JARS v63n1 - How Plants Get Too Many Names

        In preparing a high-school biology report seventy-odd years ago, I was fortunate in finding a copy of Liberty Hyde Bailey's How Plants Get Their Names. Reading that sparked my interest - as an amateur - in botany and botanical nomenclature that persists to this day. I hope that the following comments will promote understanding of nomenclatural practices and convince others to stop using incorrect names such as Rhododendron nudiflorum and R. roseum.

        The system of botanical names, detailed in the International Code of Botanical Nomenclature (ICBN), is designed to ensure that a taxon (a taxonomic group; e.g., a species) has one and only one correct Latin name, the earliest that accords with the rules. The name of a taxon is meant only to be a means of identification, not as a descriptor of the history or characteristics of a plant. (Nevertheless, many specific epithets are commemorative or descriptive.) Vernacular (common) names for a given plant often vary between localities, ethnic and linguistic traditions, and countries. The Latin botanical names are universal.
        A goal of the ICBN is to provide stability in nomenclature. Admittedly, this statement has been known to produce loud guffaws from unbelievers. In conversation, we often use the phrase "It's a jungle" in referring to complex relationships of many sorts. The phrase is apt for the complexity of relationships in the vegetable kingdom - a complexity reflected in the rules that govern naming members of that kingdom.
        Understanding a few basics of the ICBN may promote acceptance of name-changes necessitated by application of the code. The concepts of "type" and "priority" are key. A botanical name is permanently attached to a nomenclatural type (an herbarium specimen or, prior to 2007, an illustration) designated by the author when a new name is published. A consequence of the name's being permanently attached to its nomenclatural type is illustrated by the fate of R. bakeri (Lemmon & McKay) H.H. Hume. When Kron examined the type for this name, she found it to be a hybrid (probably R. flammeum x R. canescens). Thus, because application of the name R. bakeri is inextricably linked to its type (the hybrid herbarium specimen), the name is not correct for the red azalea of the Cumberlands - the plant that Lemmon had intended to name. The correct name for the latter plant is now R. cumberlandense E.L. Braun. The date of valid publication establishes the priority of a name; later names for the taxon are incorrect.
        The starting point for modern botanical nomenclature is the Species Plantarum (1753) of Linnaeus. The Linnaean species of azaleas will provide some examples of name changes and name proliferation, but it is necessary first to note briefly the Linnaean classification and reasons why it was displaced by so-called "natural" systems and - after Darwin's 1859 publication of The Origin of Species - by systems intended to show evolutionary relationships.
        Before Linnaeus published Species Plantarum, botanists identified plants by means of phrase-names; e.g., the plant that came to be recognized as Azalea indica L. earlier had been called Chamaerhododendron exoticum, amplissimus floribus liliaceis (Dwarf-rhododendron foreign, very many funnel-shaped flowers) by Breyne. Faced with the daunting task of bringing order into the publication of some 6,000 species, Linnaeus used two shortcuts to simplify identification of a plant and assist the reader in finding descriptions and references in the earlier literature.
        The first shortcut was creation of an artificial, numerical system of classification based on the number of stamens and pistils found in a genus. The six species listed in Azalea by Linnaeus are in the class Pentandria Monogynia (five stamens, one pistil); the five in Rhododendron are in Decandria Monogynia (ten stamens, one pistil). Although this so-called sexual system provided the organizing principle for a wonderfully accessible compendium of the plants known in 1753, it soon proved inadequate to deal with the influx of new plant material from the Orient and America. Botanists observed much greater variation within species than had been recognized previously, and attention turned to "natural" systems that embraced a broad range of morphological characters. By 1840, the Linnaean sexual system of classification had been largely displaced. As we know today, there are azaleas with 10 stamens and rhododendrons with less than 10 and as many as 20-odd stamens.
        Linnaeus's second shortcut became the basis for modern binomial nomenclature. The Linnaean "specific name" for a plant consisted of the genus name and a brief phrase to differentiate the character of the species; thus, Azalea floribus subsolitariis, calycibus pilosis (flowers mostly solitary, calyx hairy) was Linnaeus's specific name for A. indica. For this entry, he placed indica in the margin; this was the "trivial name," which has become the specific epithet of modern binomial nomenclature. A modern binomial plant name comprises a genus name and a specific epithet; e.g., Rhododendron indicum.
        In the late 1700s and early 1800s, the greater flow of seeds and plants from distant regions meant that botanists were increasingly able to base classification decisions on live material. Not only were there more plants to name, but a new plant from the Orient might come to the attention of botanists in England, France, and the United States at almost the same time and might become known by a different botanical name in each country. Even today, with the much greater distribution and availability of journals in which new names are published, some superfluous naming of new taxa occurs.
        Many reasons can be advanced to explain a multiplicity of names for a given plant. Botanists may disagree in their concepts of what constitutes a species; how wide or narrow a range of plant characteristics is appropriate for a species or how major or minor a character difference must be to affect a taxonomic decision (lumpers vs. splitters); or how much weight is given to observations in native habitats vs. study of herbarium specimens and plants in gardens. Other reasons include ignorance of a previously published name; or exploitation of more profound knowledge resulting in new combinations that place a species in a different genus, change the rank of a taxon, or create a new subdivision of a taxon.
        To illustrate the ways in which a multiplicity of names may accumulate for a given species, we will turn back to the beginning of modern botanical nomenclature: Species Plantarum (1753). But it is first necessary to dispose of the "Azalea Indica" that Sims published in the Botanical Magazine in 1812. The plate accompanying Sims's description (see The Azalean 22(3):cover illus.; 29(2):28-29) depicts R. simsii Planch., a Chinese plant with leaves 3-7 x (0.6-)1-2 cm and corolla 25-60 mm (in contrast, the southern Japanese R. indicum has leaves 2-3 x 0.8-1 cm and corolla 30-50 mm). Sims mentions both evergreen and deciduous leaf habit and a color range including yellow (not found in the evergreen azaleas). It appears that Sims, like others of his period, used the term "Indica" (literally, "of India") as a catchall for azaleas from the East. In 1921, E. H. Wilson observed: "For nearly a century and a quarter this plant [i.e., R. simsii DHV] has usurped the name indicum..." A selection of names using the epithet indica or indicum for azaleas other than R. indicum (L.) Sweet is in Table 1. The list includes plants of eight species other than the Linnaean Azalea indica.

