Plants usually erect, ascending, sprawling, pendent, or decumbent, branched or unbranched, sometimes forming dense mounds to 500 branches, usually not deep-seated in substrate. Roots diffuse (usually a fascicle of several, tuberlike roots greatly exceeding stem diameter in E. poselgeri; sometimes adventitious in E. pentalophus). Stems unsegmented, yellow-green to dark green, spheric to long cylindric, sometimes tapering distally, (1-)2-70(-130)[-200] × (0.6-)1-15 cm, less than 40 cm at flowering, skin hard and brittle (less often soft), tuberculate (especially on immature plants) or ribbed; ribs 4-26, crests indistinctly to prominently undulate (irregularly notched or sharply folded if desiccated); areoles 1-52 mm apart along ribs, circular to linear, never completely confluent; cortex and pith soft, mucilaginous. Spines (0-)4-55 per areole, white, yellow, reddish, brown, or black, subulate or acicular to bristlelike, (0-)3-150 × 0.1-2.5 mm, hard, smooth or microscopically roughened (especially in E. triglochidiatus); radial spines (0-)4-38 (-45) per areole, straight or curved, sometimes pectinately arranged, (0-)2-40(-50) mm; central spines 0-17 per areole, straight, curved, or twisted, never hooked, terete, elliptic in cross section or variously angled to flattened. Flowers diurnal (a few species remaining open at night) [or nocturnal], bisexual (at least appearing so) or functionally unisexual, ± lateral on stem from year-old areoles (rarely terminal), broadly to narrowly funnelform or short tubular, 20-120 × (10-)15-150 mm; flower tube 5-26[-50] mm (measured from base of innermost tepals to base of nectar chamber); inner tepals pink, red, magenta, orange, yellow, brownish, or greenish (rarely white), proximally a darker or contrasting color or similar to distal portion; ovary smooth to tuberculate, scales usually minute, spines very prominent, areoles woolly; stigma lobes 5-22, green or yellowish green [rarely white or red]. Fruits indehiscent or dehiscent through short longitudinal slits, green, purplish brown, pink, or red, spheric to narrowly obovoid, usually 20-30 mm, juicy, drying quickly, scales minute; areoles spiny, spine clusters usually deciduous at maturity. Seeds black or dark reddish brown, spheric to obovoid, 0.8-2 mm, strongly tuberculate or rugose; testa cells strongly convex, sometimes irregularly confluent into ridges with interstitial pits. x = 11.
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