Chemical Plant Taxonomy

540 Pages·1963·7.831 MB·English

by  T. Swain (Eds.)

Chemical Plant
Taxonomy
Edited by
Τ. SWAIN
Low Temperature Research Station Cambridge, England
}
1963
Academic Press · London and New York
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U.S. Edition published by
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Copyright © 1963 by ACADEMIC PRESS INC. (LONDON) LTD.
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Library of Congress Catalog Card Number: 63-14494
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List of Contributors
E. C. BATE-SMITH, LOW Temperature Research Station, Downing Street,
Cambridge, England (p. 127)
A. J. BIRCH, Department of Chemistry, The University, Manchester,
England (p. 141)
G. EGLINTON, Department of Chemistry, The University, Glasgow,
Scotland, (p. 187)
H. ERDTMAN, Institutionen for Organisk Kemi, Kungl. Telcniska Hogs-
kolan, Stockholm 70, Sweden (p. 89)
R. D. GIBBS, Botany Department, McOUl University, Montreal, Canada
(p. 41)
H. FLÜCK, Pharmazeutische Institut, Eidg. Technische Hochschule,
Zürich, Switzerland (p. 167)
R. J. HAMILTON, Medical School, Baylor University, Houston, Texas,
U.S.A. (p. 187)
J. B. HARBORNE, John Innes Institute, Hertford, England (p. 359)
R. HEGNAUER, Farmaceutisch Laboratorium, Hugo de Grootstraat 32,
Leiden, The Netherlands (p. 389)
J. HESLOP-HARRISON, Department of Botany, The University, Bir­
mingham, England (p. 17)
A. KJJER, Organic Chemistry Laboratory, Royal Veterinary and Agri­
cultural College, 15 Bulowvej, Copenhagen, Denmark (p. 453)
R. PARIS, Faculte de Pharmacie, 4 Avenue de VObservatoire, Paris 6,
France (p. 337)
V. PLOUVIER, Laboratoire de Chimie, Museum National d'Histoire
Naturelle, 63 Rue Buff on, Paris 5, France (p. 313)
J. R. PRICE, Division of Organic Chemistry, Chemical Research Labora­
tories, C.S.I.R.O., P.O. Box 4331, G.P.O., Melbourne, Victoria,
Australia (p. 429)
F. B. SHORLAND, Fats Research Laboratory, D.S.I.R., P.O. Box 8021,
Wellington, New Zealand (p. 253)
N. A. S0RENSEN, Institut for Organisk Kjemi, Norges Tekniske Hogskole,
Trondheim, Norway (p. 219)
S. M. WALTERS, Botany School, Downing Street, Cambridge, England
(p. υ
ν
Preface
Systems of classification do not necessarily embody implications of
relationship in their structure, but in fact, all those concerned with
plants do employ such concepts to the greatest possible extent com­
patible with existing knowledge and practical utility. The ultimate
natural system would be one based on an infallible knowledge of the
genealogy, from one ancestral type, of every member included in it
and, despite the impossibility of deriving such knowledge, this is the
ideal towards which the more natural systems pretend. In this context,
chemistry may have more to contribute than any morphological analy­
sis, not only because of the relative evanescence of most plant tissues
in geological deposits, but because the biochemistry of evolutionary
processes can be deduced from existing forms.
Chemical plant taxonomy, then, although a very convenient desig­
nation for the activities which it encompasses, must not be taken to
indicate that it is an attempt to classify plants solely on the basis of
their chemical constituents. In fact its application has up to now
usually added confirmatory evidence to agreed plant classification
based on exomorphic and other characters. The use of chemical criteria,
however, adds a powerful weapon to the armoury of the taxonomist.
