, 234,
236
Notebook, field, 54 Nuphar, 103
INDEX Nuts, Anacardiaceae, 171 Betulaceae, 181 Drupaceae, 151
339
Oxyria, 124 Oxytropis, 165
Fagaceae, 176 Juglandaceae, 174 Nymphaea, 103 vascular bundles in, 195 Nymphaeaceae, 102, 103, 104 Nyssa, 183
Paeonia, 99, 102 Paleobotany, 241, 246, 326, 327 contribution of, to taxonomy, 259 relation of systematic
botany
to,
6
O
Paleontological records, 12, 13, 246-
247 Paleontology, 24, 247
Odontites, 141
Oenothera, 160 Oil, 105, 111, 114, 132,
Palmaceae, 202 Panicum, 206
145
Olea, 132
Papaver, 116, 117
Oleaceae, 132
Papaveraceae, 116, 117
Onagraceae, 159, 160 Ontogeny, 15 Opuntia, 163, 164 Orchidaceae, 212-215 comparison of, with Compositae, 215 Orders, of gymnosperms, 77-84, 89
Papilionaceae, 151 Parasitic plants, 75, 140, 142, 167,
Origin, of angiosperms, 13, 91 of binomial system, 220
Parthenotissus, 165
of botanical
names, 219
of cotyledons, 194 of cultivated plants,
of
ity,
227
Paspalum, 206
(See also frontispiece)
homonyms, 225 hyponyms, 225
Petroselinum, Petunia, 139
78
polyphyletic, 74, 77, 194,
184
Phaseolus, 152, 153 Philadelphus, 157
of monocotyledons, 194
of
Parentheses, in designating author-
Pelargonium, 108, 109 Penistemon, 140 Peperomia, vascular bundles in, 195 Perianth, taxonomic value of, 274
of land flora, 326 of metonyms, 223
of
Paratypes, 233
Pastinaca, 184, 185 PediculariSy 141
322
of dicotyledons, 91 of gymnosperms, 13, 77, of
213 Parasitism, 27, 142, 277
300
synonyms, 222 typonyms, 223
Phleum, 205 Phoenix, 202 Phoradendron, 167, 168 Phylogenetic conceptions, of Bessey,
293-296
Orobanchaceae, 142, 143, 144 Orobanche, 143, 144
Eichler, 290, 300
Oryza, 205
Engler, 291, 292, 300
300
Osmorhiza, 187
Hallier, 298, 299,
Ovary, compound, 272-273 evolution of, 272, 273, 274
Hutchinson, 299, 300
simple, 272
Oxydendrum, 128
Mez, 248, 300 Sachs, 289 Wettstein, 299
338
A TEXTBOOK OF SYSTEMATIC BOTANY
Lupinus, 152, 156
Mutation, causes
Luzula, 199 Lychnis, 120
Myosotis, 140
of,
22
N
Lycium, 138, 139 Lycopersicon, 137 Lysichiton, 200
Names, botanical or
scientific,
M
advantages
of,
221
Mabea, 114 Magnolia, 95, 96 Magnoliaceae, 94-96, 97 Magnoliales, 299 Mahonia, 98 Major characters, 244, 264
authority for, 226, 230w. binary generic, 221
265 stability of, 265 Malaceae, 148 Malvaceae, 104, 106
origin
binomial, 217, 220
disadvantages
of,
222
generic, 219
nonvalid, 222-225
and nature, 219 rejection of, 223-225
clear-cut,
specific,
phylogenetic conceptions
of,
225
256 common, 30, 217 varietal,
authority
for, 218,
219
origin of, 217
standardized, 219
synonyms for, 219 value of, 218 weaknesses of, 218 family, 250 generic, 219 ordinal, 250 of,
248
Mimosa, 153 Mimulus, 140, 141 Minor characters, 265, 266 Modification, definition
220
valid, 222, 227, 229 validity vs. legitimacy of,
Manihot, 114 Manuals, 31, 316-318 revision of, need for, 303 Marrubium, 145 Mathiola, 119 Medicago, 152, 154 Melanthacea< 196 Mentha, 145 Menzieaia, 130 Mertensia, 140 Metonyms, 223 Mez, Carl, 247
