Genus

A genus groups together species that are closely related through descent from a recent common ancestor, sitting one rank above species. When a genus contains only a single species, it is called a monotypic genus — the textbook's example is the red panda, whose genus Ailurus contains only the one species, Ailurus fulgens, a reddish-brown, cat-sized mammal native to the eastern Himalayas.

When a genus instead contains several closely related species, it is called a polytypic genus. The textbook's example is the genus Felis (cats), which includes several distinct species such as Felis domestica (the domestic cat), Felis margarita (the jungle cat, though the text's spelling here is imprecise) and Felis silvestris (the wild cat). The contrast between Ailurus (one species) and Felis (many species) shows that the genus rank can vary enormously …