3. Grusonia emoryi (Engelmann) Pinkava, J. Arizona-Nevada Acad. Sci. 32: 50. 1999.
Opuntia emoryi Engelmann, Proc. Amer. Acad. Arts 3: 303. 1856; Corynopuntia stanlyi (Engelmann ex B. D. Jackson) F. M. Knuth; Grusonia stanlyi (Engelmann ex B. D. Jackson) H. Robinson; O. stanlyi Engelmann ex B. D. Jackson
Shrubs, forming mats, 15-30 cm. Roots diffuse. Stem segments curved-clavate, gradually to abruptly narrowed at base, 7-19 × 2.5-5 cm; tubercles very prominent, 20-50 mm, 1-3.5 times longer than wide, not or little obscured by spines; areoles 4-6 mm in diam.; wool white to gray. Spines 12-30 per areole, mostly in apical areoles to ± uniformly distributed along stems (in northern populations), spreading, yellow, tan, or red-brown, tipped yellow, longest 3-7 cm; major 3-5 abaxial spines divergent, yellowish or red-brown, angular-flattened, sharp-edged; major (1-)3-5 adaxial spines ascending-divergent, tan or red-brown, angular-flattened to subterete. Glochids adaxial in areole, yellow to brown, 5-7 mm. Flowers: inner tepals yellow, 20-30 mm; filaments yellow to reddish; style cream; stigma lobes cream or tinged pink. Fruits yellow, cylindric to ellipsoid, 40-90 × 14-40 mm, fleshy, spineless (rarely with few very short spines) but usually densely yellow glochidiate; areoles 30-45. Seeds yellowish white to yellow, 5-6 × 3.5-4 mm, smooth. 2n = 44.
Flowering late spring (May-Jun). Chihuahuan and Sonoran deserts, sandy or gravelly desert flats, washes, hills; 700-1200 m; Ariz., N.Mex., Tex.; Mexico (Chihuahua).