specific,
varietal,
220 256
Nelumbium, 103 Nepeta, 145
264
Nicotiana, 137
Monocotyledons, 76 characters of, 195 families of, 194-216 origin of, 194
Nodules, 152
relation of, to dicotyledons, 76
Monophyletic origin, Monotropa, 128, 130 Monotropaceae, 128 Monstera, 200
219-
226
74, 77, 194,
303
Morphological discoveries, 287 Morphological indicators, of phylogeny, 243, 276-280 difficulties in applying, 244
Nomenclature, binomial system 217, 220, 284 definition of, 4 digest of rules for, 234-236 effects of rules for, 236
of,
preceded taxonomy, 281 relation of
taxonomy
to, 1,
217
type-basis code for, 232
Nomina
conservanda, 229, 230, 234,
236
Notebook, field, 54 Nuphar, 103
INDEX Nuts, Anacardiaceae, 171 Betulaceae, 181 Drupaceae, 151 Fagaceae, 176 Juglandaceae, 174 Nymphaea, 103 vascular bundles in, 195 Nymphaeaceae, 102, 103, 104 Nyssa, 183
339
Oxyria, 124 Oxytropis, 150
Paeonia, 99, 102 Paleobotany, 241, 246, 326, 327 contribution of, to taxonomy, 259 relation of systematic
botany
to,
6
O
Paleontological records, 12, 13, 246-
247 Paleontology, 24, 247
Odontites, 141
Oenothera, 160 Oil, 105, 111, 114, 132,
Palmaceae, 202 Panicum, 206
145
Olea, 132
Papaver, 116, 117
Oleaceae, 132
Papaveraceae, 116, 117 Papilionaceae, 151
Onagraceae, 159, 160 Ontogeny, 15 Opuntia, 163, 164 Orchidaceae, 212-215 comparison of, with Compositae, 215 Orders, of gymnosperms, 77-84, 89 Origin, of angiosperms, 13, 91 of binomial system, 220
78
(See also frontispiece) of
of
homonyms, 225 hyponyms, 225
ity,
227
Parthenocissus, 165
Paspalum, 206
Pelargonium, 108, 109 Pentstemon, 140 Peperomia, vascular bundles in, 195 Perianth, taxonomic value of, 274
184
Phaseolus, 152, 153
Philadelphus, 157
300
typonyms, 223 Orobanchaceae, 142, 148, 144 Orobanche, 143, 144 Oryza, 205 Osmorhiza, 187 Ovary, compound, 272-273 evolution of, 272, 273, 274 simple, 272 Oxydendrum, 128
Parentheses, in designating author-
Petunia, 139
of monocotyledons, 194
of
Paratypes, 233
Petroselinum,
of land flora, 326 of metonyms, 223
polyphyletic, 74, 77, 194, of synonyms, 222
213 Parasitism, 27, 142, 277
Pastinaca, 184, 185 Pedicularis, 141
names, 219 of cotyledons, 194 of cultivated plants, 322
of botanical
of dicotyledons, 91 of gymnosperms, 13, 77,
Parasitic plants, 75, 140, 142, 167,
Phleum, 205 Phoenix, 202 Phoradendron, 167, 168 Phylogenetic conceptions, of Bessey,
293-296 Eichler, 290,
300
Engler, 291, 292, 300 Hallier, 298, 299,
300
Hutchinson, 299, 300 Mez, 248, 300 Sachs, 289
Wettstein, 299
A TEXTBOOK OF SYSTEMATIC BOTANY
340
Phylogeny, 15 as the basjsrfor taxonomy, 8 embryological evidence of, 14 morphological and antomical evidence of, 11, 14 morphological indicators 280
of,
276-
Pomaceae, 148, 149 Populus, 125-127 Potentilla, 146, 147 Press for plants, 48, 49
Pressing plants, 48-49 Primitive structures, 272, 278, 279 Priority, in establishing names, 227,
of spermatophytes, 77, 91, 194
235
ontogeny, 15 Physalis, 137 Ptcea, 84 Pimpinella, 186
in
vs.
