The taxonomy of Ferocactus pilosus is still muddled. Over time there have been 3 names applied to apparently 1 species. Sometime in 1845, Frederic Stains, who was an official with a mining company in San Luis Potosi, sent a large specimen to Kew Gardens, and although the plant was referred to as Ferocactus stainsii, it was never officially described or validly published. In 1850, Ferocactus pilosus was given a full description by Salm-Dyck based on a plant supplied by Galeotti from somewhere in Mexico. At this point F. stainsii is relegated to synonymy under F. pilosus. The third name, Ferocactus pringlei was based on material collected by Pringle in Coahuila and differs by having more distinct ribs with areoles more widely separated, more numerous, duller colored spines and white hair-like bristles. These characters are considered within the range of variation by many botanists, thereby lumping two seemingly distinct taxa into one.