In traditional Linnaean taxonomy, taxa are ranked as follows, with some of the less widely used ranks indented:
- Phylum (animals) or Division (plants)
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:
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.