Opuntia kelvinensis V. E. Grant & K. A. Grant, Evolution 25: 155, fig. 5. 1971

Trees 1.5-2 m; trunk commonly branched; crown open to compact usually bearing whorled branches. Stem segments often easily dislodged, if terminal, green or purple, 5-13 × 1.8-3 cm; tubercles prominent, broadly oval, 0.7-1.2(-1.5) cm; areoles obdeltate to rhombic, 4.5-6 × 3-5 mm; wool yellow, aging gray to black. Spines 0-8(-13) per areole, sometimes with 1-3 bristlelike spines along areole margins at most areoles, usually slightly interlacing with spines of adjacent areoles, yellowish to tan, sometimes with pinkish hue, to red-brown and partially gray coated, aging brown-gray to gray; major abaxial spines angular-flattened, usually reflexed, the longest to 30 mm; major adaxial spines subterete, erect-divergent, the longest to 18 mm; sheaths uniformly whitish or tipped yellow to gold, slightly baggy. Glochids in inconspicuous adaxial crescent, yellow, to 1 mm. Flowers: inner tepals rose to magenta, spatulate, 18-25(-30) mm, emarginate-apiculate; filaments deep rose; anthers yellow; style white, tinged red-purple distally; stigma lobes white with hint of green. Fruits usually sterile, sometimes forming short chains, yellow-green to yellow, sometimes purplish, 25-45 × 15-22 mm, fleshy, tuberculate, spineless; tubercles progressively longer toward fruit apex; umbilicus 4-7 mm deep; areoles 32-44. Seeds pale yellow, orbicular to angular or squarish in outline, flattened to warped, 3.5-4 × 3-4 mm, sides with 0-2 large depressions; hilum sometimes pointed; girdle smooth. 2n = 22, 33.

Flowering spring (Apr-Jun). Sonoran desert scrub, edges of grasslands, rocky flats and slopes, rolling hills; 500-1000 m; Ariz.