Smallest category in a kingdom

From large to small, taxonomic categories are kingdom (let's say Animalia), phylum (Chordata), class (Mammalia), order (Primates), family (Hominidae), genus (Homo), and species (Homo sapiens, for example). There are also subphyla, subclasses etc., tribes falling into families, and races falling into species (for example Homo sapiens neanderthalensis, Neanderthal man, and Homo sapiens sapiens, being us; both are the same species but different races). So, race would be the smallest, though even smaller categories sometimes apply to domestic and arteficially selected animals and plants (breeds, crops).