Acanthocereus

Shrubs, erect to arching, clambering, or climbing, often sparingly branched, sometimes forming impenetrable thickets. Roots diffuse, adventitious where arching stems touch soil. Stems segmented or unsegmented, green, greatly elongate, angled, 30-400[-700] × (4-)6-10 cm; ribs 3-5[-7], narrowly triangular to winglike, very prominent, 3-5 cm deep, less than 1 cm thick, rib crests undulate; areoles widely spaced, located next to sinuses, 2-5 cm apart along ribs, circular to oval, short woolly. Spines [0-]4-10 per areole, diffusely spreading, brown or reddish [white, yellowish, or black], aging gray, ± straight, acicular to subulate, terete or somewhat flattened, longest spines 10-40[-70] mm, hard; radial spines [0-]6-8 per areole, 5-25 mm; central spines [0-]1-2[-4] per areole, 0-40 mm. Flowers nocturnal, lateral to terminal on stems 1 or more years old, at adaxial edge of areoles, funnelform, [11-]14-20[-25] cm; outer tepals green or purple tinged, lanceolate-linear, 3-5 × 1 cm; inner tepals white, broadly linear to narrowly oblanceolate, 5-15 × 1-4 cm, margins entire or minutely denticulate; ovary minutely scaly, spiny [spineless], with short wool; stigma lobes 10-15, white, to 12 mm. Fruits indehiscent or irregularly dehiscent longitudinally, red to red-purple, spheric, ovoid, ellipsoid, oblong, or pyriform, 30-80[-120] mm, fleshy or juicy [tough in A. columbianus], scaly, spiny [or spineless]; scales deciduous; pulp red; floral remnant persistent. Seeds black, broadly obovoid, to 4.8 mm, smooth and shiny; testa cells flat. x = 11.

Acanthocereus needs critical taxonomic study. E. F. Anderson (2001) followed W. Barthlott and D. R. Hunt (1993) in recognizing six species; other accounts have recognized up to twelve species or as few as two (A. tetragonus and A. occidentalis Britton & Rose).