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Taxon - Wikipedia

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 African elephants form the genus Loxodonta,
name, its use is then governed by one of the nomenclature a widely accepted taxon.
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Linnaeus's system in Systema Naturae, 10th edition (1758),[4], as well as an unpublished work by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]

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".[7][8] For
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plants, it was proposed by Herman Johannes Lam in 1948, and it was adopted at the VII International
Botanical Congress, held in 1950.[9]

Definition
The glossary of the International Code of Zoological Nomenclature (1999) defines[10] 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 The hierarchy of
known. biological classification's
eight major taxonomic
In addition, the class rank is quite often not an evolutionary but a phenetic ranks. Intermediate
minor rankings are not
or paraphyletic group and as opposed to those ranks governed by the ICZN
shown.
(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

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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
ABCD Schema Biology portal
Alpha taxonomy
Chresonym
Cladistics
Folk taxonomy
Ichnotaxon
International Code of Nomenclature for algae, fungi, and plants
International Code of Nomenclature of Prokaryotes
International Code of Phylogenetic Nomenclature
International Code of Zoological Nomenclature (ICZN)
List of taxa named by anagrams
Rank (botany)
Rank (zoology)
Segregate (taxonomy)
Virus classification
Wastebasket taxon

Notes
1. This is not considered as mandatory, however, as indicated by terms for non-monophyletic
groupings ("invertebrates", "conifers", "fish", etc).

References
1. Cantino, Philip D.; de Queiroz, Kevin (2000). International Code of Phylogenetic Nomenclature
(PhyloCode): A Phylogenetic Code of Biological Nomenclature (https://www.routledge.com/Interna
tional-Code-of-Phylogenetic-Nomenclature-PhyloCode/Queiroz-Cantino/p/book/9781138332829).
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 (https://books.google.com/books?id=RShVAAAAcAAJ&dq=Prodromus+histori
ae+generalis+plantarum+in+quo+familiae+plantarum+per+tabulas+disponuntur&pg=PA1) (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] (https://gallica.bnf.fr/ark:/12148/btv1b8454
361d/f9.item). Paris: L’Imprimerie Royale. p. 562.
4. Quammen, David (June 2007). "A Passion for Order" (https://web.archive.org/web/200808271058
48/http://ngm.nationalgeographic.com/print/2007/06/linnaeus-name-giver/david-quammen-text).
National Geographic Magazine. Archived from the original (http://ngm.nationalgeographic.com/pri

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nt/2007/06/linnaeus-name-giver/david-quammen-text) 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" (http://vertebrates.si.edu/herps/herps_pdfs/deQueiroz_pdfs/1990deQ
_GauSZ.pdf) (PDF). Systematic Zoology. 39 (4): 307–322. doi:10.2307/2992353 (https://doi.org/1
0.2307%2F2992353). JSTOR 2992353 (https://www.jstor.org/stable/2992353).
6. Romer, A. S. (1970) [1949]. The Vertebrate Body (4th ed.). W.B. Saunders.
7. 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 (https://books.google.com/books?id=SUz
8AAAAQBAJ&pg=PA122). 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).]"
8. Meyer-Abich, Adolf (1926). Logik der Morphologie im Rahmen einer Logik der gesamten Biologie
(https://books.google.com/books?id=C8miBgAAQBAJ&pg=PA127). Springer-Verlag. p. 127.
ISBN 978-3-642-50733-5.
9. Naik, V. N. (1984). Taxonomy of Angiosperms. New Delhi: Tata McGraw Hill. p. 2.
10. ICZN (1999) International Code of Zoological Nomenclature. Glossary (http://www.iczn.org/iczn/in
dex.jsp?booksection=glossary&nfv=true&mF=) Archived (https://web.archive.org/web/2005010320
2015/http://www.iczn.org/iczn/index.jsp?booksection=glossary&nfv=true&mF=) 2005-01-03 at the
Wayback Machine. International Commission on Zoological Nomenclature.

External links
The dictionary definition of taxon at Wiktionary

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