The Linnaean Azaleas
The six species listed in genus Azalea by Linnaeus are discussed below. To illustrate various influences resulting in the creation of new names for a species that already has a legitimate name, a selection from the extensive synonymy for A. indica is presented in Table 2.

        A. indica. - Although the Linnaean trivial name for this species continues to serve as the specific epithet, a sizable synonymy accumulated. Some authors created names that reflect variant appearance of plants in the species; e.g., R. decumbens (prostrate, with tips growing upward); A. crispiflora (irregularly wavy petals); and A. macrantha (large flowers). Some of the names are merely new combinations reflecting a change of genus between Rhododendron and Azalea. Names incorporating epithets at infraspecific ranks (subspecies, variety, form) often reflect minor morphological differences of primarily horticultural concern; examples may be found in Table 2 entries attributable to Blume, Maximowicz, and Millais. Many of the plants listed in Table 2 are shown as cultivars in the International Rhododendron Register and Checklist, 2d edition. The species was placed in Rhododendron in 1832 and is now cited as R. indicum (L.) Sweet.
        A. pontica. - When Sweet undertook the transfer of the Pontic azalea to Rhododendron in 1830, he was unable to retain the Linnaean trivial name as an epithet. In the second edition of Species Plantarum (1762), Linnaeus had named the Pontic elepidote rhododendron as R. ponticum, blocking use of that name for the azalea in genus Rhododendron. Sweet selected a new specific epithet, luteum (yellow), which recalls the striking flower color of R. luteum (L.) Sweet.
        A. lutea. - To put it bluntly, Linnaeus made a mess of this one! His specific name for this plant was Azalea foliis ovatis, corollis pilosis, staminibus longisssimus (leaves ovate, corolla hairy, stamens very long). This was followed by phrase-name synonymy citing earlier publications by Gronovius, Linnaeus, Colden, and Plukenet. According to Blake, writing from the Gray Herbarium, the Gronovius name refers to R. canescens (Michx.) G. Don; the Linnaean name cited from the Clifford Herbarium refers to R. nudiflorum (L.) Torr., an illegitimate name to which some in the horticultural community still cling; the Colden phrase-name, which includes flore luteo (flowers yellow), appears to match R. calendulaceum (Michx.) Torr.; and the correct application of the Plukenet name is, according to Blake, "scarcely determinable."
        In the second edition of Species Plantarum (1762), Linnaeus emended the entry for this species by adding two bibliographical citations (Kalm and Duhamel) after the specific name, repeating the phrase-name synonymy from the first edition, and adding another citation (Trew) after the phrase-name from the Clifford Herbarium. Linnaeus also qualified the habitat description (Virginia) as dry and added a descriptive phrase noting that the stamens are twice the length of the corolla, thus more clearly pointing to the plant now correctly named R. periclymenoides (Michx.) Shinners. The trivial name for the species so identified was changed from lutea to nudiflora! Unfortunately this created a name that is illegitimate under modern rules, because its publication included the type of the earlier validly published A. lutea L. The transfer of this species to Rhododendron finally occurred in 1962, but the epithet lutea could not be retained because of Sweet's 1830 publication of R. luteum for the Pontic azalea. The next available name for the species was A. periclymenoides Michx., now known as R. periclymenoides (Michx.) Shinners.
        A. viscosa. - In 1824, this species was transferred to Rhododendron as R. viscosum (L.) Torr.
        A. lapponicum. - A lepidote rhododendron (with 5-10 stamens!), this species was transferred to Rhododendron in 1812 as R. lapponicum (L.) Wahlenb.
        A. procumbens. - Although this plant conforms largely to Linnaeus's description of the genus Azalea, it differs in one important respect. Linnaeus, in Genera Plantarum (1743, 1754) described the seed capsule of Azalea as five-celled, but that of A. procumbens is 2- 3-celled. In 1813, Desvaux placed the plant in a new monotypic genus, Loiseleuria, as L. procumbens. In 1891, O. Kuntze (whose proclivity for renaming plants is legendary) published Chamaecistus procumbens (L.) Kuntze. This action was challenged, and a decision made under the rules governing botanical nomenclature conserved the genus name Loiseleuria Desv. with L. procumbens (L.) Desv. (Azalea procumbens L.) as its type.

