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In
biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, Developmenta ...

biology
, a taxon (
back-formation In etymology, back-formation is the process of creating a new lexeme by removing actual or supposed affixes.Crystal, David. ''A Dictionary of Linguistics and Phonetics, Sixth Edition'', Blackwell Publishers, 2008. The resulting neologism is called ...
from ''
taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
''; plural taxa) is a group of one or more populations of an organism or organisms seen by
taxonomists In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
to form a unit. Although neither is required, a taxon is usually known by a particular name and given a particular
ranking A ranking is a relationship between a set of items such that, for any two items, the first is either "ranked higher than", "ranked lower than" or "ranked equal to" the second. In mathematics Mathematics (from Ancient Greek, Greek: ) include ...
, 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 In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...
, 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
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomia ...
's system in ''
Systema Naturae ' (originally in Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...
'', 10th edition (1758), as well as an unpublished work by
Bernard Bernard ('' Bernhard'') is a French and West Germanic masculine given name. The name is attested from at least the 9th century. West Germanic ''Bernhard'' is composed from the two elements ''bern'' "bear" and ''hard'' "brave, hardy". Its native ...

Bernard
and
Antoine Laurent de Jussieu Antoine Laurent de Jussieu (; 12 April 1748 – 17 September 1836) was a France, French botanist, notable as the first to publish a natural classification of flowering plants; much of his system remains in use today. His classification was bas ...

Antoine Laurent de Jussieu
. The idea of a unit-based system of
biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxon, taxa (singular: ...
was first made widely available in 1805 in the introduction of
Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fu ...

Jean-Baptiste Lamarck
's ''Flore françoise'', of
Augustin Pyramus de Candolle Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 September 1841) was a Swiss people, Swiss botany, botanist. René Louiche Desfontaines launched de Candolle's botanical career by recommending him at an herbarium. Within a couple ...
'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
evolutionary relationships
. Many modern systematists, such as advocates of
phylogenetic nomenclature Phylogenetic nomenclature is a method of nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal naming ...
, use
cladistic Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...

cladistic
methods that require taxa to be
monophyletic 300px, A cladogram of the primates, showing a ''monophyletic'' taxon: ''the simians'' (in yellow); a ''paraphyletic'' taxon: ''the prosimians'' (in cyan, including the red patch); and a ''polyphyletic'' group: ''the night-active primates, i.e., ...
(all descendants of some ancestor). Their basic unit, therefore, the
clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell t ...

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 In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—Monophyly, monophyletic subgroups. The group is said to be paraphyleti ...
. An example of a well-established taxon that is not also a clade is the
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
Reptilia Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids ...

Reptilia
, the reptiles; birds are descendants of reptiles but are not included in the Reptilia (birds are included in the Aves).


History

The term ''taxon'' was first used in 1926 by Adolf Meyer-Abich for animal groups, as a backformation from the word
Taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
; the word ''Taxonomy'' had been coined a century before from the Greek components '' τάξις'' (
taxis A taxis (plural taxes , ) is the movement of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It ...

taxis
, meaning arrangement) and '' -νομία'' ( -nomia meaning
method Method ( grc, μέθοδος, methodos) literally means a pursuit of knowledge, investigation, mode of prosecuting such inquiry, or system. In recent centuries it more often means a prescribed process for completing a task. It may refer to: *Scient ...

method
). For plants, it was proposed by
Herman Johannes Lam Herman Johannes Lam (3 January 1892 in Veendam – 15 February 1977 in Leiden) was a Dutch people, Dutch botany, botanist. Lam studied at Utrecht University, where he was awarded a Doctor of Biology in 1919. Lam was the appointed the director of th ...
in 1948, and it was adopted at the VII
International Botanical Congress International Botanical Congress (IBC) is an international meeting of botanist Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist ...
, held in 1950.


Definition

The Glossary of the ''
International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention Convention may refer to: * Convention (norm), a custom or tradition, a standard of presentation or conduct ** Treaty, an agreement in international law * Co ...
'' (1999) definesICZN (1999
International Code of Zoological Nomenclature. Glossary
International Commission on Zoological Nomenclature.
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 In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, ...
, usually (but not necessarily) when it is given a formal name. "Phylum" applies formally to any biological
domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function *Doma ...
, but traditionally it was always used for animals, whereas "Division" was traditionally often used for
plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions o ...

plant
s,
fungi A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as ...

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 Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
are superclass, subclass and infraclass. Rank is relative, and restricted to a particular systematic schema. For example,
liverworts The Marchantiophyta () are a division of non-vascular land plant The Embryophyta () or land plants are the most familiar group of green plants that form vegetation on earth. Embryophyta is a clade within the Phragmoplastophyta, a larger clade ...
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 Cladistics (; ) is an approach to biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

cladistics
; for example, the mere 10 ranks traditionally used between animal families (governed by the
ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is also informally known as the IC ...
) 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 , based on completely sequenced genomes. A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolution ...

phylogeny
becomes known. In addition, the class rank is quite often not an evolutionary but a
phenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
or
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—Monophyly, monophyletic subgroups. The group is said to be paraphyleti ...

paraphyletic
group and as opposed to those ranks governed by the ICZN (family-level, genus-level and
species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

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 The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the g ...
'', which has been proposed as a new alternative to replace Linnean classification and govern the application of names to
clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell t ...

clade
s. Many cladists do not see any need to depart from traditional nomenclature as governed by the ICZN, ICN, etc.


See also

* ABCD Schema *
Alpha taxonomy In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
* Chresonym *
Cladistics Cladistics (; ) is an approach to biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular ...

Cladistics
*
Folk taxonomy A folk taxonomy is a vernacular A vernacular or vernacular language refers to the language or dialect that is spoken by people that are inhabiting a particular country or region. The vernacular is typically the native language A first lang ...
*
Ichnotaxon An ichnotaxon (plural ichnotaxa) is "a taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inte ...
*
International Code of Nomenclature for algae, fungi, and plants The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all those "tradi ...
* International Code of Zoological Nomenclature (ICZN) *
List of taxa named by anagrams In the biological nomenclature codes, an anagram An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. For example, the word ''anagram'' itself ...
*
Rank (botany) In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grou ...
*
Rank (zoology) In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grou ...
*
Segregate (taxonomy)In Alpha taxonomy, taxonomy, a segregate, or a segregate taxon is created when a taxon is split off from another taxon. This other taxon will be better known, usually bigger, and will continue to exist, even after the segregate taxon has been split o ...
*
Virus classification Virus classification is the process of naming viruses and placing them into a Alpha taxonomy, taxonomic system similar to the classification systems used for cell (biology), cellular organisms. Viruses are classified by phenotypic characteristics, ...
The scientific term used for these categories is taxa(taxon-singular)


Notes


References


External links

* {{Authority control Biological classification Botanical nomenclature Zoological nomenclature