Autor: (Berger) Riccobono

“Hairy Cereus” referring to the character of the floral tube, which is hairy in this genus.
A genus of shrubby to treelike plants, creeping, decumbent to erect (some rare species are pendulous) or massive columnar, reaching up to 15 m high. Ribs straight, with areoles close-set, covered with wool, with usually distinct radial and central spines, variable in size and thickness, finely aciculate to strongly subulate, according to species.
Flowers nocturnal or diurnal, large, funnel-shaped and widely open, with long and sturdy floral tube, fleshy, scaly, more or less densely covered with dark brown (rarely white) hairs borne at the axil of scales, with greenish, pinkish or reddish outer tepals and white, yellow, red, or purple pink inner tepals, with numerous stamens and with pistil stigmas elongated and also numerous, pollinated, according to species, by bees (Apis mellifera, Arhysosage ochracea, Augochloropsis sp., Bombus opifex, Brachyglossula ancasti, B. communis, B. martinezi, Caenohalictus sp., Centris nigerrima, Lasioglossum sp., Megachile saulcyi, Ptilothrix tricolor, Trichoturgus sp., Trigona spinipes, Xylocopa grisescens, X. ordinaria, X. splendidula), wasps (Allosclrtetica lanosa, Polybia ruficeps), flies (Copestylum concinna), beetles (Arctodium vulpinus, Lichnia gallardoi), hummingbirds (Adelomyia melanogenys, Heliomaster squamosus, Patagona gigas, Rhodopis vesper) during the day; or Sphingideae (Manduca diffissa) and bats (Glossophaga soricina, Lonchophylla mordax) at night. Fruits thick-walled, globose greenish to reddish, with hairs but without spines, pulp white, longitudinally dehiscent, not always retaining the remains of the dried perianth. Seeds rather small, globose to elongated, numerous, dark brown to black, pitted or foveolate, dispersal essentially myrmecophilous (Solenopsis sp.), also ornithophilous (Mimus thenca) and chiropterophilous (Glossophaga soricina).
The genus Trichocereus has a very wide distribution area, and grows on various substrates, usually grassy and rocky or sandy, ferruginous soils, in deserts, in mountains of the Andes, on rocky hillsides, on dry plains, drainage areas, canyons, sometimes clinging on cliff faces, or even living on saline soils, among bushes and xerophytic spiny shrubs, from 25 m (T. chiiensis subsp. litoralis) up to 4300 m in altitude, where some species withstand snow and frost.
Argentina (Buenos Aires, Catamarca, Cordoba, Jujuy, La Pampa, La Rioja, Mendoza, Salta, San Juan, San Luis, Santiago del Estero, Tucuman), Bolivia (Chuquisaca, Cochabamba, La Paz, Oruro, Potosi, Santa Cruz, Tarija), Chile (Antofagasta, Atacama, Coquimbo, Santiago, Valparaiso), Ecuador (Azuay, Loja), Paraguay (Concepcion), Peru (Ancash, Arequipa, Cuzco, Lima, Moquegua, Piura, Tacna).

Currently 43 recognised species (+ 6 subspecies and varieties):
– Trichocereus andalgalensis* (F.A.C.Weber) Hosseus 1939 (= T. huascha var. rubriflorus)
– Trichocereus angelesiae* R.Kiesling 1978
– Trichocereus arboricola* Kimnach 1990
– Trichocereus atacamensis* (Philippi) W.T.Marshall & Bock 1941
– Trichocereus atacamensis subsp. pasacana* (F.A.C.Weber ex RLimpler) Ritter 1980
– Trichocereus bertramianus* Backeb. 1935
– Trichocereus bolligerianus (Machler & Helmut Walter) S. Albesiano 2012
– Trichocereus bridgesii* (Salm-Dyck) Britton & Rose 1920 (ex E. lageniformis)
– Trichocereus cabrerae R.Kiesling 1976 (probable hybr.)
– Trichocereus camarguensis Cardenas 1953
– Trichocereus candicans* (Gillies ex Salm-Dyck) Britton & Rose 1920
– Trichocereus candicans subsp. pseudocandicans (Backeb.) J.Lode 2013
– Trichocereus caulescens Ritter 1966
– Trichocereus chalaensis Rauh & Backeb. 1956
– Trichocereus chiloensis* (Colla) Britton & Rose 1920
– Trichocereus chiloensis subsp. litoralis (Johow) Faundez 2007
– Trichocereus crassicaulis* (R. Kiesling) J. Lode 2013
– Trichocereus cuzcoensis Britton & Rose 1920
– Trichocereus deserticola* (Werderm.) Looser 1929
– Trichocereus hahnianus* (Backeberg) Guiggi 2013
– Trichocereus huascha* (F.A.C.Weber) Britton & Rose 1920
– Trichocereus huascha subsp. robusta* (Rausch) J.Lode 2013 (ex T. lobivioides)
– Trichocereus lamprochlorus* (Lem.) Britton & Rose 1920
– Trichocereus macrogonus* (Salm-Dyck) Riccob. 1909
– Trichocereus macrogonus var. pachanoi* (Britton & Rose) S.AIbesiano & R.Kiesling 2012 (= ex T. pachanoi)
– Trichocereus macrogonus subsp. peruvianus* (Britton & Rose) J.Lode 2013
– Trichocereus purpureopilosus Weingart 1930
– Trichocereus rowleyi* Friedrich 1974 (ex Lobivia grandiflora)
– Trichocereus quadratiumbonatus Ritter 1980
– Trichocereus schickendantzii* (F.A.C.Weber) Britton & Rose 1920
– Trichocereus schoenii Rauh & Backeb. 1958
– Trichocereus serpentinus (M.Lowry & M.Mendoza) J.Lode 2013
– Trichocereus skottsbergii* Backeb. 1950
– Trichocereus smrzianus* (Backeb.) Backeb. 1966
– Trichocereus spachianus (Lem.) Riccob. 1909
– Trichocereus spinibarbis* (Otto) F.Ritter 1965 ? (doubtful name)
– Trichocereus strigosus* (Salm-Dyck) Britton & Rose 1920
– Trichocereus tacaquirensls* Cardenas 1953
– Trichocereus taquimbalensis* Cardenas 1953
– Trichocereus tarijensis* (Vaupel) Werderm. 1940 (= T. poco)
– Trichocereus terscheckii* (Parm.) Britton & Rose 1920
– Trichocereus thelegonoides* (Speg.) Britton & Rose 1920
– Trichocereus thelegonus* (Weber) Britton & Rose 1920
– Trichocereus tunariensis Cardenas 1959
– Trichocereus vasquezii* Rausch 1974
– Trichocereus vatteri R.Kiesling 1976
– Trichocereus vollianus* Backeb. 1935
– Trichocereus walteri* Kiesling) J.G.Lambert 1998
– Trichocereus werdermannianus Backeb. 1935 (= T. validus)
Modifications proposed by S. Albesiano (2012):
– Trichocereus chiloensis subsp. australis (Ritter) Albesiano 2012
– Trichocereus chiloensis subsp. eburneus (Phil, ex K. Schum.) Albesiano 2012
– Trichocereus chiloensis subsp. panhoplites (K. Schum.) Albesiano 2012
– Trichocereus faundezii Albesiano 2012
– Trichocereus nigripilis (Phil.) Backeb. 1935 (ex T. coquimbanus)
– Trichocereus pectiniferus Albesiano 2012
– Trichocereus undulosus Albesiano 2012
– Trichocereus uyupampensis Backeberg 1936 (= T. glaucus)

References: "TAXONOMY of the CACTACEAE" -  ISBN 978-84-617-3692-8 (Vol. 2)