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Taxonomists classify organisms in a variety of ways, but in general three nested categories are in common use: families, genera (the singular is genus) and species. Families are made up of genera that share features they have all inherited from a common ancestor. Family names are instantly recognisible by virtue of their endings — in zoology family names end in '-idae'; all parrots and allies are members of the family Psittacidae, for example. In botany, family names end in the suffix '-aceae'; all magnolias for example are members of the family Magnoliaceae. Some people still use the now outdated family names with different endings — such as Cruciferae for what is know known as Brassicaceae and Palmae for what we now call Arecaceae. This may seem like change for change's sake, but it allows non-specialists to know just what level in the hierarchy we are talking about. A genus is a more narrowly defined grouping that contains species that share characteristics; a single species has unique characters that distinguish it from all other organisms.

The scientific names of plants, animals and micro-organisms are based upon Latin, a seemingly archaic anachronism. One simple reason for this is that Latin was the language of scholarship in the beginning of the scientific age. But there is a more important reason for the use of scientific names. A plant or animal may have many common names, depending on where you are: for example, plants with the scientific name Hyacinthoides non-scripta (L.) Chouard ex Rothm. are called bluebells in England, but in the United States and Scotland, the common name bluebell refers to members of the genus Campanula, in a completely different family. In much of the English-speaking world the common name 'Yam' refers to several species in the genus Dioscorea, but in the south-eastern United States of America, if someone refers to a 'Yam', they usually are talking about Ipomoea batatas L., the sweet potato. A scientific name makes conversation about organisms international.

In the early days of taxonomy scientists referred to organisms using long Latin polynomials or phrase names, the first word of which was the name of the genus. Linnaeus, a Swedish medical doctor of the eighteenth century and the father of modern botany, revolutionized the way we name plants and animals when he introduced a system of what he called trivial names - single word designations that, in combination with the genus, could serve as a sort of shorthand for the longer, more complicated phrase names. Today these trivial names are what we refer to as the genus and species names of plants and animals. By convention, both the genus and species name are italicized (the family name is most often not), and genus names are capitalized, while species names, also called species epithets, almost never are. Our own scientific name is Homo (the genus) sapiens (the species) of the family Pongidae.

Taxonomists use sets of international rules (see list below) — agreed upon in each community — in order to regulate naming. These rules are followed voluntarily by scientists and, like Latin, may seem archaic, but really bring stability and order to naming, especially necessary now as we face the ever-increasing biodiversity crisis. The scientific naming of plants is governed by the International Code of Botanical Nomenclature, a set of rules and recommendations voted upon by the assembled botanical community every six years at international congresses, the most recent held in St. Louis, Missouri in 1999, the next due to be held in Vienna in 2005. Botanists have been adapting and refining their code of naming — the code of nomenclature — for almost two hundred years — it has evolved with worldwide use. Two of the important sorts of rules in the Code are the type method, described above and the principle of priority — sometimes a bone of contention between gardeners and botanists. Priority is simple — the oldest name, that which was coined first, is the one that is 'legally' correct and the one that we should use. This can be irritating when names with a long history of use in society at large suddenly get changed because an older name has been unearthed — Magnolia denudata had been widely used for the lily-flowered magnolia, until someone found that the species name 'heptapetala' had been published earlier. The name would have had to change, but for the Code's clever 'get-out' of conservation and rejection. This allows botanists to propose a name for conservation — it then becomes the correct name over all earlier names — or rejection — it is rejected as a correct name forever. These rules can be used when stability of usage is threatened, preserving the status quo — but the reasons and justification have to be good; these decisions are not taken lightly! Another reason names change is because ideas about relationships — mostly membership of one genus or another — change. An example of this is the scientific name of the tomato. First described by Carl Linnaeus as Solanum lycopersicum, the tomato was later given its own genus by Philip Miller, who called it Lycopersicon esculentum. Today, we know that the tomato and its relatives are nested within the genus Solanum — they are in fact most closely related to potatoes — so we again call them Solanum lycopersicum. This sort of name change reflects an increase in our knowledge — a scientific advance in knowledge about relationships, even though we are using Linnaeus' original name.

In addition to being understandable across cultures, the scientific name of a plant must also be uniquely identifiable — and taxonomists do this by also adding the surname of the person who coined the scientific name. For example, Robert Brown named a species of the palm genus Livistona as new to science and he called it Livistona humilis. When referring to this plant by its full scientific name, we call it Livistona humilis R. Br. (the standard abbreviation of Robert Brown). This differentiates it from any other 'Livistona humilis' — we all know it is Robert Brown's name we mean. It seems as though no botanist would use a name previously used — but it happened more often that one would think! Today's computerized indices mean there is no excuse for using a name that has been used before. An author's name in parentheses means that he/she originally described the species in a different genus. For example, the German botanist Eduard Frederich Poeppig originally described the Royal waterlily as Eurydale amazonica — its name was Eurydale amazonica Poeppig. Later botanists decided it was sufficiently different from other Eurydale species to warrant being in another genus, and the name Victoria regia had been used. But the species name amazonica is older than the species name regia — it has priority — so the correct name for the waterlily becomes Victoria amazonica (Poepp.) Sowerby — as John Sowerby was the one who finally sorted this all out and made the correct combination of genus and species names. For ease of reading names are often used without their authors, but to be truly correct, the author ought to be included. The careful keeping track of names, along with the people responsible for them, makes it possible for taxonomists to pursue their trade, and is the basis for the common language of biology.

For information about scientific naming:

Brummitt, R.K. & C.E. Powell. 1992. Authors of Plant Names: a list of authors of scientific names of plants, with recommended standard forms of their names, including abbreviations. Royal Botanic Gardens, Kew.

Greuter, W.G., J. McNeill, F.R. Barrie, H.M. Burdet, V. Demoulin, T.S. Filgueiras, D.H. Nicolson, P.C. Silva, J.E. Skogg, P. Trehane, N.J. Turland & D.L. Hawksworth. et al. 2000. International Code of Botanical Nomenclature. Regnum vegetabile 138. Königstein. (the 'Saint Louis Code' voted on at the 1999 St. Louis International Botanical Congress). http://www.bgbm.fu-berlin.de/iapt/nomenclature/code/SaintLouis/0000St.Luistitle.htm

ICZN (International Commission on Zoological Nomenclature). 1999. International Code of Zoological Nomenclature, 4th edition. London: International Trust for Zoological Nomen. http://www.iczn.org

International Plant Names Index (IPNI) website URL: http://www.ipni.org/index.html

Knapp, S. 2000. Millennium Essay: What's in a name? Nature 408: 33.

LaPage, S.P., P.H.A. Sneath, E.F. Lessel, V.B.D. Skerman, H.P.R. Seelinger, and W.A. Clark (eds.) 1992. International Code of Nomenclature of Bacteria (1990 revision) Bacteriological Code. Washington, DC: American Society for Microbiology. See International Committee on Systematics of Prokaryotes

Text adapted from:  Knapp, S. (2003) Potted Histories: an artistic voyage through plant exploration. Scriptum Editions & the Natural History Museum, London: London.