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Taxon
Grouping of biological populations

In biology, a taxon is a group of organisms classified as a unit by taxonomists, often given a name and rank. Classification systems have evolved from early folk taxonomies to the formalized Linnaean system introduced by Carl Linnaeus in Systema Naturae. Modern taxonomy emphasizes reflecting evolutionary relationships through phylogenetic nomenclature and cladistics, requiring taxa to be monophyletic. However, some traditional taxa like the class Reptilia are paraphyletic, excluding descendants such as birds (Aves) and mammals (Mammalia). Formal names follow nomenclature codes to ensure correct usage.

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History

The term taxon was first used in 1926 by Adolf Meyer-Abich for animal groups, as a back-formation from the word taxonomy; the word taxonomy had been coined a century before from the Greek components τάξις (táxis), meaning "arrangement", and νόμος (nómos), meaning "method".89 For plants, it was proposed by Herman Johannes Lam in 1948, and it was adopted at the VII International Botanical Congress, held in 1950.10

Definition

The glossary of the International Code of Zoological Nomenclature (1999) defines11 a

  • "taxon, (pl. taxa), n.
A taxonomic unit, whether named or not: i.e. a population, or group of populations of organisms which are usually inferred to be phylogenetically related and which have characters in common which differentiate (q.v.) the unit (e.g. a geographic population, a genus, a family, an order) from other such units. A taxon encompasses all included taxa of lower rank (q.v.) and individual organisms. [...]"

Ranks

A taxon can be assigned a taxonomic rank, usually (but not necessarily) when it is given a formal name.

"Phylum" applies formally to any biological domain, but traditionally it was always used for animals, whereas "division" was traditionally often used for plants, fungi, etc.

A prefix is used to indicate a ranking of lesser importance. The prefix super- indicates a rank above, the prefix sub- indicates a rank below. In zoology, the prefix infra- indicates a rank below sub-. For instance, among the additional ranks of class are superclass, subclass and infraclass.

Rank is relative, and restricted to a particular systematic schema. For example, liverworts have been grouped, in various systems of classification, as a family, order, class, or division (phylum). The use of a narrow set of ranks is challenged by users of cladistics; for example, the mere 10 ranks traditionally used between animal families (governed by the International Code of Zoological Nomenclature (ICZN)) and animal phyla (usually the highest relevant rank in taxonomic work) often cannot adequately represent the evolutionary history as more about a lineage's phylogeny becomes known.

In addition, the class rank is quite often not an evolutionary but a phenetic or paraphyletic group and as opposed to those ranks governed by the ICZN (family-level, genus-level and species-level taxa), can usually not be made monophyletic by exchanging the taxa contained therein. This has given rise to phylogenetic taxonomy and the ongoing development of the PhyloCode, which has been proposed as a new alternative to replace Linnean classification and govern the application of names to clades. Many cladists do not see any need to depart from traditional nomenclature as governed by the ICZN, International Code of Nomenclature for algae, fungi, and plants, etc.

See also

  • Biology portal

Notes

  • The dictionary definition of taxon at Wiktionary

References

  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. 0429821352 ↩

  2. Magnol, Petrus (1689). Prodromus historiae generalis plantarum in quo familiae plantarum per tabulas disponuntur (in Latin). Montpellier: Pech. p. 79. https://books.google.com/books?id=RShVAAAAcAAJ&dq=Prodromus+historiae+generalis+plantarum+in+quo+familiae+plantarum+per+tabulas+disponuntur&pg=PA1 ↩

  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. https://gallica.bnf.fr/ark:/12148/btv1b8454361d/f9.item ↩

  4. Quammen, David (June 2007). "A Passion for Order". National Geographic Magazine. Archived from the original on August 27, 2008. Retrieved 27 April 2013. https://web.archive.org/web/20080827105848/http://ngm.nationalgeographic.com/print/2007/06/linnaeus-name-giver/david-quammen-text ↩

  5. This is not considered as mandatory, however, as indicated by terms for non-monophyletic groupings ("invertebrates", "conifers", "fish", etc). /wiki/Monophyly ↩

  6. 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. http://vertebrates.si.edu/herps/herps_pdfs/deQueiroz_pdfs/1990deQ_GauSZ.pdf ↩

  7. Romer, A. S. (1970) [1949]. The Vertebrate Body (4th ed.). W.B. Saunders. ↩

  8. Sylvain Adnet; Brigitte Senut; Thierry Tortosa; Romain Amiot, Julien Claude, Sébastien Clausen, Anne-Laure Decombeix, Vincent Fernandez, Grégoire Métais, Brigitte Meyer-Berthaud, Serge Muller (25 September 2013). Principes de paléontologie. Dunod. p. 122. ISBN 978-2-10-070313-5. La taxinomie s'enrichit avec l'invenition du mot «taxon» par Adolf Meyer-Abich, naturaliste allemand, dans sa Logik der morphologie, im Rahmen einer Logik der gesamten Biologie (1926) [Translation: Taxonomy is enriched by the invention of the word "taxon" by Adolf Meyer-Abich, German naturalist, in his Logik der morphologie, im Rahmen einer Logik der gesamten Biologie (1926).]{{cite book}}: CS1 maint: multiple names: authors list (link) 978-2-10-070313-5 ↩

  9. Meyer-Abich, Adolf (1926). Logik der Morphologie im Rahmen einer Logik der gesamten Biologie. Springer-Verlag. p. 127. ISBN 978-3-642-50733-5. {{cite book}}: ISBN / Date incompatibility (help) 978-3-642-50733-5 ↩

  10. Naik, V. N. (1984). Taxonomy of Angiosperms. New Delhi: Tata McGraw Hill. p. 2. /wiki/New_Delhi ↩

  11. ICZN (1999) International Code of Zoological Nomenclature. Glossary Archived 2005-01-03 at the Wayback Machine. International Commission on Zoological Nomenclature. http://www.iczn.org/iczn/index.jsp?booksection=glossary&nfv=true&mF= ↩