The RHS Advisory Panel on Nomenclature and Taxonomy
Chris Brickell and Piers Trehane
(This article first appeared in The New Plantsman 4(2):115-119, 1997)
For many years the RHS has been involved in work to stabilise the names of cultivated plants, mainly through the publication of International Registers for specific genera or groups of genera such as Narcissus, orchids, conifers and rhododendrons. This has been done with the primary aim of avoiding or minimising the inevitable confusion that occurs not only among gardeners but in the wholesale and retail nursery trades, and linked industries, when the names of plants are changed or when two cultivars in the same genus are given identical names. RHS input into clarifying the muddy waters of botanical and horticultural taxonomy and nomenclature dates back to the early part of this century and perhaps the main achievement to date has been the formulation, preparation and eventual publication of the International Code of Nomenclature for Cultivated Plants (ICNCP) by Professor (then Mr.) William T. Stearn in 1953. Since that date this "Cultivated Plant Code", which provides rules for governing the use and formation of taxonomic groups of cultivated plants (primarily the cultivar and cultivar-group), has been revised and refined several times.
Recently the 5th edition of ICNCP (Ed. C.D. Brickell et al, 1980) was revised thoroughly after wide consultation and a new and greatly expanded edition was then published (Ed. P. Trehane et al, 1995). This internationally accepted publication has helped markedly to improve the stable use of plant names in cultivation. There is still, however, great concern among gardeners over what seems to be a constant stream of name changes of widely grown and familiar garden plants highlighted to some extent by the annual publication of The RHS Plant Finder in which many nomenclatural changes have been included each year thus creating a heightened awareness of taxonomic and nomenclatural adjustments. Whilst the RHS has been very actively involved in stabilisation procedures it did not establish a formal body to consider these matters until 1995 when the RHS Advisory Panel on Nomenclature & Taxonomy was established. This Panel includes individuals from a number of organisations who are working on horticultural taxonomy in the UK and have considerable experience of both horticultural and botanical systematics.
The main remit of the Panel is to act as a catalyst to develop a system for stabilising usage of the names of plants grown in the UK that takes into account both the needs of gardeners and the horticultural industry as well as adhering to the principles of the International Code of Botanical Nomenclature (ICBN or Botanical Code) which is the principal standard for forming and maintaining correct names of taxonomic groups of plants, for the most part those occurring naturally in the wild.
The latest edition of the ICBN, the Tokyo Code, edited by W. Greuter et al, was published in 1994. One of the members of the Panel serves on the Editorial Committee of ICBN whilst three members currently also serve on the Editorial board for ICNCP, providing invaluable links between the two Codes and the Panel.
The reasons for the changes in plant names that concern gardeners and the horticultural industry so much often result from expanded knowledge of particular plant groups following detailed investigation and research. In some cases they occur because an earlier validly published name for a particular plant is discovered which under the rules of the International Code of Botanical Nomenclature is considered the correct name - a nomenclatural change based on the rules of priority.
There is, however, an opportunity now to put forward the conservation of specific epithets when certain criteria (e.g. economic importance) are met. Erica carnea, now conserved in place of the substituted E. herbacea, an earlier name, is an example.
Others may be due simply to errors in identification by botanists or horticulturists. This occurred with Euryops acraeus which was introduced into the UK un-named and later verified incorrectly as Euryops evansii. It was then discovered to have been identified incorrectly, the true E. evansii being a very distinct species; in such a case it is essential to correct the error.
In both instances - an earlier validly published name and an error in identification - the need to correct the names may readily be seen to be justifiable and are usually accepted without much criticism from gardeners particularly if the reasons are explained fully.
More controversial from the horticultural viewpoint are the name changes resulting from taxonomic revisions particularly where they upset well-established names of long-cultivated plants. It may be argued that it is simply a matter of taxonomic opinion, for example, whether or not a genus is split into two or more genera or two or more genera are combined. Similarly one or more species may be united or a species separated into two or more taxa; or the rank may be changed from subspecies or varietas to species or vice-versa.
Such fluidity in taxonomy may seem to gardeners and horticulturists - as well as some botanists not involved in systematics - somewhat arbitrary.
These views are strengthened when generic "splitting" occurs with such well-known genera as Chrysanthemum (now segregated or re-segregated into several genera); or when proposals to unite or re-unite ("lumping") of other genera such as Mahonia & Berberis or Epilobium & Zauschneria are promulgated. To many people this is seen to be "fiddling with generic limits" unnecessarily. These taxonomic movements not only affect the status of the genera involved but may, in some cases, require the provision of different specific epithets in a "combined genus", often with other nomenclatural twists and turns occurring as well.
