Autor: Britton & Rose

“Fierce Cactus” referring to the size and robustness of the spines in this genus.
A genus of plants usually massive, solitary or branched, globose flattened to elongated, cylindrical or barrel-shaped, with apex depressed. Ribs well defined, variable in number, areoles rather large, having nectariferous glands. Radial and central spines well separated, the latter generally very strong, sometimes ringed and hooked.
Flowers diurnal, self-sterile, appearing around the apex, funnel-shaped to bell-shaped, yellow, greenish yellow, orange, red, magenta, pink, purple, rarely white, with floral tube bearing scales and unarmed areoles, pollinated by bees, in particular those specializing in cacti such as Diadasia opuntiae, D. rinconis, Idiomelissodes (Svastra) duplocincta (Apidae), Ashmeadiella opuntiae, Lithurge apicalis (Megachilidae), but also Apis, Augochlorella, Bombus, Halictus,
Lasioglossum, Megachile, Xylocopa…. Fruits globose to elongated, thick-walled, dry or juicy when ripe, with basal or irregular dehiscence, or indehiscent. Seeds variable in size, matt or smooth and shiny, dark brown to black, papillose or reticulate. Dispersion of seeds ensured by lizards and small mammals.
The genus Ferocactus has a wide geographic distribution between Mexico and the United States, and grows in mostly arid areas, usually on well drained limestone, clayey or gravelly rocky soils, granitic or volcanic slopes, in canyons, on plateaus, in deserts, sandy plains, valleys, alluvial areas, also in grasslands, arroyos, coastal plains and low hills, from sea level (F. herrerae) up to 3000 m in altitude. It is also found on some islands of Baja California, where one of the endemic species is the biggest of all the genus, reaching up to 4 m high (F. diguettii), sometimes on only one island
(F. johnstonianus found in the island Angel de la Guarda). The genus grows mostly among shrubs, together with other cacti, Bromeliads and succulents, and is often the dominant plant of the landscape. The climates can be very different: humid, warm and arid, mountainous and cold.
Mexico (Aguascalientes, Baja-California, Chihuahua, Coahuila, Colima, Durango, Guanajuato, Hidalgo, Jalisco, Mexico D.F., Michoacan, Morelos, Nuevo Leon, Oaxaca, Puebla, Queretaro, San Luis Potosi, Sinaloa, Sonora, Tamaulipas, Veracruz, Zacatecas), USA (Arizona, California, Nevada, New Mexico, Texas, Utah).

Currently 26 recognised species, although some conflicting, plus 14 subspecies:
– Ferocactus acanthodes* (Lem.) Britton & Rose 1922 (= F. cylindraceus)
– Ferocactus acanthodes subsp. eastwoodiae (Benson) J.Lode 2013
– Ferocactus alamosanus* (Britton & Rose) Britton & Rose 1922
– Ferocactus alamosanus subsp. reppenhagenii* (G.Unger) N.P.Taylor 1998
– Ferocactus chrysacanthus* (Orcutt) Britton & Rose 1922
– Ferocactus chrysacanthus subsp. grandiflorus* (G.E.Lindsay) N.P.Taylor 1998
– Ferocactus diguetii* (F.A.C.Weber) Britton & Rose 1922
– Ferocactus echidne* (DC.) Britton & Rose 1922
– Ferocactus emoryi* (Engelm.) Orcutt 1926
– Ferocactus emoryi subsp. rectispinus* (Engelm.) N.P.Taylor 1998
– Ferocactus flavovirens* (Scheidw.) Britton & Rose 1922
– Ferocactus fordii* (Orcutt) Britton & Rose 1922
– Ferocactus fordii subsp. borealis N.P.Taylor 2002
– Ferocactus glaucescens* (DC.) Britton & Rose 1922
– Ferocactus gracilis* H.E.Gates 1933
– Ferocactus gracilis subsp. coloratus (H.E.Gates) N.P.Taylor 1998
– Ferocactus gracilis subsp. gatesii (G.E.Lindsay) N.P.Taylor 1998
– Ferocactus gracilis subsp. tortulispinus* (H.E.Gates) J.Lode 2013
– Ferocactus haematacanthus* (Salm-Dyck) Bravo ex Backeb. & F.M.Knuth 1935
– Ferocactus herrerae* J.G.Ortega 1927
– Ferocactus histrix* (DC.) G.E.Linds. 1955
– Ferocactus johnstonianus* Britton & Rose 1923
– Ferocactus lapistinus* (Haw.) Britton & Rose 1922
– Ferocactus latispinus subsp. greenwoodii (Glass) N.P.Taylor 2005
– Ferocactus latispinus subsp. spiralis* (Karw. ex Pfeiffer) N.P.Taylor 1998 (= F. recurvus)
– Ferocactus lindsayi* Bravo 1966
– Ferocactus macrodiscus* (Mart.) Britton & Rose 1922
– Ferocactus peninsulae* (F.A.C.Weber) Britton & Rose 1922
– Ferocactus pilosus* (Galeotti ex Salm-Dyck) Werderm. 1933
– Ferocactus pottsii* (Salm-Dyck) Backeb. 1961
– Ferocactus robustus* (Pfeiff.) Britton & Rose 1922
– Ferocactus santa-maria* Britton & Rose 1922
– Ferocactus schwarzii* G.E.Lindsay 1955
– Ferocactus townsendianus* Britton & Rose 1922
– Ferocactus viridescens* (Torr. & A.Gray) Britton & Rose 1922
– Ferocactus viridescens subsp. littoralis (G.E.Linds.) F.Wolf & R.Wolf 2004
– Ferocactus wislizenii* (Engelm.) Britton & Rose 1922
– Ferocactus wislizenii subsp. ajoensis R.Fencl & R.Kalas 2013
– Ferocactus wislizenii subsp. tiburonensis (G.E.Linds.) Pilbeam & Bowdery 2005

References: "TAXONOMY of the CACTACEAE" -  ISBN 978-84-617-3723-9 (Vol. 1)