Flora of North America species comparison

pale gray-green (desert populations) to grass green (eastern populations), above-ground portion flat-topped, hemispheric in old age but usually deep-seated, flush with soil surface, 10–30 × 10–30 cm;

ribs 13–27, very prominent, straight, vertical, or sinuous on desiccated plants, crests ± sharp, without depressions between areoles but sometimes areoles recessed part way into rib.

(6–)7–8 per areole, mostly decurved or 1 porrect and straight, pale tan, pink, reddish to gray, terete to flattened, annulate, not hiding stem surfaces, minutely canescent with laterally compressed unicellular trichomes;

radial spines (5–)6–7 per areole;

central spine 1 per areole, porrect or descending, straight or distally decurved, (20–)40–60(–80) × 1.5–4(–8) mm.

5–6 × 5–6 cm;

inner tepals bright rose-pink to pale silvery-pink, proximally orange to red, (15–)28–32 × (3–)6(–9) mm, margins usually erose;

stigma lobes pink to pinkish white.

indehiscent (rarely rupturing irregularly), scarlet or crimson, spheric to ovoid, 15–50 × 15–40 mm, fleshy, surfaces not hidden by widely spaced hairs in axils of scales;

scales 13–21, distal scales spine-tipped, minutely puberulent.

black, spheric-reniform or irregularly obovoid, 2.5–3 mm, glossy;

testa cells flat or very slightly convex.

= 22.