Endangered species is recognized: as a species identified to be under threat of extinction or expiration. In the United States, the US Fish and Wildlife Service maintains an official list of species that are considered endangered and threatened or of special concern. Internationally, the International Union for the Conservation of Nature (IUCN) maintains listings of more than 49,000 species, subspecies and varieties of flora and fauna and places each in a category based on the level of threats that species is facing in the wild.