Suppl. Pl. Succ., 82. 1819.
Shrubs, low, forming mats, 2–10 cm. Stem segments easily detached when terminal, dark green, subspheric to subcylindric, to flattened and elliptic obovate, (1.5–) 2–5.5 × (1–) 1.5–3 cm, low tuberculate (pronounced when dried), glabrous; areoles 3–5 per diagonal row across midstem segment, oval, 3 × 2.5 mm; wool white. Spines 3–8 per areole, in most areoles spreading, gray with brown tips, straight, ± acicular, terete, the longest 8–24 mm; depressed spines at base of areoles 0–3, 1–3 mm. Glochids in crescent at adaxial margin of areole, tan to brown, inconspicuous, to 3 mm. Flowers: inner tepals yellow, sometimes basally red, 20–26 mm; filaments white or red; anthers yellow; style white; stigma lobes green. Fruits tan, 10–30 × 8–15 mm, dry, glabrous; areoles 12–22, distal areoles bearing 1–6 short spines. Seeds tan to gray, flattened, warped, oblong to subcircular, 5–6 mm diam.; girdle protruding 1–1.5 mm. 2n = 66.
Phenology: Flowering summer (late Jun-early Jul).
Habitat: Barren areas in grasslands, woodlands, sandy or gravelly soils, on outcrops of granite, limestone, or quartzite
Elevation: 0-2400 m
Alta., B.C., Man., Ont., Sask., Ariz., Calif., Colo., Idaho, Ill., Iowa, Kans., Mich., Minn., Mont., Nebr., N.Mex., N.Dak., Okla., Oreg., S.Dak., Tex., Utah, Wash., Wis., Wyo.
Opuntia fragilis is a widespread, though inconspicuous, species; in many places, it flowers infrequently, if at all. Its easily detached stem segments are dispersed by animals and possibly water.