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A taxon (plural: taxa) or taxonomic unit is a name designating an organism or a group of organism
Organism

In biology, an organism is any life thing . In at least some form, all organisms are capable of response to stimulus , reproduction, growth and developmental biology, and maintenance of homeostasis as a stable whole....
s. In biological nomenclature according to Carl Linnaeus, a taxon is assigned a taxonomic rank
Taxonomic rank

Taxonomic rank, taxonomic category, rank, or category is an abstract term used in the scientific classification, or taxonomy, of organisms....
 and can be placed at a particular level in a systematic hierarchy reflecting evolutionary relationships.

A distinction is to be made between taxa/taxonomy and classification/systematics. The former refers to biological names and the rules of naming.






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A taxon (plural: taxa) or taxonomic unit is a name designating an organism or a group of organism
Organism

In biology, an organism is any life thing . In at least some form, all organisms are capable of response to stimulus , reproduction, growth and developmental biology, and maintenance of homeostasis as a stable whole....
s. In biological nomenclature according to Carl Linnaeus, a taxon is assigned a taxonomic rank
Taxonomic rank

Taxonomic rank, taxonomic category, rank, or category is an abstract term used in the scientific classification, or taxonomy, of organisms....
 and can be placed at a particular level in a systematic hierarchy reflecting evolutionary relationships.

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.

Note: "Phylum" applies formally to any biological domain
Domain (biology)

In Biology taxonomy, a domain is the highest taxonomic rank of organisms, higher than a Kingdom . According to the three-domain system of Carl Woese, introduced in 1990, the Tree of life consists of three domains: Archaea, Bacteria and Eukaryota....
, but traditionally it was always used for animals, whereas "Division" was traditionally often used for plant
Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
s, fungi
Fungus

A fungus is a Eukaryote organism that is a member of the Kingdom Fungi . The fungi are a monophyletic group, also called the Eumycota , that is phylogeny distinct from the morphologically similar slime molds and water molds ....
, etc.

A simple mnemonic phrase
Mnemonic

A mnemonic device is a memory aid. Commonly met mnemonics are often verbal, something such as a very short poem or a special word used to help a person remember something, particularly lists, but may be visual, kinesthetic or auditory....
 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
Class (biology)

A class is the taxonomic rank in the biological classification of organisms in biology below phylum and above Order .The orders of taxonomy are life, Domain , kingdom , phylum, class , order , family , genus, and species....
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
Cladistics

Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic systems because it focuses on evolution rather than similarities between species, and because it places heavy emphasis on objective, quantitative analysis....
; for example, the mere 10 ranks traditionally used between animal families (governed by the ICZN
ICZN

ICZN may refer to:*International Commission on Zoological Nomenclature, an organization*International Code of Zoological Nomenclature, published by that organization...
) 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
PhyloCode

The International Code of Phylogenetic Nomenclature, known for short as the PhyloCode, is a developing draft for a formal set of rules governing phylogenetic nomenclature....
, which is to govern the application of taxa to clade
Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
s.

See also

  • Alpha taxonomy
    Alpha taxonomy

    Alpha taxonomy is the science of finding, describing and categorising organisms, thus leading to the recognition of proposed taxonomic groups, or taxon , which may then be naming conventions....
  • Folk taxonomy
    Folk taxonomy

    A folk taxonomy is a vernacular name, and can be contrasted with taxonomy. Folk biological classification is the way peoples make sense of and organize their natural surroundings/the world around them, typically making generous use of form taxa like "shrubs", "bug s", "ducks", "ungulates" and the likes....
  • Chresonym
    Chresonym

    The term Chresonym is derived from the Greek language "chresis" and refers to the "use" of a name. In biodiversity informatics, a chresonym refers to the use of a taxon name, usually a species name, within a publication....
  • Cladistics
    Cladistics

    Cladistics is the hierarchical classification of species based on evolutionary ancestry. Cladistics is distinguished from other taxonomic systems because it focuses on evolution rather than similarities between species, and because it places heavy emphasis on objective, quantitative analysis....
  • ICBN
  • ICZN
    ICZN

    ICZN may refer to:*International Commission on Zoological Nomenclature, an organization*International Code of Zoological Nomenclature, published by that organization...
  • Rank (botany)
  • Rank (zoology)
  • Segregate (taxonomy)
    Segregate (taxonomy)

    In Alpha 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 off....