starting point for, 230n. Progressive development, 25, 277 Prot angiosperms, 92 ' '
Pinaceae, 84r-86
Pinus, 84
Pisum, 152 Planera, 106 Plant breeding, use of systematic botany in, 5 cultivated
and economic,
322, 323
Publication,
306
media
for taxonomic,
305, 306 of
names, 225, 306
Purshia, 147 Pyrolaceae, 128
Pyrus, 148
in technical terms, 38 of,
Ptelea, 111 of names, 225,
Pulsatilla, 102
descriptions of, 37 in common terms, 38
portrayal
' '
Prunus, 149, 160, 151 Pseudotsuga, 84
Pistachia, 171
Plants,
nomenclatural
establishing types, 231
37
by floral chart, 40, 42, 43 by floral diagrams, 38, 39 by illustrations, 38 by symbols and formulae, 40,
Quevws, 175-177, 178 41
Poo, 205
Poaceae, 205 Podophyllum, vascular bundles in, 195 Poisonous plants, Anacardiaceae, 171 Araceae, 201 fcclepiadaceac, 134
Hmpositae, 192 Brupaceae, 151 Ericaceae, 130 Euphorbiaceae, 115 Leguminosae, 156 Ranunculaceae, 102 Solanaceae, 139 Umbelliferae, 187 Pollen grains, 275
tt
Races, biological, 258 Radicula, 119 Rariales, 92, 94,
299
Range management, tematic botany
in,
use 5
of
sys-
Ranunculaceae, 99, 100, 101, 102 Ranunculus, 99, 102 Raphanus, 119 Raphia, 202
Ray, John, quotation from, 241 system of, 284 Recapitulation, law of, 15 Regressive development, 26, 27 Relationships, 1 anatomical indicators
of,
245
Polygonaceae, 123, 124, 125
basis of classification of, 8, 9, 10
Polygonum, 125
diagram
of,
238
INDEX Relationships, morphological indicaof,
indicators
physiological
246 of,
Saprophytism, 27 as an expression of evolution, 280 as a form of degeneracy, 27
tors of, 243
paleobotany, evidence
341
245,
247
origin of, 277 Sarcobatus, 121, 122
Reproductive structures, taxonomic value of, 265 Rheum, 124
Saxifraga, 167
Rhipsalis, 163
Stir pus, 203
Rhizobium, 152 Rhododendron, 128, 130 Rhus, 171 Ribes, 158, 159 Ricinus, 113 Robinia, 152 Roots, 5 taxonomic value of, 270 terms pertaining to, 56 (See also uuder each family)
Scopulophila, 121
Rosa, 146
Sida, 104
Rosaceae, 145, 146, 147 Rubia, 187 Rubiaceae, 187 Rubus, 146, 147 Rules of botanical nomenclature, 234-236, 312-314 effects of, 236 Rumex, 124, 125 Rutaceae, 111, 112
Sieversia,
Saccharum, 205 Julius of,
von,
classification
289
Kagina, 121 Sagittaria, 196 Salicacoae, 125-127 Salicornia, 122 Salix,
names, 219
Scrophulariaceae, 140, 141, 142 Scutellaria, 145 Seeds, 73
taxonomic value of, 276 terms pertaining to, 73 (See also under each family) Sequoia, 86, 87 Serum diagnosis, 247 Setaria, 210 147
Sisymbrium, 118, 119 Sisynnchium, 211 Smilax, 267 venation, 195, 271 Solanaceae, 137, 138, 139 Solanum, 137, 138, 139 Kolidago, 189, 192
Sonchus, 193 Sorbus, 148 in,
282
Species, elementary or primary,
252
Southern Europe, taxonomy Specialists, work of, 43 Specialization, 25
Sabal, 202
system
Scientific
SorQhurn, 210
S
Sachs,
Saxifragaceae, 157, 158
125-127
Salsola, 121, 122
Salvia, 145
Sambucus, 188 Sanguinaria, 116
Sapium, 114 Saponaria, 120, 121 Saprophytic plants, 75, 213
Linnaean or Gray an, 252 newer concept of, 253-255 number of names, 222 n. splitting of, 252 subdivisions of, 253 unit of classification, 251
Specimens, discoloration field data for, 53, 54 heat for drying of, 50 labeling of, 51, 53 molding of, 52 of,
51
preservation
of,
mounting
47
of,
49
A TEXTBOOK OF SYSTEMATIC BOTANY
342
Specimens, securing of, 31 selection of, 47 storage of, 52 Spergula, 120 Spermatophyta, 75 characters of, 269-276 families of, 77-215 general features of, 74 origin of, 74, 77 phylogeny of, 77, 91, 194 Spinacia, 123 Spiraea, 146, 147
