BotanicalJournalofthe LinnranSociely(l9811,82:81-87.
Angiosperm classification and phylogeny :
a criticism
E. J. H. CORNER, F.L.S.
91 Hinton Way, Great Sheyord, Cambridge C B 2 5 AH
Acceptedf o r publication October 1980
This is a criticism ofDahlgren’s recent classification of angiosperms i1980) and his basic diagram of
angiosperm phylogeny. The first is shown to include unnatural orders and super-orders; the second
is accordingly as questionable. Basic factors for phylogenetic taxonomy in the angiosperms are
considered. Leptocauly leads to parallel evolution and specific multiplication. Nomenclatural
artifices for taxonomic equivalence are exposed; the name ‘pseudon’ is suggested for a conjectural
taxon.
- classification - nomenclature - parallel evolution - phylogeny
KEY WORDS :-angiosperms
CONTENTS
Introduction .
Dissatisfaction.
Living tibre . .
Criticism . .
References . .
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87
I NTRODUCTI0N
Despite many contributions to this subject, the fact remains, and needs continual emphasis, that the whole history of the angiosperms is still a mystery. Where,
when and in what manner they arose is not known. How they became trees and
took over from the flowerless and fruitless forests is not known; or how they
became grasses, mangroves, palms, aquatic, epiphytic, or climbers. By what series
of improvements their early races were superseded until the modern multitude of
dominant, subdominant, receding and over-specializing genera in geographical
partition was attained is not known. The fossil record has not supplied answers.
Exponents, therefore, must rely on inferences and deductions made from the
comparison of the living. This evidence has become so manifold and immense
that no one can be expert, except in a small part. Much of the evidence, too, is
derived from sampling and it is difficult to assess the validity of generalities
81
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Q 198 1 The Linnean Society of London
a2
E. J. H. CORNER
derived this way, especially if they lie outside one’s immediate cognisance; on
repetition they are apt to seem proven. Therefore phylogenies, and the classifications on which they are based, are partly factual and partly inferential. The critic
is uncertain because the source of evidence is seldom given explicitly; and two
other, almost imperceptibly insidious, trends add bewilderment. Phylogenies are
becoming abstract as they are based on the diagnostic differences, or abstractions, which systematists prefer to the multiplicity of real achievement. They are
overwrought and obscured by the artificial code of nomenclature which can
ascribe with learned names ranks which do not exist except in this fantasy and
achievements as fictitious. The whole subject has flowed gradually over the past
century, as glimpses from all branches of botany have illuminated it, into the
confines of taxonomy as the synthetic centre. The admixture of fact, fancy and
abstraction and the continual insertion of new names of no new significance are
withdrawing the subject from general botany and from biology into an academic
pastime. The fog of learning is closing around this beacon of cosmogony.
DISSATISFACTION
Foremost among the abstractions, for instance, there are the features used to
separate, sometimes even to define, dicotyledons and monocotyledons; there is
never an indication of how trees and lianes have sprung from the one and palms
and grasses from the other. As an example that is almost trifling, the prime
distinction between Moraceae and Urticaceae rests on the form of the ovule;
intermediate forms are ignored and genera with intermediate ovules are placed in
one or other family according to other features: yet, figs and bread-fruits are not
among stinging nettles. The fact is that there is not yet a satisfactory classification,
or phylogeny, of Urticales; it would be better to revert to a single family and to
dismiss the order as meaningless, but repetition comes to imply proof and
Moraceae, Urticaceae and Urticales are accepted as fact for phylogeny. Many
large and varied families present the same problem, from palms to Leguminosae;
usually it is only the specialist who is aware of the true facts and he keeps silent.
Concerning the artifices of modern nomenclature, it is necessary to reflect on
the nature of taxa. Individuals make a species; species make a genus; genera
make a family; families make an order: plurality is the factor. There is now
general agreement on the majority of genera and families so that one can speak
with confidence about Ranunculaceae or Orchidaceae, though there will always
be splitters to sever pieces. Much difficulty and uncertainty enters, however, in the
attempt to put families, as taxa of high abstraction, into orders of yet higher
abstraction because parallel (or convergent) evolution, so rife among
angiosperms, commonly renders impossible, with present knowledge, the
distinction between genetic agreement and superficial resemblance. Thus
modern classifications differ mainly in this ordinal arrangement.
