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{{short description|Group of one or more populations of an organism or organisms which have distinguishing characteristics in common}}
{{Short description|Grouping of biological populations}}
{{about||the journal|Taxon (journal)|other uses|Taxa (disambiguation)}}
{{for multi|the journal|Taxon (journal)|other uses|Taxa (disambiguation)}}


[[File:Elephants in Kenya.jpg|thumb|270px|[[African elephant]]s form the [[genus]] ''Loxodonta'', a widely accepted taxon.]]
[[File:Elephants in Kenya.jpg|thumb|270px|[[African elephant]]s form the [[genus]] ''Loxodonta'', a widely accepted taxon.]]


In [[biology]], a '''taxon''' ([[back-formation]] from ''[[Taxonomy (biology)|taxonomy]]''; plural '''taxa''') is a group of one or more populations of an organism or organisms seen by [[Taxonomy (biology)|taxonomists]] to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular [[Taxonomic rank|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. 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.
In [[biology]], a '''taxon''' ([[back-formation]] from ''[[Taxonomy (biology)|taxonomy]]''; plural '''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 [[Taxonomic rank|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. 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 set forth in [[Carl Linnaeus|Linnaeus]]'s system in ''[[Systema Naturae]]'', 10th edition (1758),<!--
Initial attempts at classifying and ordering organisms (plants and animals) were set forth in [[Carl Linnaeus]]'s [[Linnaean taxonomy|system]] in ''[[Systema Naturae]]'', 10th edition (1758),<!--
--><ref>{{cite web |last=Quammen |first=David |title=A Passion for Order |publisher=National Geographic Magazine |date=June 2007 |url=http://ngm.nationalgeographic.com/print/2007/06/linnaeus-name-giver/david-quammen-text |access-date=27 April 2013}}</ref><!--ENDRef--> as well as an unpublished work by [[Bernard de Jussieu|Bernard]] and [[Antoine Laurent de Jussieu]]. 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'', of [[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 [[Phylogenetics|evolutionary relationships]].{{NoteTag|This is not considered as mandatory, however, as indicated by terms for non-[[Monophyly|monophyletic]] groupings ("invertebrates", "conifers", "fish", etc).}}
--><ref>{{cite web |last=Quammen |first=David |title=A Passion for Order |publisher=National Geographic Magazine |date=June 2007 |url=http://ngm.nationalgeographic.com/print/2007/06/linnaeus-name-giver/david-quammen-text |access-date=27 April 2013}}</ref><!--ENDRef--> as well as an unpublished work by [[Bernard de Jussieu|Bernard]] and [[Antoine Laurent de Jussieu]]. 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, [[Systematics|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 [[Phylogenetics|evolutionary relationships]].{{NoteTag|This is not considered as mandatory, however, as indicated by terms for non-[[Monophyly|monophyletic]] groupings ("invertebrates", "conifers", "fish", etc).}}


Many modern systematists, such as advocates of [[phylogenetic nomenclature]], use [[Cladistics|cladistic]] methods that require taxa to be [[Monophyly|monophyletic]] (all descendants of some ancestor). Their basic unit, therefore, the [[clade]] is equivalent to the taxon, assuming that taxa should reflect evolutionary relationships. Similarly, among those contemporary taxonomists working with the traditional [[Binomial nomenclature|Linnean (binomial) nomenclature]], few propose taxa they know to be [[Paraphyly|paraphyletic]].<ref>{{cite journal |title=Phylogeny as a Central Principle in Taxonomy: Phylogenetic Definitions of Taxon Names |author=de Queiroz, K & J Gauthier |journal=Systematic Zoology |volume=39 |issue=4 |year=1990 |pages=307–322 |url=http://vertebrates.si.edu/herps/herps_pdfs/deQueiroz_pdfs/1990deQ_GauSZ.pdf |doi=10.2307/2992353 |jstor=2992353}}</ref> An example of a well-established taxon that is not also a clade is the [[Class (biology)|class]] [[Reptile|Reptilia]], the reptiles; birds are descendants of reptiles but are not included in the Reptilia{{citation needed|date=July 2021}} (birds are included in the Aves).
Many modern systematists, such as advocates of [[phylogenetic nomenclature]], use [[Cladistics|cladistic]] methods that require taxa to be [[Monophyly|monophyletic]] (all descendants of some ancestor). Their basic unit, therefore, 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 [[Paraphyly|paraphyletic]].<ref>{{cite journal |title=Phylogeny as a Central Principle in Taxonomy: Phylogenetic Definitions of Taxon Names |author=de Queiroz, K & J Gauthier |journal=Systematic Zoology |volume=39 |issue=4 |year=1990 |pages=307–322 |url=http://vertebrates.si.edu/herps/herps_pdfs/deQueiroz_pdfs/1990deQ_GauSZ.pdf |doi=10.2307/2992353 |jstor=2992353}}</ref> An example of a long-established taxon that is not also a clade is the [[Class (biology)|class]] [[Reptile|Reptilia]], the reptiles; birds and mammals are the descendants of animals traditionally classed as reptiles, but neither are included in the Reptilia (birds are traditionally placed in the class [[Bird|Aves]], and mammals in the class [[Mammal|Mammalia]]).<ref name=Romer>{{cite book |last=Romer |first=A. S. |orig-year=1949 |title=The Vertebrate Body |publisher=W.B. Saunders |year=1970 |edition=4th <--|pages=-->}}</ref>