an indicator
Stability, as
Systems of taxonomy, son, 299 of de Jussieu, 286
of Sachs, 289 of Wettstein, 299 (See also
274
Taxonomic
publications,
media
for,
Taxonomic systems, 281-304, 314316 9 comparison of Engler's and Betsey's, 296 competition of, 300-302 evolutionary, 288 influence of Darwin on, 288 pre-evolutionary, 281 rigid, 241 usage, difference in, 301 artificial,
of, 270 terms pertaining to, 56, 57 (See also under each family) Stipa, 210 Strains, biological, 258 Strobilus, 74, 76, 92, 272
Suaeda, 122 Sugar, 123, 171, 210 Symbols and formulae, 40, 41 Symphoricarpos, 188
(See also
Systematic botany, 305-330
literature
of,
methods of teaching, 2-3 of, in
botanical studies,
purposes of, 4 uses of, 5-7 value of, 1, 4
Systems of taxonomy, 281-304 of Bentham and Hooker, 288 of Bessey, 292 of de Candolle, 286 of Eichler, 289 of Endlicher, 287
and Prandtl, 291 298
Systems of taxonomy) of, 242, 276-280
Taxonomy, bases
Symplocarpus, 200 Synonyms, 222-225 Syringa, 132
of Engler
Taraxacum, 189 Taxodiaceae, 86-88
305-306
Starch grains, 277 SteUaria, 121 Stems, 56 taxonomic value
of Hallier,
Taxonomic systems)
Taxodium, 86, 87 of,
Stapelia, 133
place
Hutchin-
of Linnaeus, 285 of Ray, 284
of relation-
ship, 265 Stamens, taxonomic value terms pertaining to, 69
of
1
began with Greeks, 281 categories used in, 249 characters used in, 264-276 chemical indicators of, 247 contributions to, 259-261 controversies in, 242, 300 definition of, 4 development of, 281-300 evolution in relation to, 8
experimental method in, 262-264 general terms used in, 255 of higher groups, 255 logical procedure in, 239 phylogenetic evidences, 242 plan
of,
249
relation of, to nomenclature, 217 (See also Taxonomic systems)
Terminology of buds, 58 flowers, 65-71
INDEX Terminology of
fruits,
inflorescences,
71-73
and isolation, 23 mechanism of, 21
Variation,
63-65
leaves, 58-63 roots, 56 seeds,
343
natural, 20
and natural selection, 19 troublesome, 36
72
specialized stems, 57
Varieties,
stems, 56-57
256
horticultural
Thalictrum, 99, 100, 195, 206
and
Theophrastus, 282 .Ttdaspi, 119
Vestigial structures, 15, 16, 27
Thuja, 88, 89 Thym#9, 145
Vicia, 152, 163 Victoria regia, 103
Torrey, John, 1
Viola, 115, 116
Trifolium, 152, 153
Violaceae, 115, 116
Trillium, venation, 195
Vitaceae, 165
IVowel, 47 Triplaris, 125
Vtiis, 165,
166
W
Triticum, 205
Tsuga, 84 Tulipa, 196
Wallace, A. R., 18
Turesson, Gote, 262, 263, 310 Type-basis code of botanical nomenclature, 232,
313
concept, 231 included in rules, 234
value
of,
232
specimens, classification preservation of, 53
'i' pe
Types, comparison of terms
Weeds, Asclepiadaceae, 135 Chenopodiaceae, 123 Compositae, 193 Convolvulaceae, 137 Cruciferae, 119
Type ,
agricultural,
Vasculum, 8 Verbascum, 140
of,
232
for, 231,
232 morphological, 231 nomenclatural, 231 acrological, 231
Gramineae, 210 Leguminosae, 157 Polygonaceae, 125 Solanaceae, 139 Welwtschia, 89 Wettstein, R., 299, 315
Typonyms, 223
U
Xanthium, 189, 191, 192
Y
Ulmaceae, 106, 107, 108 Ulmus, 106, 107 (Jmbelliferae, 184 Uniformity, efforts toward, 228 Uniting groups, 226
Yucca, 196, 206
Z Zamia, 81
Vacciniaceae, 128
Vaccinium, 128 Valid names, 222, 226, 228
how
derived, 226, 228
Zantedeschia, 196 Zanthoxylum, 111 Zea, 205
Zygadenus, 198, 199 Zygocactus, 163
258