Thistle Cholla

Shrubs, densely branched, 0.2-0.6 m; roots with elongate, tuberlike swellings. Stem segments easily detached, whorled, obscuring trunks, light green, 4-6 × 0.8-1.2 cm; tubercles prominent, 1-2 cm; areoles subcircular, 2-3.5 mm in diam.; wool tan. Spines 7-13(-21) per areole, at most areoles, spreading, obscuring stems, yellow- to red-brown to nearly black, tipped yellow, subterete to angularly flattened, the longest 1.5-5 cm; sheaths loose fitting, ± yellow to tan, 1.5-2 mm diam. Glochids in adaxial tuft, yellow, 2-4 mm. Flowers: inner tepals yellow-green, tinged purple-red, aging reddish brown or bronze, spatulate, 15 mm, apiculate; filaments pale green basally to purplish distally; anthers orange-yellow; style cream to pale green, sometimes faint purple-pink distally; stigma lobes very pale green. Fruits usually sterile, often in chains of 2, yellow, top-shaped, 20-30 × 10-20 mm, pulpy, tuberculate, spineless (rarely few-spined); tubercles subequal; umbilicus 5-8 mm deep; areoles 20-35. Seeds, when present, yellow-tan, subcircular, flattened, 3 mm diam., sides smooth; girdle narrow, not protruding. 2n = 22, 44 (one count).

N.Mex., Okla., Tex.

Flowering late spring (May-Jun).

Grasslands, oak-juniper-mesquite woodlands, plains or slopes, sandy to loamy soils; 600-1500m.

Opuntia davisii Engelmann & J. M. Bigelow, Proc. Amer. Acad. Arts 3: 305. 1856; O. tunicata (Lehmann) Link & Otto var. davisii (Engelmann & J. M. Bigelow) L. D. Benson