== History ==
== History ==
The term ''taxon'' was first used in 1926 by [[:de:Adolf Meyer-Abich|Adolf Meyer-Abich]] for animal groups, as a backformation from the word [[Taxonomy (biology)|Taxonomy]]; the word ''Taxonomy'' had been coined a century before from the Greek components ''[[wiktionary:τάξις|τάξις]]'' ([[taxis]], meaning arrangement) and ''[[wiktionary:νόμος|-νομία]]'' ([[:wikt:-nomy|-nomia]] meaning [[Scientific method|method]]).<ref name="AdnetSenut2013">{{cite book |author1= Sylvain Adnet |author2= Brigitte Senut |author3= Thierry Tortosa |author4= Romain Amiot, Julien Claude, Sébastien Clausen, Anne-Laure Decombeix, Vincent Fernandez, Grégoire Métais, Brigitte Meyer-Berthaud, Serge Muller |title= Principes de paléontologie |url= https://books.google.com/books?id=SUz8AAAAQBAJ&pg=PA122|date=25 September 2013|publisher=Dunod|isbn=978-2-10-070313-5|pages=122|quote=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).]}}</ref><ref name="Meyer">{{cite book|last=Meyer-Abich|first=Adolf|title=Logik der Morphologie im Rahmen einer Logik der gesamten Biologie|url=https://books.google.com/books?id=C8miBgAAQBAJ&pg=PA127|year=1926|publisher=Springer-Verlag|isbn=978-3-642-50733-5|page=127}}</ref> For plants, it was proposed by [[Herman Johannes Lam]] in 1948, and it was adopted at the VII [[International Botanical Congress]], held in 1950.<ref>Naik, V. N. (1984). Taxonomy of Angiosperms. Tata McGraw Hill, New Delhi, p. 2.</ref>
The term ''taxon'' was first used in 1926 by [[:de:Adolf Meyer-Abich|Adolf Meyer-Abich]] for animal groups, as a back-formation from the word [[Taxonomy (biology)|taxonomy]]; the word ''taxonomy'' had been coined a century before from the Greek components ''[[wiktionary:τάξις|τάξις]]'' (''taxis'', meaning arrangement) and ''[[wiktionary:νόμος|-νομία]]'' ([[:wikt:-nomy|''-nomia'']] meaning [[Scientific method|method]]).<ref name="AdnetSenut2013">{{cite book |author1=Sylvain Adnet |url=https://books.google.com/books?id=SUz8AAAAQBAJ&pg=PA122 |title=Principes de paléontologie |author2=[[Brigitte Senut]] |author3=Thierry Tortosa |author4=Romain Amiot, Julien Claude, Sébastien Clausen, Anne-Laure Decombeix, Vincent Fernandez, Grégoire Métais, Brigitte Meyer-Berthaud, Serge Muller |date=25 September 2013 |publisher=Dunod |isbn=978-2-10-070313-5 |pages=122 |quote=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).]}}</ref><ref name="Meyer">{{cite book|last=Meyer-Abich|first=Adolf|title=Logik der Morphologie im Rahmen einer Logik der gesamten Biologie|url=https://books.google.com/books?id=C8miBgAAQBAJ&pg=PA127|year=1926|publisher=Springer-Verlag|isbn=978-3-642-50733-5|page=127}}</ref> For plants, it was proposed by [[Herman Johannes Lam]] in 1948, and it was adopted at the VII [[International Botanical Congress]], held in 1950.<ref>Naik, V. N. (1984). Taxonomy of Angiosperms. Tata McGraw Hill, New Delhi, p. 2.</ref>


