Botanical name changes – nuisance or a quest for precision ?

To understand the need for the seemingly regular changes to plant names applied to many tropical forage species, it is necessary to be aware of the rules that govern botanical nomenclature. The binomial naming system, first proposed in 1753, is governed by rules defined in the International Code of Nomenclature for algae, fungi and plants (ICN). These rules have been strengthened as necessary over the years in the interest of providing practitioners with plant names that are unique for each species, and presented in an hierarchical format that shows the evolutionary relationships between plants. This paper includes a table of name changes accepted by the USDA Germplasm Resources Information Network (GRIN) for species used in tropical forage research and development over the last half century. The need to use legitimate plant names is emphasized and suggestions are made on how practitioners might best deal with


Introduction
Since the hierarchical system of nomenclature was proposed by the Swedish biologist and medical doctor, Carl von Linné (Carolus Linnaeus), in "Species Plantarum" in 1753, and a set of rules to administer it, "Lois de la nomenclature botanique", was advanced by Alphonse de Candolle in 1867, there has been an ongoing attempt to inject identity and order into what hitherto was simply a naturally occurring assemblage of randomly named organisms.This system, as it has evolved to the current day, requires that plants be named according to a series of basic tenets laid out and expanded on in the International Code of Nomenclature for algae, fungi and plants (ICN) by McNeill et al. (2012), formerly named International Code of Botanical Nomenclature (ICBN), and overseen by the International Botanical Congress that usually meets every 6 years.The system is designed to avoid confusion, not create it, as is often claimed by people who routinely use binomial plant names in their work.

Why not use common names?
Common or vernacular names are those non-scientific names applied locally to a particular plant in a given locality.The main problem with common names is that they are not common; that is, they are not universal.Each country, each state or province within a country and often each district within a state or province, may well have its own common name for a particular plant.For example, the now widespread shrub species known as "guaje" and almost 20 other names in its native Mexico, is also known as "ipil ipil" in the Philippines or "koa haole" in Hawaii, and by different names in virtually every locality where it is currently found.However, regardless of where this plant is growing in the world, it will be identified by botanists as "Leucaena leucocephala".
Another problem with common names is that one common name may be applied to more than one species, particularly if there is a superficial resemblance.For example, the name "sensitive plant" is usually used to refer to Mimosa pudica, but is also sometimes used to refer to another species in the legume subfamily Mimosoideae, Neptunia gracilis, and even to one in subfamily Caesalpinioideae, Chamaecrista nictitans.The characteristic that all 3 species have in common is that the leaflets exhibit thigmonasty (touch-induced movement).
Another issue, as demonstrated in the latter example, is that common names tell nothing about the relationship between plants, a factor that can be important in relation to disease susceptibility or, in the case of legumes, selection of an effective rhizobial strain.Finally, many of the species we sow as forages have no common name in any language, leading to the nonsensical situation of creating common names to satisfy the requirements of a vernacular plant description, as was the case for cultivar registration in earlier years in Queensland, Australia.Mejia (1984) compiled an extensive list of Spanish, English and Portuguese common names to assist practitioners in making the link with botanical names for a large range of more common grasses and legumes.Cook et al. (2005) provide an alternative online source for this connection.

