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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, Development ...

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 Greek: ) includes the study o ...
, 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 Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classifica ...
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 binomi ...

Linnaeus
's system in ''
Systema Naturae ' (originally in Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic ...
'', 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 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 ...
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 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, ...
, 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 In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
(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 organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

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 (; ) is the movement Movement may refer to: Common uses * Movement (clockwork), the internal mechanism of a timepiece * Motion (physics), commonly referred to as movement Arts, entertainment, and media Literature * Movement ...

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 Veendam () is a town and Municipalities of the Netherlands, municipality with a population of 27,752 in the province of Groningen (province), Groningen in the northeast of the Netherlands. A Holland ...
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 in that rules the formal of treated as s. It is also informally known as the ICZN Code, for its publisher, the (which shares the acronym "ICZN"). The rules princi ...
'' (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, taxonomic rank is the relative level of a group of organisms (a taxon) in a Taxonomy (biology), taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family (biology), family, order (biology), order, ...
, 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 Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s,
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

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 plant, non-vascular embryophyte, land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plan ...
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, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared ch ...

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 Convention may refer to: * Convention (norm), a custom or tradition, a standard of presentation or conduct ** Treaty, an agreement in international law * C ...
) 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 A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree (graph theory), tree showing the evolutionary relationships among va ...

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, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

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 organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

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, 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: ...
* Chresonym *
Cladistics Cladistics (; ) is an approach to biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared ch ...

Cladistics
*
Folk taxonomy A folk taxonomy is a vernacular name, naming system, as distinct from Taxonomy (general), scientific taxonomy. Folk biological classification is the way people traditionally describe and organize their natural surroundings/the world around them, ...
*
Ichnotaxon An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an Artifact (archaeology), artifact. ''Ichnotaxa'' comes from the Greek (language), Greek ίχνος, ''ichnos'' meaning ''t ...
*
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 name A botanical name is a formal scientific name Science (from the Latin Latin (, ...
* 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