A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). Once named, a taxon will usually have a rank and can be placed at a particular level in a hierarchy.

A broad scheme of ranks in hierarchical order:

Domain

Kingdom

Phylum (animals or plants) or Division (plants)

Class

Order

Family

Genus

Species

Subspecies

A simple mnemonic phrase to remember the order is "King Philip Came Over From Great Spain". Alternatively "Domineering King Phillip Can Order Five Green Shirts". Also, "Keep Putting Cream On Fred's Glasses Sam" or "Dumb King Phillip Chases Old Fat Girl Scouts". In biology, a domain (also superregnum, superkingdom, or empire) is the top-level grouping of organisms in scientific classification, higher than a kingdom. ... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen). ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... This article discusses categorisations of organisms. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... In biological classification, family (Latin: familia, plural familiae) is 1) a rank or 2) a taxon in that rank. ... In biology, a genus (plural genera) is a taxonomic grouping. ... In biology, a species is one of the basic units of biodiversity. ... In zoology, as in other branches of biology, subspecies is the rank immediately subordinate to a species. ... A mnemonic (pronounced in Received Pronunciation) is a memory aid, and most serve as an educational related purpose. ...

A prefix is used to indicate a ranking of lesser importance. The prefix super- indicates a rank above, the prefix sub- indicates a rank below. In zoology the prefix infra- indicates a rank below sub-. For instance:

Superclass

Class

Subclass

Infraclass

Do note that rank is relative, and restricted to the particular scheme used. For example, liverworts have been grouped, in various systems of classification, as a family, order, or a class. The use of ranks is challenged by users of cladistics and has led to the PhyloCode being proposed. ... This cladogram shows the relationship among various insect groups. ... Types of Clade (Note: Stem-based is now branch-based, to avoid confusion with the term stem group which means total clade minus crown clade.) The PhyloCode is a developing draft for a formal set of rules governing phylogenetic nomenclature. ...

See also

• Alpha taxonomy
• Cladistics
• Rank (botany)
• Rank (zoology)
• Segregate (taxonomy)

Taxonomy, sometimes alpha taxonomy, is the science of finding, describing and naming organisms, thus giving rise to taxa. ... This cladogram shows the relationship among various insect groups. ... In botanical nomenclature, a taxon is usually assigned to a rank in a hierarchy. ... In zoology, a taxon is usually assigned to a rank in a hierarchy. ... In Taxonomy, a segregate, or a segregate taxon is a created when a taxon is divided into several more specific taxa. ...