Basic tenets of the ICN
The ICN is an extremely detailed document that has developed since "Lois de la nomenclature botanique" into a very detailed set of rules, covered in 9 chapters and 62 articles, the latest version being known as the "Melbourne Code" (McNeill et al. 2012).The main themes that affect us are: 1.A botanical name for a particular taxon is attached to a type specimen, usually preserved in an herbarium.2. Botanical nomenclature is based upon priority of valid publication after 1 May 1753, the publication date of "Species Plantarum".This means that a more recent species name is to be replaced if an older one, validly published, is discovered.Accordingly, each taxon of a particular circumscription, position and rank should have only one correct name.3. Scientific names are expressed in Latin.4. The rules and regulations of the ICN are retroactive, unless there is an explicit statement that this does not apply.
For a new or alternative name to be considered for acceptance by the scientific community, it must meet the requirements of valid publication.While there are many articles in the Code referring to this issue, some of the major provisos that must be met are: properly Latinized with the correct rank ending (e.g."aceae" for plant families, "oideae" for subfamilies, and "eae" for tribes), ranks simply reflecting a level in the hierarchy.3. The name must be accompanied by a description that will distinguish the taxon from similar or closely related taxa.Prior to 2012, it was essential that a name be published with a Latin description or diagnosis, or with a reference to such.However, the description can now be published in either Latin or English, usually along with a vernacular description, if the original is not in English.4. A nomenclatural type, which is usually a herbarium specimen permanently associated with the name, must be indicated (for genus and below, that is: species, subspecies, botanical variety or form).
Valid publication alone does not guarantee that a name will be accepted.Over time, a proposal is subjected to scrutiny by systematic botanists, who assess the strength of the argument for change or the adequacy of the diagnosis.A validly published name may still be considered illegitimate if it does not follow one or more rules of the ICN.The situation can arise, where one expert or group of experts considers the proposed change sound, while others might reject the change, leading to confusion among practitioners simply using the names.For example, GRIN accepts Pennisetum ciliare (L.) Link as the name for buffel grass, whereas the Catalogue of New World Grasses and Royal Botanic Gardens, Kew, retain the name proposed by Linnaeus, Cenchrus ciliaris L. The only way to ensure that we are referring to a particular nomenclatural type is to follow the plant name with the abbreviation of the author's name according to Brummitt and Powell (1992) for the rank of family, genus, species and subspecific taxon (subspecies, variety or form).

Why names change
Systematic botanists around the world conduct exhaustive library and laboratory research to ensure that names of species are in accordance with the rules of the ICN.In doing so, they might determine that a name, as currently used, is inappropriate under the rules of botanical nomenclature and should be changed for the following reasons:  (Fantz 1996). Similarly, for many years, research and development personnel referred to most Desmanthus species with which they were working, as D. virgatus or D. depressus.Following publication of the Desmanthus monograph (Luckow 1993), it has become apparent that much of the germplasm formerly identified as D. virgatus was, in fact, D. pernambucanus (L.) Thell., while D. depressus was D. virgatus (L.) Willd.Accordingly, it is necessary to be somewhat circumspect about the identity of Desmanthus species in papers published prior to 1993. Some studied species have simply been misidentified.This is a common problem among the more robust Cynodon spp., that bear a superficial resemblance to one another (see C. plectostachyus in Table 1).Tables 1 and 2 summarize name changes as accepted by GRIN, together with some commonly encountered through misidentification.It must be emphasized that this list of species represents those encountered by practitioners working with tropical and subtropical forages, and in no way is intended to be an exhaustive list of legume and grass name changes.Desmodium heterocarpon (L.) DC. subsp.ovalifolium (Prain) H. Ohashi "Desmodium rensonii" 3, 4  Desmodium cinereum (Kunth) DC.Dolichos axillaris E. Mey.
Zornia glabra Desv., Zornia latifolia Sm. and others 1 Most of the "New names" listed are as accepted by GRIN. 2 Some of the species in the "Names previously" column are included by virtue of the fact that they have been used in publications not referenced by GRIN.These are indicated by an asterisk (*). 3 Referring to the plant used in Southeast Asian hedgerow systems. 4Names in inverted commas (" ") are names applied outside of formal publications.

What about higher plant ranks?
Name changes are not restricted to the ranks of genus and below.Even the first rank below Kingdom (i.e.Division/Phylum) has changed from the traditional Angiospermae to Magnoliophyta to be in keeping with the ICN requirement that a higher rank name should have, as its stem, the name of a genus within that higher rank.Similarly, grasses now reside in class Liliopsida and not the traditional Monocotyledonae, and legumes within class Magnoliopsida and not the Dicotyledonae.This same requirement has led to a change in family names, with the added proviso that the generic stem be followed by the suffix, "aceae".The grass family is now widely accepted as Poaceae, although under Article 18.5 of the Code, Gramineae may still be used on the basis of "long usage".
However, the issue of legume family groupings has not been as simple.There has been controversy for some time whether legumes reside in a single family or 3 separate families.For many years, all legumes were placed in the family, Leguminosae, which does not have a generic stem, nor does it satisfy the "aceae" ending.This was solved by placing them all in family Fabaceae, thus satisfying Article 18.1 of the Code.In relatively recent times, legumes were divided into 3 families, Fabaceae (alternatively Papilionaceae), Mimosaceae and Caesalpiniaceae, thus creating confusion between the allencompassing family, Fabaceae, and the more restricted pea-flowered family.There now appears to be sound evidence for a single legume family that Kew botanists, Lewis and Schrire (2003), propose should be named Leguminosae, with 3 subfamilies, Papilionoideae, Mimosoideae and Caesalpinioideae, all in accordance with Article 18 of the Code, even though there is no genus, Papilio, within the pea-flowered subfamily.

