Plants unbranched or few branched, deep-seated in substrate or rising 1-15 cm above substrate. Roots appearing as taproots at soil surface, branching, and ultimately diffuse. Stems unsegmented, green or gray-green, obconic-cylindric to spheric or depressed-spheric, 2-15 × 1-15 cm; tubercles distinct, not confluent into ribs, pyramidal, conic, truncate-conic, cylindroid, or mammillate, 2-10 mm; areoles circular, oval, pyriform, or elliptic, spiny and short or long woolly or glabrate; areolar glands absent; cortex and pith usually mucilaginous. Spines 3-45, reddish tan, pink, gray, or white, needle-shaped or awl-shaped to hairlike, 6-30 × 0.3-1 mm, smooth and hard, less often corky or spongy and soft, finely puberulent to glabrous; radial spines 3-35 per areole, spreading, erect, recurved, or somewhat pectinate, straight or irregularly curved, 1-32 mm; central spines 0-12, straight or curved upward, needlelike, hairlike, or corky, terete to flat. Flowers diurnal, borne at adaxial margins of areoles at stem apex, funnelform, 1-4 × 1-2.5 cm; outer tepals greenish or purple midstripes, pink or yellow margins, 9-25 × 3-9 mm, margins fringed, denticulate, or entire; inner tepals yellow, peach, pink, magenta, cream, or white, 4-15 × 3-7 mm, margins entire to fimbriate; ovary smooth, scaleless to few scaled, spineless; stigma lobes 5-9, yellow to green, 0.7-1.5 mm. Fruits dehiscent along 1 vertical suture, green or greenish yellow, often turning reddish brown, thin walled, cylindric, spheric or turbinate, 4-15 × 3-11 mm, becoming dry at maturity, smooth, scaleless or with few broad, thin scales; pulp greenish to white, scant; floral remnant deciduous. Seeds brown, black or gray, irregularly or obliquely obovoid or pyriform, 1.5-5 × 1-3.5 × 1-1.5 mm, papillate, sometimes also rugose, shiny; testa cells convex. x = 11.
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