27. Hamatocactus Britton & Rose, Cact. 3: 104, figs. 110-114. 1922.
Twisted-rib cactus [Latin hamatus, hooked, in reference to the hooked central spines, and Cactus, an old genus name]
Allan D. Zimmerman & Bruce D. Parfitt
Plants erect, unbranched or branched in basal portion, not deep-seated in substrate. Roots diffuse. Stems unsegmented, bright deep green, hemispheric when young, becoming spheric or ovoid to cylindric, 3.6-12(-20) × 4.5-12 cm, glabrous; ribs 13, spiraling or vertical, slender, crests sinuate, sharp, not interrupted or undulate, narrow; areoles circular or, on older parts of stem, elliptic to ovate, adaxially elongated into short areolar grooves; areolar glands golden, darker with age, cylindric or peglike; cortex and pith firm, not mucilaginous. Spines 11-20 per areole, not obscuring stems, yellowish, whitish, or reddish brown, acicular (rarely central spine flattened), longest spines 12-38 mm; radial spines 10-19 per areole, straight or slightly curved toward stem, longest spines 11-32 mm; central spines 1 per areole, porrect, hooked, terete (rarely flattened). Flowers diurnal, near stem apex, at adaxial edge of areoles or at axillary ends of short areolar grooves, widely funnelform, 3.7-7 × 4-7 cm; outer tepals finely fringed; inner tepals yellow (to ivory) with red bases, 20-25 × 6-9 mm, margins entire, toothed, or lacerate; ovary scaly, hairless, spineless; stigma lobes 5-11, pale yellow to orangish, 3-7 mm. Fruits indehiscent or eventually dehiscent by vertical slits, bright red, spheric or nearly so, ca. 10 × 8-13 mm, fleshy, with 15 or fewer whitish, broad fringed, naked, spineless scales; floral remnant persistent. Seeds black, obovoid, usually 1-1.4 × 0.8-1 mm, minutely papillate; testa cells weakly convex, nearly flat toward proximal end of seed. x = 11.
Species 1: arid regions, sw United States, Mexico.
Hamatocactus has been submerged in Ferocactus or Thelocactus by various authors and grouped with Glandulicactus by others.