monotypic

Describing any taxon that includes only one subordinate taxon. Thus a family with just one genus or a genus with a single species, are examples of monotypic taxa. An extreme case of monotypy occurs in the classification of the maidenhair tree, Ginkgo biloba. This species is the sole representative of the genus Ginkgo, the family Ginkgoaceae, and the order Ginkgoales - each being monotypic taxa.