Opuntia polyacantha var. arenaria
Cact. Succ. J. (Los Angeles) 70: 188. 1998.
Stem segments narrowly obovate, 4–7 × 2–3 (–5) cm; areoles 4–6 per diagonal row across midstem segment, 8–11 mm apart. Spines in most areoles, of 2 kinds: major spines 1–3 per areole, only in distal 3–9 areoles, reflexed to porrect, brown, longest 20–40 mm; minor spines 5–7 per areole, strongly deflexed, white, 4–7 mm, except middle one to 14 mm. Fruits slender; areoles 10–14, bearing 3–6 spines, to 8 mm. 2n = 22.
Phenology: Flowering late spring.
Habitat: Sandy barren areas, small dunes
Elevation: 1000-1300 m
N.Mex., Tex., Mexico (Chihuahua)
Of conservation concern.
"longest" is not a number.