A taxon (plural taxa) is an element of a taxonomy, e.g. in the scientific classification in biology. For example, in biology, the family Hominidae is one taxon, as is the genus Homo and the species Homo sapiens.
Taxa form a hierarchical scheme, each being broken down into subtaxa.
In traditional Linnaean taxonomy, taxa are ranked as follows, with some of the less widely used ranks indented:
- Kingdom
- Phylum (animals) or Division (plants)
- Class
- Order
- Family
- Tribe
- Genus
- Section
- Series
- Species
- Variety
- form
A prefix is used to indicate a ranking that falls between two taxa. The prefix super- indicates a rank above another, the prefix sub- indicates a rank below another, and the prefix infra- indicates a rank below sub-. For instance:
- Superclass
- Class
- Subclass
- Infraclass
It has become generally accepted that taxa should contain an ancestral form and all or some of its descendants, though the validity of the latter category is increasingly debated.
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