In biological classification, family (Latin: familia) is a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there's the option of an immediately lower rank, indicated by the prefix sub-: subfamily (Latin: subfamilia). a taxonomic unit, a taxon, in that rank. In that case the plural is families (Latin familiae) » :Example: "Walnuts and Hickories belong to t… (More on Subfamily)