Stem segments circular to obovate to rhombic, 20-40 × 17-30 cm, to 1.5 times longer than wide. Spines (0-)1-5(-12) per areole, absent or at most areoles, chalky white, yellow when wetted, aging gray to black, usually with red-brown extreme bases, longest 20-50(-75) mm. 2n = 66 . Flowering spring (Apr-Jul). Deserts, grasslands, woodlands, plains, sandy soils to rocky hillsides, lower to midslopes of mountains; 300-2700 m; Ariz., Calif., Nev., N.Mex., Tex., Utah; Mexico. In Arizona, California, and New Mexico, Opuntia engelmannii var. engelmannii hybridizes with O. phaeacantha yielding numerous named and unnamed hexaploid forms, including O. wootonii Griffiths; the various intermediates have 2n = 66. Hybrid swarms occur in both Zion and Grand Canyon national parks; these plants were perhaps brought in to the parks by native peoples as a food source and they are associated with agaves also believed to have been imported.

PADS: circular, rhombic to obovate, 20-40 cm long, 17-30 cm broad. SPINES: absent or at most areoles, chalky-white, yellow when wetted, aging gray to black, usually with ± red-dark brown extreme bases, (0-)1-5(-12) per areole, the largest 2-5(-7.5) cm long. Fruit usually edible. 2n = 66 (only once reported as 44 in TX). NOTES: See also parent taxon. Sandy soils to rocky hillsides, deserts, grasslands, woodlands, on plains and lower to mid-slopes of mountains; Cochise, Coconino, Gila, Graham, Maricopa, Mohave, Pima. Pinal, Santa Cruz, Yavapai cos.; 300-2650 m (1000-8700 ft); Apr-Jul; CA, NV, NM, TX, UT; adjacent Mexico. Var. engelmannii hybridizes with O. phaeacantha yielding numerous named and unnamed forms in AZ, CA and NM; the various intermediates counted are 2n = 66. REFERENCES: Pinkava, Donald J. Cactaceae. 2003. J. Ariz. – Nev. Acad. Sci. Volume 35(2).