Biological Classification - Taxonomic Ranks

Taxonomic Ranks

A classification as defined above is hierarchical. In a biological classification, rank is the level (the relative position) in a hierarchy. (Rarely, the term "taxonomic category" is used instead of rank.) The International Code of Zoological Nomenclature defines rank, in the nomenclatural sense, as:

The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g., all families are for nomenclatural purposes at the same rank, which lies between superfamily and subfamily).

There are seven main ranks defined by the international nomenclature codes: kingdom, phylum/division, class, order, family, genus, species. "Domain", a level above kingdom, has become popular in recent years, but has not been accepted into the codes. Ranks between the seven main ones can be produced by adding prefixes such as "super-", "sub-" or "infra-". Thus a subclass has a rank between class and order, a superfamily between order and family. There are slightly different ranks for zoology and for botany, including subdivisions such as tribe.

Ranks are somewhat arbitrary, but hope to encapsulate the diversity contained within a group—a rough measure of the number of diversifications that the group has been through.