Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
species, specie (nn.)
Species is both singular and plural: He thinks this plant is a different species. These species are difficult to tell apart. Specie, a back-formation singular, has been around since the eighteenth century, but it is Nonstandard for all biological and general meanings; species is the Standard term. The specialized word specie, meaning “coin, hard currency,” is a regular singular English mass noun.
