6. Opuntia pottsii Salm-Dyck, Cact. Hort. Dyck. 1849: 236. 1850.
Opuntia ballii Rose; O. delicata Rose; O. filipendula Engelmann; O. macrorhiza Engelmann var. pottsii (Salm-Dyck) L. D. Benson
Shrubs, forming clumps, to 0.4 m, often from tuberlike rootstocks. Stem segments not easily detached, dark green, cuneate-obovate to commonly rhombic, 5-20 × 4-8 cm, fleshy but firm; areoles 4-6(-8) per diagonal row across midstem segment, oval to subcircular, 2-4 mm diam.; wool tan. Spines (0-)1-6 per areole, usually in distal 40% of stem segment, gray-white to red-brown, erect or reflexed, terete or proximal ones flattened, sometimes spirally twisted, longest to 60 mm, very slender, 0.2 mm diam. Glochids well developed in adaxial tuft , yellow or tan to brown-red, aging dull brown, to 6 mm. Flowers: inner tepals red throughout or with red basal portions, 25-35 mm; filaments pale yellow; anthers yellow; style whitish; stigma lobes cream to yellow. Fruits green to yellowish to dull red, long stipitate, elongate-obovoid, 25-40 × 15-40 mm, fleshy, base not narrowed, glabrous, spineless or nearly so; umbilicus deep; areoles 14-26. Seeds tan to gray, subcircular, 4-5 mm, thickish, warped; girdle protruding to 0.5 mm. 2n = 44.
Flowering late spring-early summer (May-Jul). Plains, hills, sandy or loamy soils; 900-1900 m; Ariz., N.Mex., Tex.; Mexico (Chihuahua).
Plants of Opuntia pottsii that are intermediate morphologically to O. macrorhiza are known in Arizona.