; Syn. Pl. Succ. 177 (1812) s. str.
Distribution: Tropical America from SW-USA and Mexico to Colombia and Venezuela, West Indies. The genus is here taken s. str. fide de Vos et al. (2025). It contains numerous superflous split names and garden forms
= Cactus L.; Sp. Pl. [Linnaeus] 1: 468 (1753), nom. rej.
= Cryptocarpocactus Guiggi; Cactology 5(Suppl. 15): 10 (2024)
= Dolichothele (Lem.) Britton & Rose; Cactaceae [Britton & Rose] 4: 61 (1923)
= Ebnerella Buxb.; Oesterr. Bot. Z. 98: 88 (1951)
= Escobariopsis Doweld; Sukkulenty (Moscow) 3(1-2): 23 (2000)
= Fimbriatocactus Guiggi; Cactology 5(Suppl. 14): 4 (2023)
= Haagea Frič; Zivot v Prírod 29(36-37) Kakt. a Succ. 69 (1925), nom. illeg.
= Krainzia Backeb.; Blätt. Kakteenf. 1938(6): 211 (1938)
= Lactomamillaria Frič; Českoslov. Zahradn. Listy 133 (1924), nom. illeg.
= Leptocladia Buxb.; Oesterr. Bot. Z. 98: 82 (1951)
= Leptocladodia Buxb.; Oesterr. Bot. Z. 101: 601 (1954)
= Mamillopsis (É.Morren) F.A.C.Weber ex Britton & Rose; Cactaceae [Britton & Rose] 4: 19 (1923)
= Mammariella Shafer; Bull. New York Bot. Gard. 13: 139 (1913)
= Melocactus Boehm.; Def. Gen. Pl., ed. 3: 79 (1760), nom. rej.
= Neomammillaria Britton & Rose; Cactaceae [Britton & Rose] 4: 65 (1923)
= Porfiria Boed.; Z. Sukkulentenk. 2: 210 (1926)
= Pseudomammillaria Buxb.; Bot. Stud. 12: 84 (1951)
= Solisia Britton & Rose; Cactaceae [Britton & Rose] 4: 64 (1923)