Plants stem succulents, unbranched [to several branched from base], mostly low and deep-seated in substrate [taller in Mexican species]. Roots diffuse. Stem unsegmented, dark green or gray-green, hemispheric or depressed-spheric [to spheric or short cylindric], (2.5-)6-15(-60)[-100] × 6-10(-20) cm, speckled [or entirely hidden] by numerous tufts of dense, whitish, multicellular hairs less than 0.5 mm; ribs [4-]8-10, crests uninterrupted, straight [to sinuous and/or helically curving around stem], broad and nearly flat or rounded [sharp or keeled]; areoles distinct, [2-]6-9[-20] mm apart along ribs, circular; areolar glands absent; cortex and pith hard, not mucilaginous. Spines absent [1-25 per areole in some Mexican species]. Flowers diurnal, near stem apex, at adaxial edge of areoles, funnelform, 4.5-5.4[-8] × 3.8-5.2[-6] cm; inner tepals yellow, proximally red [all yellow], 25 × 6-10[-12] mm, margins entire; ovary sparsely to densely scaly, axils spineless long hairy with arachnoid trichomes, distal scales spine-tipped; stigma lobes [8-]10-12, yellow [pale yellowish], 4 mm. Fruits indehiscent or splitting irregularly, green or pinkish to red, ovoid to spheric, 15-20 × 12 mm, initially fleshy, drying immediately after ripening, sparsely to densely scaly with spine-tipped scales; axils of scales long woolly, spineless; floral remnant persistent. Seeds dark brown to blackish, appearing hollow or bowl-shaped from strongly expanded, inrolled rim around sunken hilum, 2-3 mm in greatest dimension, nearly smooth; testa cells very slightly convex. x = 11.
|[Greek asteros, star, in reference to the star-shaped stem cross section of the type species, and phyton, plant]|