taxón

A taxon, plural taxa, is a unit in biological classification that groups one or more populations of organisms judged to form a coherent unit by their shared characteristics and genetic relatedness, and that is given a formal scientific name. The concept is used across the tree of life and applies at any rank in the Linnaean system, from species and genus to family, order, class, phylum, kingdom, and domain.

Circumscription and membership of a taxon are not fixed; different researchers may circumscribe a taxon differently, and new data can alter its composition. Modern taxonomy often aims for monophyletic groups, i.e., taxa that include an ancestor and all its descendants, while paraphyletic and polyphyletic taxa are discussed in some classifications.

Nomenclature for taxa is governed by codes appropriate to the group: the ICZN for animals, the ICN for plants, algae, and fungi, and separate codes for bacteria. A taxon's name is its formal label and may have synonyms—historical names no longer in active use. The naming system is designed to be stable and uniquely identifiable.

Taxa can be recognized at various ranks, with species being the fundamental unit in many biological contexts. Examples include Homo sapiens (species), Homo (genus), Hominidae (family), and Primates (order). The term taxon also encompasses informal groupings and taxonomic opinions that reflect current understanding of evolutionary relationships.

Etymology traces back to Greek taxis, meaning arrangement or ranking, reflecting the purpose of taxa as units arranged within hierarchical classification.