Selecting the correct name
A number of reliable websites can be used as sources of currently accepted plant names: GRIN While every effort has been made to establish an infallible system for naming plants, it must be recognized that experts may interpret the literature differently, leading to some inconsistency in accepted names of some species.For example, if we interrogate two of the above databases for the species once commonly referred to as Desmodium canum, GRIN accepts Desmodium incanum (G.Mey.) DC., whereas The Plant List accepts Desmodium incanum DC.Each can provide justification for the determination.In the interest of consistency, it is best to source all names used in a publication from a single reputable authority.As an example, Cook et al. (2005) chose GRIN as their taxonomic authority for the SoFT database.

Conclusion
It is important in reporting research results to be sure the plant names used are as accurate and up-to-date as possible, so the reader is confident of the identity of the species.In the interest of precision, it may be best not only to use legitimate plant names, if applicable, down to the botanical variety level, but also to include the author with the binomial name, when name changes have occurred and there might be a risk of confusion.This need only be done the first time such a species is mentioned in an article.
While results of any interrogation may vary in relation to a currently accepted name, the above sites will indicate the name and author accepted by that particular source.That name will facilitate access to alternatives accepted by other authorities.However, within any one document, it will be important to be consistent with names used.
For research publications, we suggest that, in the case of a new name, the commonly used old name also be cited the first time the plant is mentioned in a given article.Examples: Urochloa (syn.Brachiaria) decumbens [or Urochloa (formerly: Brachiaria) decumbens], Centrosema molle (syn.C. pubescens) [or Centrosema molle (formerly: C. pubescens)].If authors are too uncomfortable with the new name and prefer to continue using the earlier one in a given article, an option could be, e.g.Panicum maximum (now: Megathyrsus maximus), the first time the plant is mentioned.
The aim of any paper is to inform the reader in the least ambiguous way possible on the subject at hand, and www.tropicalgrasslands.info part of this is precise identification of the plants used.In response to the questions implied in the title of this paper, correctly researched and argued name changes that we occasionally encounter may be a slight nuisance, but are essential in our quest for precision.
. With the benefit of closer scrutiny, or using a molecular taxonomic approach, there may be justification for a change of circumscription, which is the definition of the limits of a taxonomic group.This can entail merging of existing taxa, as was the case with Digitaria eriantha Steud., which now includes D. decumbens Stent, D. pentzii Stent and D. smutsii Stent; or the disassembling of an existing taxon, as was the case with the legume genus, Dolichos, initially described by Linnaeus, where some members were retained in Dolichos, while others were reassigned to Lablab, Macrotyloma and Vigna, among others.This apparent "split" has, in part, been brought about through the elevation of the species, lablab, and the subgenus, Macrotyloma, to the rank of genus.4. The name in current common use does not apply to the species to which it is applied.We cite 3 representative examples:  The type specimen of Centrosema pubescens Benth.more appropriately refers to the species formerly known as C. schiedeanum (Schltdl.) 1. Discovery of an earlier, validly published, different name for a particular taxon, which, under the ICN rule of priority, would necessitate the renaming of that taxon.For example, Macroptilium longepedunculatum (Mart.ex Benth.)Urb. was initially used for the Australian cultivar, Maldonado.However, this species, whose name derives from the original name, Phaseolus longepedunculatus Mart.ex Benth., was found to be the same as the earlier-named Phaseolus gracilis Poepp.ex Benth., now accepted as the basionym (the original or first validly described name for a species or other taxon).With the reassignment of a number of species formerly in Phaseolus to Macroptilium, 'Maldonado' now belongs to Macroptilium gracile (Poepp.ex Benth.)Urb.gitimate format as with Stylosanthes guianensis var.vulgaris M.B.Ferreira & Sousa Costa, which is now S. guianensis (Aubl.)Sw. var.guianensis.3R.J. Williams & R.J. Clem., which has a limited natural distribution and is represented by the Australian cultivar, Belalto, while C. molle Mart.ex Benth. is now accepted as the most appropriate botanical name for the naturally widespread species known as common centro

Table 1 .
Name changes in a selection of tropical forage legume species during the past 50 years. www.tropicalgrasslands.info