Stem segments broadly obovate to circular, (4-)8.5-12 × (4-)5.5-11 cm; areoles 6-11 per diagonal row across midstem segment, 6-13 mm apart. Spines in most areoles, of 2 kinds: major spines (0-)1-3(-5) per areole, ± deflexed to reflexed or porrect at stem segment apex, yellow-brown to gray, 20-35(-40) mm; minor spines 0-5 per areole, deflexed, white, 5-10(-16) mm, sometimes spines of basal and near basal areoles are long, flexible, curling. Fruits stout; areoles 12-28, most bearing (4-)6-15 spines, 5-10 mm. 2n = 22, 44. Flowering late spring. Grasslands, pinyon-juniper woodlands, clay, sandy or gravelly soils; 500-2000(-2800) m; Alta., Sask.; Ariz., Colo., Idaho, Kans., Mont., Nebr., Nev., N.Mex., N.Dak., Okla., S.Dak., Tex., Utah, Wyo. The morphotype, usually called Opuntia trichophora, has additional, curly, hairlike spines from areoles on older stem segments, but these plants occur sporadically throughout the range of O. polyacantha var. polyacantha from New Mexico to Wyoming.
PADS: broadly obovate to circular, (4-)8.5-12 cm long, (4-)5.5-11 cm broad. AREOLES: 6-13 mm apart, 6-11 in a row diagonal across midpad. SPINES: in most areoles, of two kinds: major spines yellow-brown to gray, deflexed to reflexed or porrect at pad apex, 1-3(-5) per areole, 2-3.5(-4) cm long; minor spines white, deflexed, 0-5, per areole, 5-10(-16) mm long. FRUITS: stout; areoles 12-28 most bearing (4-)6-15 spines, 5-10 mm long. 2n = 22, 44. NOTES: See also parent taxon. Clay, sandy or gravelly soils, grasslands to pinyon-juniper woodlands, Apache, Navajo Cos.; 500-2000(-2750) m (1600-6500 [-9100] ft);late spring; Alta., Sask. to ND s to AZ, Chih. and TX. REFERENCES: Pinkava, Donald J. Cactaceae. 2003. J. Ariz. - Nev. Acad. Sci. Volume 35(2).