Enum. Diagn. Cact., 154. 1837.
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.
Phenology: Flowering spring (Apr–May).
Habitat: Desert hills, uplands, sandy to loamy calcareous soils
Elevation: 1700-2100 m
Introduced; Ariz., Mexico (Coahuila), Mexico (Durango), Mexico (Nuevo León), Mexico (San Luis Potosí), Mexico (Zacatecas)
Opuntia microdasys is widely cultivated and sometimes naturalized in Arizona. In Mexico, O. microdasys hybridizes with O. rufida.