The genus Mammillaria is one of the largest in the cactus family (Cactaceae), with currently 171 known species and varieties recognized[citation needed]. Most of the mammillarias are native to Mexico, but some come from the southwest USA, the Caribbean, Colombia, Venezuela, Guatemala and Honduras.
The first was described by Carolus Linnaeus as Cactus mammillaris in 1753, deriving name from Latin mammilla, "nipple", referring to the tubercles that are one of the plant's specific features. In 1812, the cactus specialist Adrian Haworth described the genus Mammillaria to contain this and related species. Numerous species are commonly known as nipple cactus, fishhook cactus or pincushion though such terms may also be used for related taxa, namely Escobaria
Mammillarias have extremely variable spination from species to species, and attractive flowers, making them specifically attractive for cactus hobbyists. Most mammillarias plants are considered easy to cultivate, though some species are among the hardest cacti to grow. Several taxa are threatened with extinction at least in the wild, due to habitat destruction and especially overcollecting for the pot plant trade. Cactus fanciers can assist conservation of these rare plants by choosing nursery-bred specimens (wild-collected ones are illegal to possess for the rarest species anyways). Besides helping to preserve rare plants, one can gain experience in growing and breeding cacti in general with nursery-bred rare mammillarias: several mammillarias are quite easy (for cacti) to grow from seeds. One such species, popular and widely available from nursery stock but Endangered in the wild, is Mammillaria zeilmanniana.
