Phytologia 26: 176. 1973.
Shrubs, forming mats, 7.5–9 cm. Roots diffuse. Stem segments clavate, (2–) 3.5–6.5 × (1.5–) 2–3 cm; tubercles 8–20 mm, 1–3.5 times longer than wide, not or little obscured by spines; areoles 2.5–4 mm in diam.; wool white to yellowish. Spines 11–17 per areole, mostly in distal areoles, spreading to deflexed, white, tan, or redbrown, longest 3–7 cm; major 3 abaxial spines divergent or deflexed, tan to brown, flattened to angular-flattened, sharp-edged; major 2–3 adaxial spines ascending-divergent, redbrown, subterete to angular-flattened. Glochids adaxial in areole, yellowish white to yellow, to 7 mm. Flowers: inner tepals bright-yellow, ± 20 mm; filaments yellow; style cream; stigma lobes cream or tinged pink. Fruits yellow, cylindric to ellipsoid, 30–50 × 10–30 mm, fleshy, spineless (sometimes with 3–6 white or red spines to 6 mm), yellow glochidiate; areoles 25–35. Seeds yellowish white to yellow, 4.5–5 × 3.5 mm, smooth. 2n = 44.
Phenology: Flowering late spring–early summer (Jun–Jul).
Habitat: Chihuahuan Desert, sandy or gravelly flats, low hills
Elevation: 700-1200 m
Tex., Mexico (Coahuila)
Plants restricted to clay soils in Big Bend National Park, Brewster County, Texas, with more spines per areole than Grusonia schottii, have been named G. densispina (Ralston & Hilsenbeck) Pinkava. Much additional study is required to determine the relationship between such plants and G. schottii.