One species, however, does not constitute a genus, one genus a family, or one
family an order because they are isolated units with no congeners to constitute
the higher rank. International nomenclature intervenes by demanding in the first
place a binomial; every species must have a generic name. This nomenclature
continues with standard s u f i e s and permits the invention of families, orders and
super-orders, even classes, based on a single species, a single genus, a single
ANGIOSPERM CLASSIFICATION A N D PHYLOGENY
83
family and so on. One species of tree becomes Eucommia ulmoides and this fictitious genus gives rise to Eucommiaceae and the order Eucommiales equivalent,
apparently, with Solanum, Solanaceae and Solanales. A word is needed, such as
‘pseudon’ or ‘pseudotaxon’, to indicate these supererogatory taxa, although in
plain English one would say fudge. The entanglement spreads. Angiosperrnae
become Magnoliopsida, dicotyledons Magnoliidae and monocotyledons Liliidae,
to no advantage but to the obfuscation of previous science. Such names may be
advantageous when a particular point is presented but they are pedantic in the
forum of botany.
LIVING FIBRE
Dissatisfaction with this skeletal phylogeny has brought many efforts to restore
living fibre. For monocotyledons there are theories of geophily, hygrophily,
xerophily and caulescence to explain the evolution of herbs from desert, marsh,
or aquatic habitat into forest vegetation, always with the assumption that palms,
pandans, bamboos and dracaenas are the caulescent terminals of liliaceous progression. For dicotyledons, with much greater diversity, the task has not been
easy. Life-forms have been arranged in various ecological progressions vaguely
rising to the tree which, tacitly, becomes a parallel in the majority of families,
although the wood of tree-families is used for phylogenetic sequence. There is
that extolled by Hutchinson ( 1959) which distinguishes a woody arborescent
stock from a persistently herbaceous. It has support even in recent ideas on
Magnoliiflorae, but it encounters many difficulties by way of intermediates and of
families both herbaceous and arborescent although certainly monophyletic.
Clarification has come in large measure from the biochemical research of BateSmith (1954, 19571, but insufficient analysis of tropical tree-forms has caused
misunderstanding. For my part, brought up under the contrasting influence of
Hutchinson and Engler, and groping in the reality of tropical forest, I was led to
the concept of the megaphyllous pachycaul, or cycad-form, as the primitive
growth-form of the angiosperm from which tree and herb, climber, palm,
bamboo, grass and water-lily had been derived.
This idea, published 30 years ago as the durian theory (Corner, 1949), was a
flash in the pan and quickly forgotten because of that unfamiliarity with tropical
growth-forms in the circle of academic phylogenists. The hiatus has been filled by
the eminent research of Hall6 & Oldeman ( 1970)and the pachycaul is no longer a
freak of tropical ebullition. The durian theory was expanded in my L f e o j Plants
(Corner, 1964)into the rise of angiosperm forest. It was exemplified for monocotyledons in my Natural Histo?y o f P a l m (Corner, 1966). I t was explained in detail
for the genus Ficus (Corner, 1978, with a full list of references). Finally it was
summarized for dicotyledons in more general classificatory form in my work on
seed-structure (Corner, 1976). Ficus was chosen as a genus to exemplify what
could be learned from the living. As a large and unquestionably monophyletic
genus, it displayed typical angiosperm diversity and success. What it disclosed in
the passage from pachycauly to leptocauly could be read in many other, if not all,
big and monophyletic genera of dicotyledonous families. I concluded that what
phylogenies lacked was appreciation of the pachycaul. As all major genera, so all
major families stem from this ancestry. Comparison of these taxa in their leptocaul states, where parallel evolution has played such a deceptive part and which
have supplied the material for phylogenies, had confounded the issue.
84
E. J. H. CORNER
I t has confounded the issue from Linnaean beginnings. The main trend in the
history of angiosperm systematics has been the detection of parallelism, or convergence; grades, assembled taxonomically on this similarity, have been resolved
into phyletic lines which cut across them. From numbers of stamens and styles,
dioecism and monoecism, through grades of sympetaly, apetaly, perigyny,
epigyny, zygomorphy, microspermy and so on, modern phyletic units have been
disengaged into fairly homogeneous families. The grouping of these into orders
is still confused by reliance on floral construction with its pervading leptocaui
parallelism. This grouping calls for another means, as pointed out in my work on
seeds, and titles with the s u f k ‘-ales’ must be suspect. If RaffEesia or Piper can be
derived from Magnolia, then why not from Cactus or Rosa?