Other "problem" species
The Linnaean azalea species are not the only ones to have caused nomenclatural confusion. Two examples will be given: R. roseum and R. obtusum. Under modern nomenclatural rules that have retroactive effect, the first of these was doomed from the start. In naming A. rosea in 1812, Loiseleur-Deslongchamps cited the earlier A. canescens Michx. as a synonym, thus including the type of an earlier validly published name and making A. rosea superfluous and illegitimate. While commenting that A. rosea had not been used in botanical works since 1812, Rehder in 1921 (under older, now superseded nomenclatural rules) created the new combination R. roseum (Loisel.) Rehder and named two forms. Rehder's names have now become synonyms in three species: R. canescens, R. austrinum, and R. prinophyllum. Shinners in 1962 pointed out that the correct name for the fragrant (often described as "clove-scented") species of our eastern and south-central states is A. prinophylla Small or R. prinophyllum (Small) Millais.
        Many of the problems associated with the naming of Japanese plants that reached western countries in the 1700s and early 1800s were the result of Japan's stringent limitation of entry and travel by foreigners. The early western collectors in Japan such as Kaempfer (1690-92) and Thunberg (1775) found it impossible or nearly so to explore for plants in their native habitats. Heavy reliance had to be placed on Japanese collectors, and the provenance (wild from native habitat or cultivated) of many plants was questionable.
        Greater access to peripheral regions followed the opening of commerce after Commodore Perry's 1852-54 expedition, but more extensive opportunities for plant exploration came only after the Meiji Restoration in 1867. Language was, of course, a barrier to communication between local dialects as well as with foreigners. Moreover, a given Japanese plant name might apply to different plants in different regions. Complicating the matter was the fact that there had for long been interchange of plants between Japan and China, and some Japanese species were introduced from China. A further complication was the extent to which Japanese gardeners had hybridized azaleas. According to E. H. Wilson, the type cited by Lindley for his A. obtusa was a garden form; Chamberlain has stated (pers. comm., 2002) that the type appears to be hybrid. Whatever the merits of Lindley's name, it provided the specific epithet for the new combination R. obtusum (Lindl.) Planch. and spawned a host of varieties and forms.
        In their 1990 revision of Rhododendron Subgenus Tsutsusi, Chamberlain and Rae place R. obtusum in a section entitled "Doubtful or Incompletely Known Taxa." They state: "R. obtusum and many of the forms and varieties described within it are cultivated selections of R. kaempferi and R. kiusianum or of hybrids between these two species... The Kurume azaleas may have arisen from the same complex of species." Clearly, R. obtusum is not a "good" species. Unless a plant labeled R. obtusum can with confidence be assigned to R. kaempferi or R. kiusianum, it should in my view be assigned to "Obtusum Group" as a cultivar and not be identified as to species. Both the ICBN and the International Code of Nomenclature for Cultivated Plants contain provisions for the use of epithets from botanical names as cultivar epithets when the plant group concerned is considered to be a cultivated variety.