There is no doubt that, in the vast majority of cases, these taxonomic merry-go-rounds are based on very sound scientific research combining modern techniques such as cladistics and DNA analyses with morphological and other traditional methods. But even using this battery of taxonomic techniques there are differences of opinion depending on the "weight" of importance given by individual taxonomists to particular characters on which their taxonomic decisions are based. This may in some instances result in different treatments being published by two taxonomists working on the same genus, the differences simply reflecting distinct taxonomic viewpoints. It is equally a matter of opinion which treatment should be followed - a flexibility that applies to any area of the natural sciences.
As the major users (and promoters) of plant names, gardeners and horticulturists find such apparent ambivalence frustrating and this has long been a source of great irritation. Taxonomists will say, rightly, that there is nothing to stop gardeners using names that are familiar and well understood by them if they wish to do so. If, for example, gardeners wish to use Veronica to incorporate all the plants described not only in Veronica, but in Hebe, Parahebe, Derwentia and other segregates as well, they have a perfect right to apply this broad generic concept. But differences of opinion between gardeners over such a "lumping" approach would almost certainly be greater than those between taxonomists and it is essential to establish a system whereby the changes to plant names used in horticulture are limited and amended only after careful assessment of the effect such changes would produce. This forms part of the remit of APONAT at least for the UK.
The impracticability of keeping up-to-date with all taxonomic research and name changes - even with I.T. - is obvious and it is also untenable to develop a satisfactory system to allow a review of taxonomic research world-wide that would assess the quality of the taxonomy - currently it is only peer acceptance that slowly helps to establish the quality of such research.
The provision of a stable system of usage of plant names is, however, of vital importance to the horticultural profession and industry as well as to gardeners. The establishment of this Panel by the RHS is a step in this direction, building on the initiative of the John Gilmour (former Director of Wisley and later of Cambridge Botanic Garden, previously Assistant Director of RBG Kew) who proposed a system of "Horticultural Equivalents", names commonly used in horticulture although their taxonomic status had changed. This was developed and used in the International Orchid Register produced by the RHS because of the differences of view over generic delimitation and has long been maintained for horticultural purposes in this publication.
The Panel has been concerned initially mainly with the nomenclature to be used in the RHS Plant Finder and has established a number of standards on which to base its decisions.
Apart from the essential standards of ICNCP and ICBN already referred to earlier in this article, the Panel has decided to use a number of internationally recognised standard works to carry out its remit. In particular note has been taken of the Names in Current Use (NCU) Project that is promoted, amongst others by the International Association of Plant Taxonomists (IAPT), and the Panel has elected to use as a standard Names in current use for extant plant genera,(NCU-3), W. Greuter et al, for the spelling of generic names in the Society's publications.
For flowering plants, genera are allocated their family designations according to R.K.Brummitt, Vascular plant families and genera, Royal Botanic Gardens, Kew, 1992. This publication uses the classification employed in the herbarium at Kew and while not pretending to be definitive, represents a welcome and pragmatic solution to the often difficult problem of which formal classification one should accept.
Fern genera and families have been treated rather differently. Long before the Society took over The Plant Finder, a treatment for ferns was developed by Piers Trehane and his Index Hortensis Project (in consultation with fern experts) using as a base reference the late K.U.Kramer's contribution to Volume 1 of K.Kubitzki, The families and genera of vascular plants (1990).
The Plant Finder does not generally use author citations after names as is usually found by botanical convention, such information being comparatively unimportant for gardeners, but when author citations do have to be used to distinguish a name of one author from that of another such as happens when a name is confused in the nursery trade, the author's name is abbreviated according to those in R.K. Brummitt & C.E.Powell, Authors of plant names, Royal Botanic Gardens, Kew, 1992.
A number of nurseries sell plants under collectors numbers and at the moment there is no universal way of allocating collectors numbers, this being left to the individual collector or collecting team who generally keep records of each collection made under their own particular numbering scheme. Collection numbers are usually prefixed with a letter or combination of letters and members of the Panel are currently working with others in an international effort to collate these numbers (and there are thousands of them) so that in the future a common standard may be provided.
