Autor: (Engelmann) F. Knuth

“Cylindrical Opuntia”, referring to the cylindrical shape of the stems in this genus, in contrast to Platyopuntia, or Opuntia, whose stems, or articles, are flattened.
A genus of much-branched, shrubby or treelike plants, of indeterminate growth. Stems and segments cylindrical or clavate, often and easily becoming loose, mostly tuberculate and of various length. Areoles with glochids. Spines of variable length, enclosed in a papery sheath soon falling.
Flowers diurnal, mostly self-sterile, well opened, of variable colours, yellow to greenish yellow, red, bronze or magenta, pollinated by bees (Apis, Bombus, Megachile, Xylocopa) and by hummingbirds (Archilochus alexandri, Calothorax lucifer, Calypte costae, Cynanthus latirostris), possibly by ants (Crematogaster opuntiae); the pollination by the wind (anemophily) is also a means of fertilization in some species (eg. C. echinocarpa). Fruits dry or fleshy, globose to
subglobose, sometimes davate, sometimes proliferating and forming a chain. Seeds rather large, flattened, suborbicular, straw-coloured, sometimes absent in fruits.
The genus Cylindropuntia is part of a plant community including several other cacti and succulents, and grows in a variety of habitats, sometimes forming densely populated colonies, among bushes and shrubs, on gravelly, sandy, sedimentary or volcanic soils, in mountainous or desert region, rocky escarpments, in valleys and arid outwash plains, on plateaus and hill slopes, in arroyos, drainage basins and depressions, on sandbars and gravel, from sea level up to 2100 min altitude, sometimes in regions covered with snow in winter (Colorado plateau), but also according to species, tropical dry scrub near the coast (Carribbean islands). Some species easily hybridize in nature.
The Antilles, Cuba, Haiti, Mexico (Aguascalientes, Baja California, Chihuahua, Coahuila, Colima, Durango, Guanajuato, Hidalgo, Mexico City DF, Michoacan, Nuevo Leon, Puebla, Queretaro, San Luis Potosi, Sinaloa, Sonora, Tamaulipas, Tlaxcala, Zacatecas…), Dominican Republic, Trinidad and Tobago, USA (Arizona, California, Colorado, Kansas, Nevada, New Mexico, Oklahoma, Texas, Utah), Venezuela. Note that Cylindropuntia tunicata is naturalized in Argentina, in Bolivia, in Chile, in Ecuador and in Peru, as well as C. rosea, where we can find it in Peru up to 3300 m in altitude.

Currently 34 recognised species + 9 subspecies, + several natural hybrids among which 3 examples are presented here:
– Cylindropuntia abyssi (Hester) Backeb. 1958
– Cylindropuntia acanthocarpa* (Engelm. & Bigelow) F.M.Knuth 1935
– Cylindropuntia acanthocarpa subsp. coloradensis (L.D.Benson) u.Guzman 2003
– Cylindropuntia acanthocarpa subsp. major (Engelm.) U.Guzman 2003
– Cylindropuntia acanthocarpa subsp. thornberi (Thornber & Bonker) J.Lode 2013
– Cylindropuntia alcahes* (F.A.C.Weber) F.M.Knuth 1935
– Cylindropuntia alcahes subsp. burrageana (Britton & Rose) U.Guzman 2003
– Cylindropuntia anteojoensis* (Pinkava) E.F.Anderson 2000
– Cylindropuntia arbuscula* (Engelm.) F.M.Knuth 1935
– Cylindropuntia bigelovii (Engelm.) F.M.Knuth 1935
– Cylindropuntia bigelovii subsp. ciribe (Engelm. ex J.M.Coulter) U.Guzman 2003
– Cylindropuntia californica* (Torn & A.Gray) F.M.Knuth 1935
– Cylindropuntia californica subsp. parkeri (Coulter) U.Guzman 2003
– Cylindropuntia californica subsp. rosarica (G.E.Linds.) U.Guzman 2003
– Cylindropuntia calmalliana (J.M.Coult.) F.M.Knuth 1935
– Cylindropuntia caribaea* (Britton & Rose) F.M.Knuth 1935
– Cylindropuntia cholla* (F.A.C.Weber) F.M.Knuth 1935
– Cylindropuntia davisii (Engelm. & Bigelow) F.M.Knuth 1935
– Cylindropuntia echinocarpa* (Engelm. & Bigelow) F.M.Knuth 1935
– Cylindropuntia fulgida* (Engelm.) F.M.Knuth 1935
– Cylindropuntia ganderi* (c.B.Wolf) Rebman 2001
– Cylindropuntia ganderi subsp. catavinensis (Rebman) U.Guzman 2003
– Cylindropuntia hystrix (Grisebach) Areces Mallea 1976
– Cylindropuntia imbricata* (Haw.) F.M.Knuth 1935
– Cylindropuntia kleiniae* (DC.) F.M.Knuth 1935
– Cylindropuntia leptocaulis* (DC.) F.M.Knuth 1935
– Cylindropuntia lindsayi* (Rebman) Rebman 2001
– Cylindropuntia molesta* (Brandegee) F.M.Knuth 1935
– Cylindropuntia molesta subsp. clavellina (Engelm.) U.Guzman 2003
– Cylindropuntia munzii* (C.B.Wolf) Backeb. 1966 (possible hybrid)
– Cylindropuntia prolifera* (Engelm.) F.M.Knuth 1935
– Cylindropuntia ramosissima* (Engelm.) F.M.Knuth 1935
– Cylindropuntia rosea* (DC.) Backeb. 1958
– Cylindropuntia sanfelipensis* (Rebman) Rebman 2001
– Cylindropuntia santamaria (E M.Baxter) Rebman 2001
– Cylindropuntia spinosior* (Engelm.) F.M.Knuth 1935
– Cylindropuntia tesajo* (Engelm.) F.M.Knuth 1935
– Cylindropuntia thurberi* (Engelm.) F.M.Knuth 1935
– Cylindropuntia tunicata* (Lehm.) F.M.Knuth 1935
– Cylindropuntia versicolor* (Engelm. ex J.M.Coulter) F.M.Knuth 1935
– Cylindropuntia whipplei* (Engelm. & Bigelow) F.M.Knuth 1935
– Cylindropuntia wigginsii (L.D.Benson) Robinson 1973
– Cylindropuntia wolfii* (L.D.Benson) Rebman 2001
– Cylindropuntia X multigeniculata* (Clokey) Backeb. 1958
– Cylindropuntia X tetracantha* (Tourney) F.M.Knuth 1935
– Cylindropuntia X viridiflora (Britton & Rose) F.M.Knuth 1935

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