When properly applied it is undoubtedly more useful than much sub­
jective morphology (e.g. leaf shape) although no more so than objective
observations such as the numbers of a given organ. However, whereas
the latter is but one parameter or "bit" of information, the total
number of individual chemical compounds (including proteins and
other polymers) which such an organ can contain may run into hun­
dreds, each of which might be useful in the total description of the plant
in question. Many of these compounds are so common that they have a
small taxonomic value, but others, notably the so-called secondary
plant products, are often restricted to certain taxa and may help to
distinguish one group of plants from another. Often the variation in dis­
tribution can sharpen distinctions in indeterminate taxa, and may also
disclose hitherto unsuspected relationships.
The vast explosion in the exploration of the distribution of natural
products over the last 10 years is a result in part of a growing interest
on the part of botanists in the chemistry and biochemistry of plants,
vii
viii PREFACE
but more especially of the development of new analytical techniques
in organic chemistry such as chromatography and ultra-violet, infra­
red, nuclear magnetic resonance, and mass-spectroscopy. With the help
of such methods a large number of individual compounds from any one
plant can be identified unambiguously in a very short space of time.
The application of chemistry not only helps the taxonomist: the
knowledge gained also stimulates the interest of the chemist and bio­
chemist interested in biosynthetic processes. The occurrence of a given
compound in one species and one of its congeners in a nearly related
species often yields evidence of steps in biosynthesis which have pre­
viously been unsuspected.
This book is the first comprehensive attempt to survey the scope and
usefulness of chemical plant taxonomy. Its form was determined by a
Symposium held in Paris in October 1962 supported by The North
Atlantic Treaty Organization. A perusal of any of the chapters will show
that we are but at the beginning; that so much more needs to be done.
The reasons for this are clear. With few exceptions those interested in
chemical plant taxonomy are restricted either in their botanical or
chemical field of activity. It is a formidable task to put together the
whole of plant taxonomy and plant chemistry and emerge with an
ultimate generalization. Nevertheless it is hoped that this volume
will lay a secure foundation on which to build, or at any rate, begin
to build a bridge between the two disciplines.
As Editor, I can only say how grateful I am to all the expert con­
tributors who have so extensively displayed their knowledge of the
subject, and especially to Dr. E. C. Bate-Smith, Prof. H. Erdtman and
Prof. R. Hegnauer, whose work has stimulated so many others and to
whom any praise for the usefulness of this book is due. Chapters 11,
12 and 14 are translations; they were originally submitted in French
(11, 12) and German (14). I would also like to thank the staff of
Academic Press for their valued co-operation.
T. SWAIN
April 1963
CHAPTER 1
Methods of Classical Plant Taxonomy
S. M. WALTERS
Botany School, University of Cambridge, England
CONTENTS
I. Introduction . . . . . . . . .. 1
II. Folk Taxonomy . . . . . . . .. 1
III. Linnaean and Post-Linnaean Taxonomy . . . .. 4
IV. Darwin and "Evolutionary Taxonomy " . . . .. 6
V. Relationship . . . . . . . . .. 7
VI. The Practice of Taxonomy . . . . . . .. 8
VII. Developments in Taxonomic Practice . . . . . . 10
VIII. Taxonomy of Lower Plants . . . . . . . 12
IX. ''Omega-taxonomy" . . . . . . . .. 14
References . . . . . . . . .. 14
I. Introduction
It is difficult to give an adequate account of the methods of classical
plant taxonomy in a limited space without neglecting certain fields which
might legitimately be included under this title. Nor would it be particu­
larly useful to dwell either on the factual historical background, which is
in any case richly documented in botanical libraries, or on the details of
the traditional taxonomist's procedure, which might be tedious and
would certainly be difficult to illustrate. This chapter is therefore mainly
concerned with the general practice of plant taxonomy, and with the
historical background in so far as it is essential to explain that practice.
Since, however, it is not possible to understand the methods of tax­
onomy without reference to principles or to the philosophical and
general scientific background, I have thought it necessary to include
such topics where appropriate.