== Definition ==
== Definition ==
The Glossary of the ''[[International Code of Zoological Nomenclature]]'' (1999) defines<ref>ICZN (1999) [http://www.iczn.org/iczn/index.jsp?booksection=glossary&nfv=true&mF= International Code of Zoological Nomenclature. Glossary]. International Commission on Zoological Nomenclature.</ref> a
The glossary of the ''[[International Code of Zoological Nomenclature]]'' (1999) defines<ref>ICZN (1999) [http://www.iczn.org/iczn/index.jsp?booksection=glossary&nfv=true&mF= International Code of Zoological Nomenclature. Glossary] {{Webarchive|url=https://web.archive.org/web/20050103202015/http://www.iczn.org/iczn/index.jsp?booksection=glossary&nfv=true&mF= |date=2005-01-03 }}. International Commission on Zoological Nomenclature.</ref> a
*"taxon, (pl. taxa), n.
*"taxon, (pl. taxa), n.


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A taxon can be assigned a [[taxonomic rank]], usually (but not necessarily) when it is given a formal name.
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 (biology)|domain]], but traditionally it was always used for animals, whereas "Division" was traditionally often used for [[plant]]s, [[fungus|fungi]], etc.
"[[Phylum]]" applies formally to any biological [[domain (biology)|domain]], but traditionally it was always used for animals, whereas "division" was traditionally often used for [[plant]]s, [[fungus|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 (biology)|class]] are superclass, subclass and infraclass.
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 (biology)|class]] are superclass, subclass and infraclass.


Rank is relative, and restricted to a particular systematic schema. For example, [[Marchantiophyta|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.
Rank is relative, and restricted to a particular systematic schema. For example, [[Marchantiophyta|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 [[Special:WhatLinksHere/International Code of Zoological Nomenclature|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 [[clade]]s. 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|ICN]], etc.
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 [[clade]]s. 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 ==
== See also ==
{{Portal|Biology}}
* [[ABCD Schema]]
* [[ABCD Schema]]
* [[Alpha taxonomy]]
* [[Alpha taxonomy]]
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== Notes ==
== Notes ==
{{NoteFoot}}
{{NoteFoot}}
{{reflist|group=note}}


== References ==
== References ==

Revision as of 14:09, 9 January 2023

African elephants form the genus Loxodonta, a widely accepted taxon.

In biology, a taxon (back-formation from taxonomy; plural 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. 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 set forth in Carl Linnaeus's system in Systema Naturae, 10th edition (1758),[1] as well as an unpublished work by Bernard and Antoine Laurent de Jussieu. 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). Their basic unit, therefore, 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.[2] 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 are included in the Reptilia (birds are traditionally placed in the class Aves, and mammals in the class Mammalia).[3]

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 (taxis, meaning arrangement) and -νομία (-nomia meaning method).[4][5] For plants, it was proposed by Herman Johannes Lam in 1948, and it was adopted at the VII International Botanical Congress, held in 1950.[6]

Definition

The glossary of the International Code of Zoological Nomenclature (1999) defines[7] 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

LifeDomainKingdomPhylumClassOrderFamilyGenusSpecies
The hierarchy of biological classification's eight major taxonomic ranks. Intermediate minor rankings are not shown.

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

Notes

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

References

  1. ^ Quammen, David (June 2007). "A Passion for Order". National Geographic Magazine. Retrieved 27 April 2013.
  2. ^ 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.
  3. ^ Romer, A. S. (1970) [1949]. The Vertebrate Body (4th <-- ed.). W.B. Saunders. pp. -->.
  4. ^ 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)
  5. ^ Meyer-Abich, Adolf (1926). Logik der Morphologie im Rahmen einer Logik der gesamten Biologie. Springer-Verlag. p. 127. ISBN 978-3-642-50733-5.
  6. ^ Naik, V. N. (1984). Taxonomy of Angiosperms. Tata McGraw Hill, New Delhi, p. 2.
  7. ^ ICZN (1999) International Code of Zoological Nomenclature. Glossary Archived 2005-01-03 at the Wayback Machine. International Commission on Zoological Nomenclature.

External links

  • The dictionary definition of taxon at Wiktionary