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.
Examples
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 listed below.