Shrubs, epiphytic or rarely epipetric, erect to pendent, many branched. Roots diffuse or adventitious along stems. Stems segmented, green, segments leaflike, narrowly elongate-oblanceolate, terete or 3-angled in narrow proximal portion, broadly flattened and bladelike distally, with prominent midvein-like axis, [30-]50-120+[-500] × [1.5-]4-5[-12+] cm, glabrous; ribs 2 or, on proximal portion and on juvenile stems, 3, rib margins (crests) crenate-undulate to shallow lobed [serrate to pinnatifid in other species]; areoles only in sinuses along rib margins (ca. 2-7 cm apart along rib), circular, woolly, stiff spines absent, sometimes fine, hairlike bristles present; areolar glands absent; cortex and pith mucilaginous. Spines usually absent from adult stems, present and slender on terete and juvenile stems. Flowers nocturnal [diurnal in 2 species], lateral on stem in marginal areoles, with long tube, salverform to funnelform, 8-38 cm; flower tube straight or strongly curved to 90°; outer tepals greenish [to yellow, white, or dull red] often tinged with red, 3-10 cm, margins entire; inner tepals white [to yellow], 3-10 cm, margins entire; ovary scaly, spineless, spiny, or with bristles or hairlike spines; scales small; stigma lobes 8-21, white, extending beyond stamens, ca. 10 mm. Fruits dehiscent along 1 side when mature, light green, red, or purple, smooth [to ridged or angular], ellipsoid to ovoid, [20-]40-100 × 20-50 mm, fleshy, spineless, spiny, or with bristles or hairlike spines; pulp white or slightly pinkish; floral remnant persistent. Seeds black, reniform, 2-3 × 1-2.5 mm; testa cells shiny or dull when minutely pitted. x = 11. The spineless, leaflike stems of this epiphytic genus make it easy to overlook as a member of Cactaceae. The usually white, nocturnal flowers with long, thin flower tubes, copious nectar, and strong fragrance suggest hawkmoth pollinators for most species.