Retrospect and Prospect
The nomenclatural history of azaleas yields a pattern of progressive development in the acquisition of plant material, in analytical bases for taxonomic decisions, and in achievement of international agreement on nomenclatural rules. The last of these has not been addressed in this article, but suffice it to note that a bitter discord separated the nomenclatural practices of European and American botanists from the late 1800s to 1930.
        In the 1700s and early 1800s, botanical taxonomy centered in Europe. New plants from the Orient and America arrived in small numbers: some were introduced by seed, some by traders or sea captains. Plants were an important component of the materia medica of the day, and collectors were often medical doctors attached to trading companies or were missionaries located in or near seaports. As a result, much of the plant material reaching western countries had been obtained from gardens, temple grounds, nurseries, or other sources of cultivated plants. Frequently, information detailing provenance of the plants was minimal or lacking. A large part of the material from which taxonomists of the day made their judgments was in the form of herbarium specimens or drawings sent by the collectors.
        Little wonder, then, that nomenclatural problems accompanied the early expansion in the flow of new plants to Europe. At first the new plants were viewed largely as horticultural curiosities and, as today, minor differences drew attention and led to new names. Soon, however, collection opportunities and collection techniques improved, and by the mid-1800s the era of large-scale professional plant exploration had begun. The availability of more plant material collected from wild populations, together with improved documentation of the collections, placed botanists in increasingly favorable conditions to make sound taxonomic decisions.
        In the past half-century, the results of field studies came to be incorporated increasingly in analytical processes leading to taxonomic decisions. In Rhododendron, for example, some species had been named in the early 1900s from individual plants (or small groups of plants) grown in botanical gardens; many of these plants were forms selected for horticultural excellence or novelty. Later, when botanists visited the mountain slopes of Asia and saw the natural variation in populations, some of the variant plants that had been named were seen to be simply members of previously named species.
        Advances in plant morphology, anatomy, and physiology - as well as the now not quite new science of molecular biology - offer the possibility of revolutionary advances in taxonomy. Realizing this potential calls for an integration of elements of the traditional and the new taxonomies.
        Ultimately, the processes of life are under genetic control, and the key to unlocking the mysteries is held by the molecular biologists. Unfortunately, many of them appear to hold as final and immutable the results of what may be at best a partial analysis of the evolutionary relationship among a group of plants. Realization of the full potential of the new techniques calls not only for more complete analysis of plant genomes but also for refinement of the computer models used in processing molecular data to assure recognition of all evolutionary branching patterns found in nature.

Acknowledgements
The author extends thanks to Dr. Alan Whittemore of the U. S. National Arboretum for guidance through sticky wickets of the Botanical Code and to Mr. William C. Miller III, whose comments on redundant plant names prompted my writing of this article. All opinions, infelicities, or errors are the sole responsibility of the author.

References
Blake, S.F. 1918. Notes on the Clayton Herbarium. Rhodora 20:53-54.
Brickell, C.D. et al. 2004. International Code of Nomenclature for Cultivated Plants (ICNCP). Leuven: International Society for Horticultural Science.
Chamberlain, D.F. & Rae, S.J. 1990. A Revision of Rhododendron: IV Subgenus Tsutsusi. Edinb. J. Bot. 47(2):89-200.
Chamberlain, D. et al. 1996. The Genus Rhododendron: Its Classification and Synonymy. Edinburgh: Royal Botanic Garden Edinburgh.
Kron, K.A. 1993. A Revision of Rhododendron Section Pentanthera. Edinb. J. Bot. 50(3):249-364.
Lawrence, George H.M. 1851. Taxonomy of Vascular Plants. New York: The Macmillan Co.
Leslie, Alan C., comp. 2004. The International Rhododendron Register and Checklist. 2d ed. London: The Royal Horticultural Society.
Linnaeus, Carl. 1957. Species Plantarum: A Facsimile of the First Edition 1753. Vol. 1. London: British Museum (Natural History); for The Ray Society.
McNeill, J. et al. 2006. International Code of Botanical Nomenclature (Vienna Code; ICBN). Ruggell, Liechtenstein: A.R.G. Gantner Verlag; for the International Association for Plant Taxonomy.
Rehder, Alfred. 1921. Azalea or Loiseleuria. J. Arnold Arbor. 2:156-159.
Wilson, E.H. & Rehder, Alfred. 1921. A Monograph of Azaleas: Rhododendron Subgenus Anthodendron. Cambridge, Massachusetts: University Press; for the Arnold Arboretum.