In reaching decisions on the plant names to be used in future editions of the RHS Plant Finder the panel takes into account the effect taxonomic name changes may have in horticulture but is fully cognisant of the importance of the need to ensure that the international rules of nomenclature are maintained as the scientific names of plants are determined by taxonomists working within the rules laid down under ICBN and ICNCP.
These rules provide the single correct name for a taxonomic group of plants in any one taxonomic "position". Thus, when the taxonomists working on a group of plants agree a taxonomic position that agreement becomes manifest in their acceptance and use of the same name. It has to be remembered, however, that taxonomic consensus in one era may not be fully endorsed by taxonomists at a later date whose research may lead them to different conclusions on the delimitation of genera; species or other taxa.
The Panel does not therefore follow in their entirety the trends promoted by scientists, however expert they are in their field. For example, botanical thinking on the Onagraceae has, for some years, been led by a team at Missouri Botanic Garden. The botanists there, while recognizing the taxon to be distinct, are of the opinion that the genus Zauschneria K.Presl sits within their concept of Epilobium L. To a horticulturalist however, the woody nature of Zauschneria along with the different symmetry of its flowers, as well as other morphological characters, makes the genus quite distinguishable from the willow herbs of Epilobium to the point where recognition of the genus Zauschneria is of value. The Panel therefore supports retention of Zauschneria for horticultural purposes.
Equally, the Panel does not shirk from "sinking" a genus when scientific opinion is overwhelming and especially if the genus is of little horticultural importance. The genus Symphyandra was establisshed by Alphonse de Candolle in 1830 to accommodate a number of species that differed from Campanula L. in the arrangement of the anthers. It has been demonstrated that the particular difference in anther arrangement represents an easy evolutionary step and that such a step could occur many times - hardly a good character on which to base a genus. In Symphyandra this has happened with a small group of Caucasian species as well as with Mediterranean and Eastern Asian species. Not surprisingly, major works such as Czerepanov's 1995 checklist of the former USSR and the Med-Checklist (Greuter et al. 1984) have sunk Symphyandra into Campanula. This view is shared by Campanulaceae specialists including the Russian A. A. Kolakovsky who is well-known for segregating many genera from Campanula. After taking expert advice from Dr Tom Lammers of the Field Museum in Chicago, the Panel decided not to maintain Symphyandra as a genus but to treat it as a synonym under Campanula. This action has also negated the need to create a hybrid genus name to cover recent hybrids between the two genera; such intergeneric hybrids are otherwise unknown in the Campanulaceae.
In deciding whether or not to recommend a name change at the generic level, the Panel is only too aware that such a change today may be reversed all too soon if the taxonomy of the group in question is not fully understood or if proposed changes are not accepted within the scientific community working on the group. It has been recently suggested that the two genera Gaultheria L. and Pernettya Gaudich. be merged under the earlier name Gaultheria, but dissent within the taxonomic community working on the Ericaceae has been noted as the proposal has been rejected in some floristic works. Similarly, it has been proposed to merge Mahonia Nuttall within Berberis L. in the forthcoming Flora of North America. The Panel feels that more scientific work needs to be done on these groups before recommending the demise of the names of two genera which are well understood by horticulturists as well as many botanists.
Proposals to create new genera and to merge the old are continually being published and the panel has to keep a watchful eye on the botanical literature as well as remaining in touch with taxonomic developments throughout the world to ensure that names important in the world of horticulture are kept up to date with scientific thought. At the family and genus level at least, by the application of clear standards and the careful vetting of changes in taxonomic opinion,
The Panel is intent on following its remit to develop a system of stabilising names in horticultural usage, consistent with the principles of the ICNCP and the ICBN, that will provide a standard for the nursery industry, gardeners and horticultural publications for the future. Much remains to be done and in future issues of the New Plantsman further articles on the work of the Panel will be published including a continuing series of Nomenclatural Notes produced as a result of the work of the Panel.
In the next issue an article by Dr Alan Leslie will highlight some of the other areas on which the Panel has been concentrating during its recent deliberations.
The Panel welcomes comment and input into its work and any correspondence relevant to the nomenclatural and taxonomic issues that come within its remit should be sent to Dr Alan Leslie, Secretary to the Panel, RHS Garden Wisley, Woking, Surrey GU23 6QB.
Chris Brickell, Chairman, RHS Advisory Panel on Nomenclature & Taxonomy
Piers Trehane, Hampreston Manor, Wimborne, Dorset BH21 7LX