II. Folk Taxonomy
Most text-books of plant taxonomy include a historical survey, which
almost invariably begins with the botanical writings of the ancient
ι ι
2 S. Μ. WALTERS
Greeks, especially Theophrastus and Dioscorides. Although such a start­
ing-point is logical enough, for it is these classical writings which pro­
vided the basis for the mediaeval Herbals of Europe, it should be stressed
that plant taxonomy, concerned with the recognition, naming, and
classification of different kinds of plants, is an ancient and basic human
activity arising from the very practical studies of food and medicine.
Students of linguistics and anthropology have provided fascinating
examples of hierarchical plant taxonomies in the languages of primitive
tribes. As an example I could take the case recently published by Conklin
(1962) from the language of the Hanunoo tribe in the Philippines
(Table I). In this example note, firstly, that the language provides the
expected distinctions of "plant" (v. "animal") and "herb" (v. "woody
plant"); secondly, that at approximately the level which we recognize
as generic, there is the equivalent of a genus name "ladaq" (Capsicum);
thirdly, that this element ("lada") operates as a generic name in the
remaining classification; and, lastly, that the classification of what we
would call "cultivars" of the Chilli pepper, Capsicum annuum L., is im­
pressively detailed.
This example (and no doubt many others could be worked out) illumi­
nates the background of our modern taxonomy in a way which seems to
me both important and neglected. The taxonomy is called forth by the
demands of practical situations. Words exist in the language to communi­
cate gross distinctions between plant and animal, obvious distinctions
between peppers and other kinds of plant, and quite subtle distinctions
between agricultural "cultivars" of peppers. No clear line can be drawn
between the act of naming and the act of classification, since every name
implies a recognition of at least two groups (e.g. "peppers" v. "other
plants"). The hierarchy of names arises as a response to the needs to
distinguish more or less precisely for different purposes. Presumably all
cultivated peppers need certain agricultural treatments; for such con­
versations "läda balaynun" would suffice. When the relative merits of
two crops are discussed, however, "cultivar names" are needed.
We should note two further points in this linguistic situation. Firstly,
no explicit definitions of the terms are necessary for effective communi­
cation. Indeed, if we think about it, we all know that this is so in our
everyday use of language—and if we doubt it, a moment's reflection will
soon convince us of the truth. Definitions of terms become necessary in
situations such as legal disputes (where, as in a recent English court case,
success or failure turned on whether Boletus edulis "is" or "is not" a
"mushroom"), or in situations where it becomes apparent that lack of
implicit agreement on "what we are talking about" is vitiating an argu­
ment. It is tempting to pursue the implications for taxonomy of this
Ο b Ο Q > ο ο 05
n-
u
duk L.)
n
läda tiritigbayaq (Capsicum frutescens
b.t. äbaq
l.ar
q
m
a
n
tagnä l.b.t. atuktuk
p
n
u
n
TABLE I Hanunoo plant taxonomy (Conklin, 1962) käyuh (Plant) qilamnun (Herbaceous plant) lädaq (Capsicum) (Capsicun annuum L., chilli pepper) hilli pepper) läda balay l.b.m. l.b.t. l.b.t. l.b.m. tähud-mail-pasltih qütin-manuk punkuk kutiq (Cockspur houseyard chilli pepper)
c
n d
u r
da balayn Houseya l.b.m. pinasyak
ä (
l
at
mahär l.b.m. pasltih
n
u
n
a balay l.b.m. h-apun
d
ä
l
m. nis
l.b.batü
4 S. Μ. WALTERS
view of language which has been developed in recent years (cf. Bam-
brough, 1961), but it lies outside the scope of this chapter. I must be
content to emphasize that the definition of most common flowering plant
genera, undertaken by Linnaeus, is similarly preceded by a long history
of the use of these names.
The second point, of particular interest to chemical plant taxonomy,
I feel, is that this primitive folk taxonomy cannot be said to be narrowly
morphologically based. Indeed, it could be argued that it was a regret­
table necessity which in the history of plant taxonomy forced us to base
our modern classification on morphological characters. The importance
of form arises from the impracticability of communicating through the
written word or through illustration the description of different kinds of
plants in anything other than visual terms. We stress morphology in
plant taxonomy because our predecessors found it the easiest way to
write and illustrate, and because by the time of Linnaeus we were so
committed to it that any other way never occurred to us. I shall return
to this point later, after a consideration of the taxonomy of lower plants.
