Taxon

Definition

A group of organisms that a taxonomist judges to constitute a coherent biological unit, formally recognized with a name and rank in a classification system. A taxon may be a monotypic population or encompass multiple populations, species, or higher groupings; it exists as a conceptual entity rather than a physical object, though it is anchored to actual specimens or observations through type specimens and circumscription.

Etymology

From Greek taxis (arrangement, order) + -on (neuter suffix), coined in the 1920s to replace vaguer terms like 'group' or 'unit' in formal taxonomy.

Example

The wolf spider genus Hogna is a taxon ranked at the genus level within the family Lycosidae; its constituent species (each also a taxon) share diagnostic genitalic and eye-arrangement characters that distinguish them from related genera.

Synonyms

• taxonomic unit
• taxonomic group

Related Terms

• taxonomic rank
• clade
• monophyly
• Type specimen
• circumscription
• Nomenclature
• Phylogenetic tree
• operational taxonomic unit

Usage Notes

Plural 'taxa' is mandatory in scientific writing; 'taxons' is nonstandard. The term applies to named entities at any rank (subspecies to kingdom) and to unnamed candidate species awaiting formal description. Contrast with 'OTU' (operational taxonomic unit), which denotes a provisional cluster from molecular data without formal nomenclatural status. A taxon is not the same as a taxonomic name: the name is the label, while the taxon is the biological concept being labeled.