Cac t. Succ. J. (Los Angeles) 50: 294. 1978.
Plants usually unbranched, spine-bearing areoles with long white wool obscuring basal portion of spine. Roots diffuse or short taproots. Stems deep-seated (buried except for its apical 0.5–3 cm), 2–10 × 2–6 cm; tubercles 5–8 × 4–6 mm, moderately soft; areolar glands absent. Spines 11–20 per areole, white, largest spines dark tipped when fresh, straight; radial spines 10–20 per areole, 8–18 × 0.2–0.5 mm; central spines 0 (–1) per areole, similar to largest radial spines, but porrect, ca. 8–18 mm. Flowers nearly apical, 12–29 × 10–18.5 mm; outer tepals fringed; inner tepals 14 per flower, dull yellow, frequently tinted greenish or bronze, often with midstripes of brownish or dull pink; outer filaments greenish; anthers bright-yellow; stigma lobes green or yellow-green. Fruits bright-orange-red or scarlet, spheric to obovoid, 6–8.5 × 3–4.5 mm, slightly juicy, quickly drying and turning brownish; floral remnant weakly persistent, often deciduous through breakage not abscission. Seeds dark-brown, drying blackish, spheric, 1.3–1.4 mm, pitted. 2n = 22.
Phenology: Flowering Mar–Apr; fruiting Jun–Aug.
Habitat: Semidesert grasslands, limestone hills
Elevation: 1300-1500 m
Ariz., Mexico (Sonora)
Of conservation concern.
Coryphantha robbinsorum is somewhat intermediate between the C. dasyacantha species-group, especially C. zilziana Boedeker, and the C. missouriensis species-group.
Coryphantha robbinsorum is in the Center for Plant Conservation’s National Collection of Endangered Plants.