4. Grusonia schottii (Engelmann) H. Robinson, Phytologia. 26: 176. 1973.
Opuntia schottii Engelmann, Proc. Amer. Acad. Arts 3: 304. 1856; Corynopuntia schottii (Engelmann) F. M. Knuth
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 red-brown, 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, red-brown, 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.
Flowering late spring-early summer (Jun-Jul). Chihuahuan Desert, sandy or gravelly flats, low hills; 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.