I have spent what may seem to be a disproportionately long time on
this single example, because I believe that it reveals to us the essential
but often overlooked basis of all our taxonomic work. Classification of
kinds of organisms, like all classifications, was and is a severely practical
activity, and if we forget this, we find ourselves bogged down in sterile
arguments.
III. Linnaean and Post-Linnaean Taxonomy
Bearing this in mind, let us look at the work of Linnaeus, who more
than any other single figure made the framework of the "classical"
plant taxonomy just over two centuries ago. It is tempting to think of
Linnaeus as bringing order out of chaos; but it would be equally valid
to stress that Linnaeus was no free agent, devising de novo an ideal system
of classification and an ideal taxonomic procedure. On the contrary, he
was severely limited (as it now appears to us) firstly by the existing classi­
fications and nomenclature, which represented already a considerable
body of work with a long history of its own; secondly by the selection of
material on which that classification was based, which was mainly the
higher plants of Europe; and thirdly by the philosophical and religious
ideas of his time, which led him to formalize a system of genera and species
derived from Aristotelian logic, and justified in terms of special creation.
Note that Linnaeus and all his "classical" predecessors from Theo-
phrastus onwards were self-consciously making classifications, but paid
relatively little attention to the question, "What is the classification for?".
1. METHODS OF CLASSICAL PLANT TAXONOMY 5
Of course, the requirements of classical and mediaeval medicine in par­
ticular provided an easy justification for their taxonomic activity; and
it is easy to see, in the shape of Angiosperm classifications which we are
still using, that pre-Linnaean taxonomic activity had in many cases been
exceptionally great where it was, for reasons of medicine or food, es­
pecially important. In this way it is, for example, possible to explain
why the genera of Gramineae are on the whole smaller than those of
Cy peraceae, or those of the Umb ellif erae smaller than the Cary ophy llaceae.
The implications of this view of the shape and size of Angiosperm families
and genera I have discussed elsewhere (Walters, 1961, 1962); this is not
the place to enlarge upon them.
Linnaeus' answer to the question, "What is your classification for?",
was simple enough. The classification revealed the Creator's plan, and
the named "kinds" were created as such. This is clearly stated in
"Philosophia Botanica" (1751).
"Species numeramus, quot diversae formae in principio sunt creatae".
"Genus omne est naturalis, in primordia tale creatum".
Both the genus and the species were to Linnaeus "natural", "real",
distinctly created units. The genera he arranged in an artificial "Sexual
System ", making his higher groupings on the criteria of number of sexual
parts in the flower. Both the fixed "binomial" of genus and species, and
the artificial Sexual System, were practically successful. Here was now a
workable system geared to a standard herbarium procedure, with an
agreed terminology to describe morphological variation. On this basis,
Floras were written with keys for identification, and the thousands of
new plants from the newly explored Continents were described and
classified. The herbarium method, the standardized description and
terminology, the binomial, and even the use of Latin as an international
scientific language have all survived intact from Linnaeus' work; only
the "Sexual System" has been superseded by a "natural" system of
Families.
Post-Linnaean taxonomy of the higher plants shows remarkably little
change after the main modern families and genera were defined and des-
scribed by de Jussieu (1789), A. P. de Candolle and others at the end of
the eighteenth century, and in the first half of the nineteenth. It is fasci­
nating to read de Candolle's excellent text-book (1819), and to find how
much of it might be re-printed as a manual for taxonomists in the mid-
twentieth century. He is, for example, quite realistic about the "crea­
tion" of genera. I like in particular his advice, in certain cases "to avoid
useless nomenclatural changes, one should leave the genera as it has been
customary to have them, and indicate divisions as simple sections".