I have attempted to answer criticisms of the durian theory (Corner, 1953,
1954a, b, 1976).Although it is widely disregarded, I am not aware of refutation. I
still ask of angiosperm phylogenists, therefore, the question that I sought to
answer, such as whether the primitive angiosperm was herb or tree, tropical or
extra-tropical, with simple or compound and acropetal or basipetal leaf, evergreen or deciduous, with small or large and terminal or lateral flower, with small
or large and dehiscent or indehiscent fruit, with small or large and arillate or
exarillate seed and whether the seed was first incorporated into a fruit or a flower.
The last point is vital. If the fruit, as seems obvious to me, then the true concept is
that of Angiospermae (-aphyta, -atopsida) rather than Magnoliopsida and Magnoliiflorae which, based on the flower, must have been subsequent to the original
angiosperm. Fruit and seed figure so little in phylogenies that one might conclude that the characteristic manner of angiosperm reproduction was immaterial.
In truth, they are the missing means of ordinal classification. Preference for the
flower, which is easier to investigate and to describe, has led to many investigations into the manner of pollination of species in what are deemed to be primitive
families, with primitive effect so far as can be judged from modern insects and
breezes, but little interest has been shown in the much older methods of seeddispersal.
CRITICISM
A recent article by Dahlgren ( 1980)on angiosperm classification and phylogeny
has raised all these matters again because he seems assiduously to have avoided
all the problems that I have emphasized. Thus negatived, I can derive no idea
from his account of what he supposes that the primitive angiosperm might have
been in growth-form, leaf, flower, fruit and seed, apart from what has been long
accepted, that the primitive seed was perispermous. He deals mainly with plants
in leptocaul parallelism; pachycaul is not mentioned, or megaphyily and seed
and fruit scarcely enter. Angiosperms become at once Magnoliopsida in order to
render them “equivalent to the main groups of the gymnosperms (Pinopsida,
Ginkgoopsida, Cycadopsida, Gnetopsida)”. Why this equivalence should be
needed or how it can be justified is not explained. In numbers of species, genera
and families and in structural, functional, reproductive and ecological achievement, angiosperms vastly exceed all gymnosperms. Only an absurd artifice of
nomenclature could debase them. Ginkgoopsida is, of course, a pseudon
ANGIOSPERM CLASSIFICATION A N D PHYLOGENY
85
comparable with Eucommia. Similarly, as families or orders of Gnetopsida are
pseudons, so this idealization of equivalence is false. We are, then, introduced to
super-orders, suggestive of super-super-orders or super 2-orders, as another act
of supererogation when the orders themselves are suspect. Super-orders
terminate in ‘-florae’. When the importance of fruit and seed is realized, perhaps
super 2-orders will terminate in ‘-fructae’, and super 3-orders in ‘-seminae’.
Ovary and ovule are embryonic structures adapted to the flower as the precocious fruit-bud; what they will become cannot be predicted except by analogy
from observed cases. It is worth recalling the five enigmas of the flowering plant.
Given a plant in the vegetative state, its flower or inflorescence cannot be
predicted without previous knowledge. Given the flower, its fruit cannot be predicted without previous knowledge. Likewise, from the fruit the seed cannot be
predicted, or from the seed the seedling, or from the seedling the adult plantform. A realistic phylogeny, and classification, should co-ordinate these five
categories of habit (leaf), flower, fruit, seed and seedling. A classification which
disregards this and opens with ‘-florae’ begins in the middle of angiosperm
evolution and deals inevitably with grades of parallel achievement. I t is what the
opening super-order Magnoliiflorae displays.
As I have shown (Corner, 19761, the families usually assigned to Magnoliiflorae
have some nine different kinds of seed-structure, many of which can be traced
into more advanced families assigned by floral grades to other super-orders.
Dahlgren remarks that he has put these distinctions of seed into one of his
unpublished diagrams and then drops the subject. They must, presumably, have
destroyed the verisimilitude. To the seed-distinctions those of fruit should be
added and, although the fruits are yet imperfectly described, they reinforce the
conclusion that the Magnoliiflorae represents a grade of parallel attainment in
flower and leaf. The super-order consists not of primitive families but of modern
families descended from angiosperms in which the primitive flower had become
established.
