Cact. 3: 104, figs. 110–114. 1922.
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.
Arid regions, sw United States, Mexico.
Hamatocactus has been submerged in Ferocactus or Thelocactus by various authors and grouped with Glandulicactus by others.