24. Opuntia microdasys (Lehmann) Pfeiffer, Enum. Diagn. Cact. 154. 1837.
Cactus microdasys Lehmann, Index Seminum (Hamburg), 1827: 16. 1827
Shrubs, erect to sprawling, to 1 m, with many small stem segments. Stem segments not disarticulating, bright green, flattened, circular to elliptic-obovate, (5-)7-10(-15) × (3-)4-8(-10) cm, low tuberculate, puberulent; areoles (9-)11-16 per diagonal row across midstem segment, subcircular, 2-5 mm diam.; wool white to tan, aging gray. Spines absent. Glochids numerous, nearly filling areole, usually yellow or whitish, sometimes reddish brown, to 3 mm. Flowers: inner tepals bright yellow throughout, aging peach, 25-30 mm; filaments and style white; anthers yellowish; stigma lobes dark green. Fruits red, spheric to ovoid, 20-25 × 12-16 mm, fleshy, pubescent, spineless; areoles 35-50. Seeds tan, nearly spheric (slightly flattened), 1-1.2 mm (perhaps infertile); girdle protruding to 0.5 mm. 2n = 22.
Flowering spring (Apr-May). Desert hills, uplands, sandy to loamy calcareous soils; 1700-2100 m; introduced; Ariz.; Mexico (Coahuila, Durango, Nuevo León, San Luis Potosí, Zacatecas).
Opuntia microdasys is widely cultivated and sometimes naturalized in Arizona. In Mexico, O. microdasys hybridizes with O. rufida.