Taxons

Taxon (plural taxa) is a unit of biological classification that groups together one or more populations sharing a set of characteristics and treated as a single unit for naming and study. A taxon may occupy any rank in the hierarchical system, from species and genus up to family, order, class, phylum (division), kingdom, and domain. The name of a taxon is its taxonomic name, governed by formal nomenclatural codes that aim to provide stable, unique names. Examples include the International Code of Zoological Nomenclature for animals and the International Code of Nomenclature for algae, fungi, and plants; bacteria and archaea follow related but distinct rules.

In practice, a taxon is defined by its circumscription (which organisms are included) and its composition; a type specimen anchors the name for a species. Taxes are used to reflect evolutionary relationships, but not all named groups are equally informative. A central concept is monophyly: a taxon that includes an ancestor and all its descendants (a clade). Some groups are paraphyletic or polyphyletic, containing only some descendants or aggregating unrelated lineages, which has led to revisions in classification.

Taxonomy and systematics are dynamic: new data, especially molecular phylogenetics, can alter the delimitation or rank of a taxon. The term taxon thus describes any formally recognized unit in classification, while taxon names function as labels that enable communication about organisms, databases, and research. Biodiversity informatics maintains records of taxa, their synonyms, and their circumscriptions to support data interoperability.