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 redbrown 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.