QBARS - v30n3 How Many Classifications

W. R. Philipson, Christchurch, New Zealand

It is often remarked that there are two classifications of rhododendrons. If this is so, it would be interesting to find which was the earliest, and perhaps even which is the best. These questions appear straightforward, but that an answer to them is not easy can be illustrated by a question that was put to me the other day. "Which did I favour", I was asked "the classification of Sleumer or the one of van Hoff?". Now this is a question without meaning, because both these botanists contributed something to the same classification of the genus. This classification is old, with a long history of development, and is certainly far from finality. One cannot freeze a classification - it must grow as knowledge grows - but it will usually rise on the foundations already laid down.
When it is said that there are two classifications, a contrast is being made between the old botanical classification (whose torch has been carried recently by Sleumer and van Hoff) and that set out by The Rhododendron Society in their publication The Species of Rhododendron (Editions 1 & 2). In this work the species are arranged in a number of Series (and sometimes sub-series), and at first sight it shows little trace of the pre-existing and well-established classification. But it will be well to take a closer look at its historical context before coming to any conclusion.
As the active plant collectors in China and the Himalayas sent back material to Britain and especially to Edinburgh, eager botanists and more particularly Professor Isaac Bayley Balfour described many new species. In order to help others, and especially horticulturalists, comprehend this multitude of species, Balfour began grouping them according to their general resemblances. These groups he called Series. Gradually he and his associates placed most known rhododendrons into appropriate Series and eventually these were made generally available in The Species of Rhododendron , the botanical authors of which were Tagg, Hutchinson and Wilson. These botanists were well aware of the existing botanical groupings, but wished to have smaller more practical groups based on finer, if often indefinable, distinctions. That they respected the botanical subdivisions is shown by their Series never transgressing the botanical boundaries. Indeed the existence of the botanical groups is assumed, but never stated. For example, lepidote and non-lepidote major groups are assumed, but are not adopted in arranging the Series.
To my mind the intention of the authors was to present the empirical groups (Series) in as simple a manner as possible. To do this the old hierarchies were deliberately omitted, although the authors firmly believed in them. Wilson especially had used the botanical classification extensively in his writings and had even introduced improvements to it. In a sense, the treatment in The Species of Rhododendron is not a classification but a deliberate absence of classification. This is hardly too sweeping a statement for a treatment that divides a multitude of species into 42 groups of equal rank. The human brain calls for a hierarchical arrangement and this was already present, though it had hardly digested the huge increase in the species that became known about the turn of the century.
However this may be, the availability of The Species of Rhododendron resulted in English horticulturalists thinking almost exclusively in terms of Series, while their counterparts on the Continent and in the U.S.A. mostly continued to refer to the subgenera and sections of the older botanical arrangement though more recently the Series have made ground in the United States. It was Dr. Sleumer who, in 1949, provided a synthesis of these two approaches by distributing the various Series into the appropriate pigeon-holes of the older system. In this way the advantages of both systems were combined into one. In spite of this, his proposals have been little used, no doubt because they have not been available in an English version.
In a recent issue Mr. Peter Cox has expressed fears if more than one classification come into use. But there are no signs that any new classification will compete with the one already established. My wife and I have published a history of the classification of the genus (in Notes from the Royal Botanic Garden, Edinburgh , Vol. 32) and have also summarized the evidence used at the present day (in the Rhododendron Year Book for 1970). Both these accounts show how new lines of evidence have always confirmed, strengthened and improved the old established classification. It cannot be supposed that the main outline of this will ever be cast aside for something quite new.
So far I have referred to broad classification - major subdivisions - but there is also a fear that multiple classifications will come into being as separate groups of species are revised. Since no one can suppose that the present botanical treatment of species is satisfactory, the revision of groups, and eventually of the whole genus, must be encouraged. This would only result in duplication if the old treatments are not discarded as they are revised. In any event any botanist is free to revise any group of plants he chooses and fortunately no authority exists to control his efforts. Naturally everything new is not an advance, but it is certain that no advance will be made unless new revisions are encouraged.
The botanical chaos created in rhododendron in the late 19th and early 20th centuries, which now must be resolved, is typical of botanical progress. The first fragmentary collections from a region are enthusiastically turned over and with so few specimens all appear different and are given names (one subspecies of R. nivale embraces nine early species). Thirty years ago I was caught up in a wave of new plants from central New Guinea. Recently I have had to reduce several of my own species which the ample collections now available show to be merely parts of the range of variability of one species.
In one respect (but I hope not in others) botany and horticulture make uneasy bedfellows - that is over the concept of species. To a botanist a species is a very fluid concept. Often, it ranges far and wide over a continent, changing its aspect as it goes. If a continuum of this kind displays recognizable differences in different parts of its range it is convenient to refer to these as subspecies, for example, many of the resident birds of Britain are subspecies of continental forms. It is the variety within a species that appeals to a botanist, but he applies names to these numberless aspects of one species only if they are reasonably constant over a geographical region. Mr. Peter Cox also expressed uneasiness about the use of subspecific
names, because he fears this category may be used to perpetuate names for the sake of horticulturalists. But this is unlikely. As we have seen, the category is useful by giving recognition to geographical races. Mostly, it will be used in cases which have no horticultural interest, and botanists are unlikely to treat groups with horticultural value any differently from the rest of the plant kingdom.
Variations of all kinds may interest a botanist, but when making a garden you hope to secure the best form of a species, or at least the best form that is in cultivation. Also you expect all the plants carrying the same name to be alike. That is, you expect standardization of nursery stock so that a given name always means the same thing. For that matter, several forms of the same species may be desirable each for their different features, and the gardener will naturally expect each of these to be known by a distinctive name. Botanical nomenclature is not designed for this purpose, with the result that horticulturalists may wonder how two very different plants are required to go under the same name. To the botanist the differences are merely part of the great and often continuous variation found in the field, but to the gardener they are selected and important forms.
Plant nomenclature does provide a solution to this dilemma. Forms of species which have been brought into cultivation may be given a distinctive name (not in the "Latin" form of botanical names) and there may be as many of these within a species as seems necessary. If this practice were adopted more consistently, the conflict between the botanical names of species and the requirements of those who collect them in gardens would be resolved.


  • Philipson, M. N. & Philipson, W. R. (1970) The Classification of Rhododendron. The Rhododendron and Camellia Year Book 25: 1-8
  • Philipson, M. N. & Philipson, W. R. (1974) History of Rhododendron Classification. Notes Roy. Bot. Gard. Edin , 32, 223-238
  • Seithe, A. Geb. v. Hoff (1960) Die Haarformen der Gattung
  • Rhododendron L and die Moglichkeit ihrer taxonomischen Verwertung. Bot. Jahrb . 79 297-393.
  • Sleumer, H (1949) Ein System der Gattung Rhododendron L. Bot. Jahrb , 74, 511-553
  • Stevenson, J. B. led.) (1930) The Species of Rhododendron , London