Taxon (source code)
= Taxon
= Taxa
{synonym}
A <taxon> is a group of <organisms> recognized as a unit in <taxonomy (biology)>. A <taxonomic rank> specifies a position in the classification hierarchy; a <taxon> is the particular group placed there. Thus <Felidae> is a <taxon> at the rank of <taxonomic family>, while <Carnivora> is a <taxon> at the rank of <taxonomic order>.<Biology 2e by Mary Ann Clark and others>[section 20.1, Classification Levels and Figure 20.6]{ref}
One <organism> can belong to many nested <taxa>. Membership in a <species>, its <genus (biology)> and its <taxonomic family> describes different levels of the same classification. A rank alone does not identify the group: the word family could refer to many distinct <taxa>.
For a constructed information-system example, let a family contain genera A and B, with three and five recognized species respectively. A species record can store its species identifier and follow parent relationships to recover its genus and family. If a later classification moves one species from A to B, the family's species total remains eight, while the genus totals change from 3 and 5 to 2 and 6. Group membership and the name of the rank are separate pieces of information.
A <clade> is specifically a group containing an ancestor and all its descendants. Calling a group a <taxon> does not by itself establish that it is a <clade>; that claim depends on its circumscription and the inferred <phylogenetic tree>.<Biology 2e by Mary Ann Clark and others>[section 20.1, Phylogenetic Trees and classification]{ref}
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