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Shrubs, erect, arching or climbing (not in Australia). Roots diffuse, adventitious where arching stems touch soil, or napiform or tuber-like and clustered. Stems segmented or not, monomorphic or dimorphic, often greatly elongate, young stems 3–10-angled or ribbed, adult stems with 3–5 ribs or ridges, sometimes cylindric (not in Australia), rarely flattened (not in Australia), or sometimes wavy (not in Australia); areoles 2–5 cm apart along ribs, circular to oval, short-woolly; spines short or long, (0–) 4–10 per areole, radial and central spines similar. Flowers lateral to terminal on stems, nocturnal, often fragrant. Perianth infundibuliform or tubular-infundibuliform, usually opening widely, white; pericarpel and hypanthium bearing triangular scale leaves with small spines or bristles; petaloid lobes narrowly obovate, spreading. Fruit globose, ovoid, ellipsoid (in Australia) to pyriform, sometimes tuberculate, fleshy, spiny or spineless, dehiscent or indehiscent, withered perianth persistent; pulp red. Seeds broad-oval, to 4.8 mm long, 1.2–3.3 mm diam., glossy black or black-brown, sometimes minutely reticulate-papillate; hilum oblique.
Succulent erect or clambering shrubs; stems phylloid and jointed, the joints elongate, rooting adventitiously at the tips, 3-to 5-angled, the areoles marginal on the angles, shortly pubescent and prominently spiny. Leaves very inconspicuous, acicular and fugacious or apparently wholly lacking. Flowers nocturnal, sessile, borne singly at the areoles; perianth large, subsalverform, with an elongate tube, the segments very numerous, the outer progressively shorter and narrower than the inner, widely spreading, the tube bearing several minute caducous bracts and prominent pubescent and spiny areoles; stamens very numerous, the filaments somewhat shorter than the perianth, united at progressively deeper levels to the hypanthium; ovary cylindric-ovoid, the areoles numerous and crowded, pubescent and spiny; style filiform, terete, somewhat shorter than the outer and upper stamens. Fruit a fleshy berry with numerous seeds.