Diagrams are certainly desirable when offering a point of view, especially over
a scene so complex as the angiosperms. The simpler the diagram, the more
quickly the intent may be grasped but, as diagrams are elaborated, their fascination seems to lead the author further from reality. Dahlgren’s basic diagram
represents super-orders budding orders in the manner of a yeast colony; many of
these, of course, are pseudons. Proximity roughly indicates the alliance of superorders and the area of each super-order colony is an indication of the number of
living species that it contains. The colonies are supposed to represent the crosssection of the branches of a phylogenetic tree, but this branching is too mycological for conviction and there is no trunk. What the number of species is meant
to signify is not clear. I t could be a test of taxonomic zeal, to the advantage of
splitters, or it could indicate the supposed success of a super-order, though this is
by no means obvious. There is that extremely successful palm Nipa which
occupies with massive endurance vast tidal areas of lands bordering the Indian
and west Pacific oceans: yet it seems in its long geological history always to have
been a monotypic genus. Its success vastly exceeds that of Eucommia though they
would be given the same area in the diagram if a splitter made a family and an
order for this exceptional palm. In contrast, genera of slender palms of minor
ecology multiply into numerous species of restricted habitat. Leptocauly seems to
be one way to specific increase and specialization. Then I think of those two
86
E. J. H. CORNER
species of giant tree which compose the caesalpinioid genus Koompassia; they
almost dominated parts of the lowland Malayan forest before man destroyed so
much. So, a genus of two species vastly outweighs in biomass and ecological effect
not just the big genera of many herbaceous species but even many small families
and orders. One species of Koompassia is not the equivalent of one species of
Bulbophyllum, except as an artifice of nomenclature. Mangrove has few, widely
dispersed and successful species of tree, whereas pandans, joining the mangrove
vegetation, multiply into many species of restricted habitat and distribution. In
Dahlgren’s basic diagram, Urticales is a rather small bulge from Malviflorae; yet
Ficus, but a part of Urticales, holds one of the commonest kinds of tree in the
Asian tropics and has evolved the biggest of living organisms, namely the banyans, How is Ficus benghalensis L. to be equated with Urtica urens L. or Poa annua L.,
except by a trick of nomenclature? Is Eucommia, as a tiny bud (Eucommiales)
from Corniflorae, nascent or decadent from a big genus of many species? The
past history of Eucommia might alter considerably the colony of Corniflorae.
Thus, I find the area-implications of the diagram unsound. To have used the
number of genera would have made this criticism obvious. If the total biomass of
super-orders was known and used for this area-basis, it would completely alter
the picture.
The estimate of affinity between super-orders depends on their content. Many
families and orders seem to me to have been mistakenly associated by Dahlgren,
when I consider leaf, flower, fruit and seed. If the orders are suspect, so are the
super-orders. Thus, both size and arrangement of the colonies as phylogenetic
branches are questionable; nevertheless, the diagram conveys the author’s point
of view.
The content of the first super-order Magnoliiflorae is perplexing. Thrust into
an idea of “mainly woody members of the so-called primitive dicotyledons” and
sandwiched between Annonales and Magnoliales, there are Aristolochiaceae,
Hydnoraceae and Rafflesiaceae. The gynoecium of the super-order is given as
apocarpous or monocarpellate, but it is inferior and, commonly, 4-6 locular in
Aristolochiaceae and more or less inferior in the other two families, even multiplacental in Rafflesiaceae. I t is not clear, moreover, that these three fanJ‘1’ies are
woody or primitive or that they have “cells with essential oils in the leaves”; it is
not clear how the endosperm of Rafflesiaceae can be called cellular when it is
described by others as nuclear. The seeds of this family differ from those of
Annona, Magnolia and Myristica in all diagnostic ways ; those of Aristolochiaceae
have their own peculiarities which are certainly not Annonalean or Magnolialean.
Dahlgren admits that the diagnostic characters (or abstracts) of Magnoliiflorae
may be variously absent from some of the orders which he includes but it is, then,
impossible to know how to diagnose the super-order: he includes Nelumbo. If
such vagaries are admissible, the strangely primitive and apocarpous Archidendron
(Mimosaceae)should have been included and, likewise, all the Leguminosae and
one could add, for example, apocarpous Connaraceae, Dilleniaceae, Rosaceae,
Rutaceae, Simarubaceae and Sterculiaceae. Fundamental fruit and seed are
omitted though the author has endeavoured “to take into account as much
information as possible”.
