A monotypic taxon is a taxon that has only one immediately subordinate subtaxon.
A genus is said to be monotypic if it only includes one species. This species is therefore the type of its genus. Such a genus is then said to be unispecific or monospecific. Similarly, a species is said to be monotypic if it has no subspecies. In general, only one holotype has been established. A family with only one genus, such as the Nepenthaceae or the Chionididae, is also said to be monotypic or, more precisely, monogeneric.
Note: as classifications are constantly evolving, the examples below may not all be monotypic taxa at this time.
the species Actophilornis africanus is monotypic because without any subspecies.
monospecific genera (or unispecific):
Chamaerops, monospecific genus because it only includes the dwarf palm.
Achimenantha, monospecific genus: it includes the single species Achimenantha naegelioides
examples of higher ranks:
the subfamily Aeluroscalabotinae and the genus Aeluroscalabotes are monotypic (and monospecific), with a single species, Aeluroscalabotes felinus.
the order Amborellales is monotypic, as is the family Amborellaceae, which admits only one genus, Amborella, itself monospecific with Amborella trichopoda as the only admitted species.
the order Selaginellales is monotypic, as is the family Selaginellaceae which now only admits one genus: Selaginella.
By contrast, a taxon that includes several sub-taxa is called “polytypic”.
Example of a polytypic taxon:
Ginkgo, with its only living species Ginkgo biloba, appears monotypic. But in fact, there are many fossil species of Ginkgo: Ginkgo is therefore polytypic.
monothetic Botany portal Zoology portal