In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. Although the phrase appears to indicate that a taxon has a single type specimen (with no syntypes, lectotypes, or other types) and no heterotypic/junior synonyms, that is not the usage.
A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispecific" is sometimes preferred.
In botanical nomenclature, a monotypic genus is a genus in the special case where a genus and a single species are simultaneously described.
In contrast an oligotypic taxon contains more than one but only a very few subordinate taxa.
Just as the term monotypic is used to describe a large taxon including only one subdivision, one can also refer to the contained taxon as monotypic within the larger taxon, e.g. a genus monotypic within a family. Some examples of monotypic groups are:
- The family Cephalotaceae includes only one genus, Cephalotus, and only one species, Cephalotus follicularis – the Albany pitcher plant.
- The hyacinth macaw (Anodorhynchus hyacinthinus) is a monotypic species; no subspecies have been distinguished within the species.
- The bearded reedling (Panurus biarmicus) has a few subspecies across its range, but belongs to the genus Panurus, which current knowledge considers monotypic (the only genus) within the family Panuridae.
- The cream-spotted cardinalfish (Ozichthys albimaculosus), found in tropical Australia and southern New Guinea, is the type species of the monotypic genus Ozichthys.
- The flowering plant Breonadia salicina is the only species in the monotypic genus Breonadia.