The classification of plants

It is basic to the human mind to classify, to break down the things we see around us and file the images for retrieval later when similarsightsappear. The diversity of nature can be interpreted only by some sort of box-within-box storage system. Thus we see the logic behind the hierarchy of categories produced by the taxonomist, as set out in descending order here. This shows the classification for one of the "pebble plants", with the status and name of each category. Note that for some categories the ending (suffix) is standardized so that one can recognize the rank at a glance. Thus, anything ending in -ales is an Order, and so on.

Opinions differ as to how far these units have a real existence in nature — major or minor branchings in the evolutionary "tree", to give a visual analogy —

Below (8.3): Hybrids break down boundaries between species and pose problems lor the classilier. This is a cross between two Lobivlas, one of them Lobivia silvestrii (6.13).

Below right (8.4): Epicacti are of mixed ancestry, even the genera may be unrecorded. For them a cultivar name is used. Top Deutsche Kaiserin x Conways Giant: Bottom: Unnamed hybrid

and how far they are man-made and for convenience of pigeon-holing only. For finer shades of analysis, extra categories may be interpolated. Thus a subgenus can be divided into Sections and a Section into Series. Below the species level we can have further categories also to express finer and finer shades of difference: subspecies (ssp). varieties (var) and forms (f). In Haworthia limifolia we find a var stolonifera f major: a large-leaved form of the variety forming stolons (long-stalked runners), for example. This is distinguished from the type form, which is H. limifolia var limifolia f limifolia.

Because of the impossibility of exactly defining the units of our classification, botanists gravitate into one of two camps: the "splitters" who favour many, small, finely separated units, and the "lumpers" who prefer fewer, broadly circumscribed units. If either policy were pursued uni formly and in moderation throughout the plant kingdom, there would be nothing to choose between them on logical grounds. Unhappily, we have great inconsistencies, and succulents are among the groups where extreme splitting has been pursued. Whereas a conservative taxonomist accepts Notocactus in a broad sense, radicals split off Brasilicaclus. Eriocaclus and Wigginsia (Malacocarpus) on minor differences of flower, fruit and seed. In professional circles the trend is now towards moderation and amalgamation, but undoing past wrongs often involves further changes of names, as in the case outlined below.

In the present book I have tried to adopt conservative treatments wherever they are available, giving the alternative name or names in brackets where felt necessary. It is peculiarly irritating to a grower to be confronted by such ambig uities: he orders several different names from seedlists and ends up with indistinguishable seedlings, oralternatively meets with the same plant under several different names. Books also are a source of confusion, according to which authority they follow. It is natural to ask: Why are there so many names? And which among them is correct? A full answer would fill many pages: only the principles involved can be summarized here.

A Borzicactus by any other name Changes of name may be taxonomic or nomenclatural: two quite different causes. The former is personal and subjective; the latter is a matter of applying the Code. Taxonomic changes are the outcome of renewed study and, sometimes, extra information: what was once regarded as one unit is now seen to be two or three; what once looked like three separate entities are now seen to be linked by so many intermediates that a merger is called for. Such changes are marked (T) in the example cited below.

Nomenclatural changes result from strict application of the articles of the Codes, for a number of reasons. For instance, the same binomial may have been given twice over to different species. Or one species may have been independently named twice. Either situation would lead to chaos and must be corrected. For instance, in 1973 Lavranos named a new aloe Aloe pulchra Lavr.. overlooking an early use of the same binomial. Although the latter is now universally accepted as a species of Casteria. it invalidates the later use of the same binomial, under the rule of priority. So Lavranos's aloe had to have a new name. A bella was chosen because it preserved the same meaning: "beautiful aloe". Nomenclatural changes are marked (N) in the following example, which includes both types of situation.