As a highly questionable concept of monophyletic evolution, Magnoliiflorae
set the example for many other super-orders, e.g. Nymphaeiflorae, Ranunculiflorae, Malviflorae, Violiflorae, Theiflorae, Roseiflorae, Myrtiflorae, Rutiflorae
ANGIOSPERM CLASSIFICATION AND PHYLOGENY
87
and Santaliflorae. Rather than repeat what is discussed as concisely as possible in
my work on dicotyledonous seeds, I refer to its fourth chapter (Corner, 1976:
25-47).
What seems the emptiness of this exposition is the brief notice given for
Leguminosae; styled Fabales, they have the super-order pseudon Fabiflorae. The
legume which distinguishes this enormous alliance is thereby erased and has no
mention. The characteristic seed is accordingly omitted. Parallel similarities with
Rosaceae, Connaraceae and Sapindaceae are repeated as if indicative of monophyletic evolution, to the nullification of constructive thought. The ‘fabiflos’ is
not a prime character of Leguminosae but a peculiarity of Papilionaceae dependent on the gamosepalous calyx. Problematic Swartzioideae have no mention. I
cannot but observe that so many of these families, orders and super-orders are
derived in name from temperate genera, as if one was looking through the wrong
end of the telescope.
With regard to the monocotyledons, or Liliidae, for which we await a modern
treatise on seed-structure, I find some strange bed-fellows. Bamboos are joined
with Flagellaria in Poales and this order is put into the super-order Commeliniflorae, as if Melocanna were a better or worse Eriocaulon, if it is the number of
species which tell. Pandans are joined with palms in the super-order Areciflorae
of which it said “the group consists of large herbs to little branched trees”. The
expression fits neither a thicket of pandans nor a tangle of rattans, which are two
common and devastating obstructions in eastern tropical forests. There is no
reference to my discussion on the primitive pachycaulous nature of palms and
their distinction from pandans (Corner, 1966). N o one knows the origin, affinity,
or evolution of either. To blur this ignorance with such assurance is to lay a
pitfall; and research is not furthered.
The kingdom of angiosperms has led to the kingdoms of civilization. That its
success should be reduced to a masquerade of nomenclatural make-belief, in
equivalence with Ginkgo, is as unacceptable as it is unreal. That is why I prefer the
established names, such as angiosperm, dicotyledon, crucifer, palm, composite,
Gramineae and Leguminosae, for they entail no such fallacy.
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BATE-SMITH, E . C., 1957. Leuco-anthocyanins 3. The nature and systematic distribution of tannins in dicotyledonous plants.Journal ofthe Linnean Society (Botany), 55 :669-705.
CORNER, E. J. H . , 1949. The durian theory or the origin of the modern tree. Annals ofsotany, London, N . S . , 13:
36 7-4 14.
CORNER, E.J. H., 1953,Thedurian theoryextended: 1 , Phytomorphology,?:465-476.
CORNER, E . J . H . , 1954a. The durian theory extended: 2. Phytomorphology, 4: 152-165.
CORNER, E. J . H., 1954b. The durian theory extended: 3. Phytomorphology, 4: 263-274.
CORNER, E. J . H . , 1964. TheLfeofPlants. London: Weidenfeld%Nicolson.
CORNER, E.J. H . , 1966. TheNaturalHistoryofPalms. London: Weidenfeld&Nicolson.
CORNER, E.J . H . , 1976. The SeedsofDicoQledons. Cambridge: Cambridgeuniversity Press.
CORNER, E. J . H., 1978. Ficus dammaropsis and the multibracteate species of Ficus sect. Sycocarpus. Philosophical
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DAHLGREN, R. M. T., 1980. A revised system of classification o f the angiosperms. Botanical Journal o f the
Linnean Sonety, 80: 9 1- 124.
HALLE, F. & OLDEMAN, R. A. A., 1970. Lhrchitecture et la dynamique de croissance des arbres tropicaux. Paris:
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HUTCHINSON, J., 1959. The Families of Flowering Plants. London: Macmillan. 2nd ed. (1959) Oxford:
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