Taxon

For the journal, see Taxon (journal). For other uses, see Taxa (disambiguation).
African elephants form the genus Loxodonta, a widely accepted taxon.

In biology, a taxon (back-formation from taxonomy; pl.: taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular ranking, especially if and when it is accepted or becomes established. It is very common, however, for taxonomists to remain at odds over what belongs to a taxon and the criteria used for inclusion, especially in the context of rank-based ("Linnaean") nomenclature (much less so under phylogenetic nomenclature).[1] If a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping.

Initial attempts at classifying and ordering organisms (plants and animals) were presumably set forth in prehistoric times by hunter-gatherers, as suggested by the fairly sophisticated folk taxonomies. Much later, Aristotle, and later still, European scientists, like Magnol,[2] Tournefort[3] and Carl Linnaeus's system in Systema Naturae, 10th edition (1758),[4], as well as an unpublished work by Bernard and Antoine Laurent de Jussieu, contributed to this field. The idea of a unit-based system of biological classification was first made widely available in 1805 in the introduction of Jean-Baptiste Lamarck's Flore françoise, and Augustin Pyramus de Candolle's Principes élémentaires de botanique. Lamarck set out a system for the "natural classification" of plants. Since then, systematists continue to construct accurate classifications encompassing the diversity of life; today, a "good" or "useful" taxon is commonly taken to be one that reflects evolutionary relationships.[note 1]

Many modern systematists, such as advocates of phylogenetic nomenclature, use cladistic methods that require taxa to be monophyletic (all descendants of some ancestor). Therefore, their basic unit, the clade, is equivalent to the taxon, assuming that taxa should reflect evolutionary relationships. Similarly, among those contemporary taxonomists working with the traditional Linnean (binomial) nomenclature, few propose taxa they know to be paraphyletic.[5] An example of a long-established taxon that is not also a clade is the class Reptilia, the reptiles; birds and mammals are the descendants of animals traditionally classed as reptiles, but neither is included in the Reptilia (birds are traditionally placed in the class Aves, and mammals in the class Mammalia).[6]

  1. ^ Cantino, Philip D.; de Queiroz, Kevin (2000). International Code of Phylogenetic Nomenclature (PhyloCode): A Phylogenetic Code of Biological Nomenclature. Boca Raton, Fl: CRC Press. pp. xl + 149. ISBN 0429821352.
  2. ^ Magnol, Petrus (1689). Prodromus historiae generalis plantarum in quo familiae plantarum per tabulas disponuntur (in Latin). Montpellier: Pech. p. 79.
  3. ^ Tournefort, Joseph Pitton de (1694). Elemens de botanique, ou Methode pour connoître les plantes. I. [Texte.] / . Par Mr Pitton Tournefort... [T. I-III]. Paris: L’Imprimerie Royale. p. 562.
  4. ^ Quammen, David (June 2007). "A Passion for Order". National Geographic Magazine. Archived from the original on August 27, 2008. Retrieved 27 April 2013.
  5. ^ de Queiroz, K & J Gauthier (1990). "Phylogeny as a Central Principle in Taxonomy: Phylogenetic Definitions of Taxon Names" (PDF). Systematic Zoology. 39 (4): 307–322. doi:10.2307/2992353. JSTOR 2992353.
  6. ^ Romer, A. S. (1970) [1949]. The Vertebrate Body (4th ed.). W.B. Saunders.


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