Opuntia engelmannii var. engelmannii
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.
Phenology: Flowering spring (Apr–Jul).
Habitat: Deserts, grasslands, woodlands, plains, sandy soils to rocky hillsides, lower to midslopes of mountains
Elevation: 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.