An attractive new golden-spined cactus (8.5) was described by Ritter in 1962 as Winteria aure¡spina, the only species of a new genus christened in honour of Mrs. Hildegard Winter, wife of a German nurseryman. Unfortunately Ritter failed to notice that the name Wintera was already in general usage for an unrelated shrub, and the difference in spelling of only one letter would undoubtedly lead to confusion. Hence under the Code the early name Winlera (1784) stands and Winteria Ritt. needed a new name. Two people independently supplied one: Backeberg, putting the finishing touches to his Lexikon, called it Winlerocereus. and Ritter himself amended it to Hilde-wintera. both in 1966. Ritter's article appeared in print four months in advance of Backeberg's book, and therefore his name has priority. In 1974 Buxbaum decided that Hildewintera was indistinguishable from Loxanthocereus. and in 1975, taking a still broader concept of genera. 1 included both in Borzicactus We can summarize this chronology so far

1 Winteria aureispina Ritter, Jan 1962.

2 Hildewintera aureispina (Ritter) Ritter, Jan 1966 (N)

3 Winterocereus aureispinus (Ritter) Backeberg, May 1966 (N)

4 Loxanthocereus aureispinus (Ritter) Buxbaum, Apr 1974 (T)

5 Borzicactus aureispinus (Ritter) Rowley. May 1975 (T)

The double author citation is an optional refinement in which the first name in brackets refers to the original publisher of the species, that following to the publisher of the revised binomial.

Reviewing the above names, 1 and 3 are out, as contrary to the Code, but 2, 4 and 5 are valid and all may be used: they reflect respectively the narrow, middle and broad concept of genera.. The grower must make his own choice, depending on his general attitude and the sources of literature he follows. It will be evident, then, that to answer fully the question: "Which is the right name?" one has to study the evidence and the reason for changes. A taxonomic change is a matter of opinion; a nomenclatural change, if properly handled, will be accepted by future writers of books and monographs, so it is best to swallow the pill even if it means loss of a familiar binomial.

Right (8.5): Borzicactus aureispinus. a handsome cactus ol many names, as is explained in the text. The novel container simulates its natural habitat on rock laces

Below (8.6): Dudleya brittonii from Baja California commemorates two lamous American botanists: W. R Dudley ol Stanford University and N. L Britton ol New York Botanical Gardens

The Families of Succulents

As pointed out in the Foreword, no attempt is made here to describe and key down all 10,000 or so recognized species of succulents. Rather, the interest is confined to higher levels in the classification—the genera and Families—and their positioning in relation to each other and to non-succulent relatives. Ten Families, five of leaf succulents and five of stem succulents, are singled out for separate treatment in Part 2. These contain the bulk of succulents most familiar in cultivation today, although size ranges from about 2,000 species in the three largest down to a mere handful where only a small fraction of the Family is succulent. The remaining, still smaller units, are summarized in Chapters 9, 15 and 21.

With some misgivings I have adopted an artificial breakdown on life form into Leaf, Stem and Caudiciform Succglents, knowing that some Families and genera qualify for inclusion in more than one group. Similarly, the two keys will incur the wrath of the pure in heart because I have omitted certain border-line or rarely encountered succulents whose inclusion would merely complicate the scheme and give maximum prominence to minor elements. The presentation is intended for non-technically minded plantsmen: not for the advanced botanist who will prefer his monographs and floras anyway. It must be emphasized that the only real way of distinguishing plant Families is

by flower and fruit characters; any attempt to do without is a poor compromise. Unfortunately, certain groups of succulents are hardly ever seen in flower in cultivation (Didiereaceae, for instance) — hence the impasse. But do not despair if initial attempts to name unlabelled succulents get nowhere. Familiarity with plants lends a wonderful perceptiveness to the trained eye. Just as we recognize our nearest and dearest amonga crowd of thousands, regardless of dress and hair style. so the persevering cactophile learns to tell a haworthia from an aloe or agave just by the look and feel of the leaf, although a description would be long and complicated. If Part 2 does no more than excite the urge to look closer and inquire further, it will have served some purpose.

Left Echinocactus grusonii ! rear) and Ferocactus acanthodes (front) in a nursery. Below Euphorbia caput-medusae. the

Medusa's Head Spurge', shows by its curious flowers that it is no relative of the cactus.

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