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{{CompPsy}}
 
{{CompPsy}}
 
{{Biological classification}}
 
{{Biological classification}}
A '''taxon''' (plural '''taxa'''), or '''taxonomic unit''', is a name designating an organism or group of [[organism]]s. In biological nomenclature according to Carl Linnaeus, a taxon is assigned a [[taxonomic rank]] and can be placed at a particular level in a systematic hierarchy reflecting evolutionary relationships.
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[[image:Elephants_in_Kenya.jpg||thumb|270px|All the [[elephants]] together are a taxon]]
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A '''taxon''' (''plural:'' '''taxa''') is a group (of one or more) of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a taxonomic group is done by a taxonomist. It is not uncommon for one taxonomist to disagree with another on what exactly belongs to a taxon, or on what exact criteria should be used for inclusion. Taxonomists sometimes make a distinction between "good" (or natural) taxa and others that are "not good" (or artificial). Today it is common to define a good taxon as one that reflects presumptive evolutionary (phylogenetic) relationships, but this too is not in itself a requirement.
   
A distinction is to be made between taxa/taxonomy and classification/systematics. The former refers to biological names and the rules of naming. The latter refers to rank ordering of taxa according to presumptive evolutionary (phylogenetic) relationships.
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The Glossary of the '''''[[International Code of Zoological Nomenclature]]''''' (1999) defines a
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*"taxon, (pl. taxa), n.
   
Note: "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.
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::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. [...]"
   
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But there are other definitions. A taxon may be given a formal name, a scientific name. Such a scientific name is governed by one of the [[Nomenclature Codes]], which sets out rules to determine which scientific name is correct for that particular grouping.
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== Ranks ==
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A taxon can be assigned a rank, usually (but not necessarily) when it is given a formal name. The rank of a given taxon is not necessarily fixed, but can be altered later by another (or the same) taxonomist.
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  +
"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.
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{{Biological classification}}
 
A simple [[mnemonic|mnemonic phrase]] to remember the sequence of taxonomic levels is:
 
A simple [[mnemonic|mnemonic phrase]] to remember the sequence of taxonomic levels is:
"Dignified Kings Play Chess On Fine Green Silk"; another, highly expedient example is "King Philip's Class Orders the Family Genius to Speak".
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"Dignified Kings Play Chess On Fine Green Silk"; another, highly expedient example is "King Philip's Class Orders the Family Genius to Speak" or "Dumb King Philip Crawled Over Five Girl Scouts" or "King Phillip Came Over From Germany Stoned" or "Keep Pots Clean Or Family Gets Sick."
   
 
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:
 
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:
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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 [[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]]al and [[paraphyletic]] group and as opposed to those ranks governed by the ICZN, 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 is to govern the application of taxa to [[clade]]s.
 
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 [[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]]al and [[paraphyletic]] group and as opposed to those ranks governed by the ICZN, 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 is to govern the application of taxa to [[clade]]s.
   
==See also==
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==See also==
 
*[[Alpha taxonomy]]
 
*[[Alpha taxonomy]]
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*[[Folk taxonomy]]
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*[[Chresonym]]
 
*[[Cladistics]]
 
*[[Cladistics]]
 
*[[ICBN]]
 
*[[ICBN]]
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*[[Rank (zoology)]]
 
*[[Rank (zoology)]]
 
*[[Segregate (taxonomy)]]
 
*[[Segregate (taxonomy)]]
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== References ==
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{{reflist}}
   
 
[[Category:Scientific classification]]
 
[[Category:Scientific classification]]
 
[[Category:Zoological nomenclature]]
 
[[Category:Zoological nomenclature]]
 
[[Category:Botanical nomenclature]]
 
[[Category:Botanical nomenclature]]
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{{Link FA|de}}
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[[he:טקסון]]
 
[[he:טקסון]]
 
[[lt:Taksonas]]
 
[[lt:Taksonas]]
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[[hu:Taxon]]
 
[[mt:Takson]]
 
[[mt:Takson]]
 
[[nl:Taxon]]
 
[[nl:Taxon]]
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[[pt:Táxon]]
 
[[pt:Táxon]]
 
[[ru:Таксон]]
 
[[ru:Таксон]]
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[[stq:Taxon]]
 
[[simple:Taxon]]
 
[[simple:Taxon]]
 
[[sk:Taxón]]
 
[[sk:Taxón]]
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[[sl:Takson]]
 
[[fi:Taksoni]]
 
[[fi:Taksoni]]
 
[[sv:Taxon]]
 
[[sv:Taxon]]

Latest revision as of 10:24, April 2, 2009

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Biological classification L PengoSpeciesGenusFamilyOrderClassPhylumKingdomDomainLife

Error: image is invalid or non-existent

The hierarchy of biological classification's major eight taxonomic ranks. Intermediate minor rankings are not shown.
File:Elephants in Kenya.jpg

A taxon (plural: taxa) is a group (of one or more) of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a taxonomic group is done by a taxonomist. It is not uncommon for one taxonomist to disagree with another on what exactly belongs to a taxon, or on what exact criteria should be used for inclusion. Taxonomists sometimes make a distinction between "good" (or natural) taxa and others that are "not good" (or artificial). Today it is common to define a good taxon as one that reflects presumptive evolutionary (phylogenetic) relationships, but this too is not in itself a requirement.

The Glossary of the International Code of Zoological Nomenclature (1999) defines 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. [...]"

But there are other definitions. A taxon may be given a formal name, a scientific name. Such a scientific name is governed by one of the Nomenclature Codes, which sets out rules to determine which scientific name is correct for that particular grouping.

Ranks Edit

A taxon can be assigned a rank, usually (but not necessarily) when it is given a formal name. The rank of a given taxon is not necessarily fixed, but can be altered later by another (or the same) taxonomist.

"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.

Biological classification L PengoSpeciesGenusFamilyOrderClassPhylumKingdomDomainLife

Error: image is invalid or non-existent

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

A simple mnemonic phrase to remember the sequence of taxonomic levels is: "Dignified Kings Play Chess On Fine Green Silk"; another, highly expedient example is "King Philip's Class Orders the Family Genius to Speak" or "Dumb King Philip Crawled Over Five Girl Scouts" or "King Phillip Came Over From Germany Stoned" or "Keep Pots Clean Or Family Gets Sick."

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:

Superclass
Class
Subclass
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 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 phenetical and paraphyletic group and as opposed to those ranks governed by the ICZN, 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 is to govern the application of taxa to clades.

See alsoEdit

References Edit

<span class="FA" id="de" style="display:none;" />


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