13. Opuntia chisosensis (M. S. Anthony) D. J. Ferguson, Cact. Succ. J. (Los Angeles). 58: 124. 1986.
Opuntia lindheimeri Engelmann var. chisosensis M. S. Anthony, Amer. Midl. Naturalist 55: 252, fig. 26. 1956
Shrubs, erect, to 1 m. Stem segments not easily detached, bluish to gray-green, flattened, circular to broadly obovate, 15-30 × 12-25 cm, nearly smooth, glabrous; areoles 5-7 per diagonal row across midstem segment, elliptic to obovate, 3-8 × 2-6 mm; wool tan, aging blackish. Spines 1-5 per areole, spreading, yellow to orange, tipped yellow, darkening with age (at higher elevations), or dark red-brown (lower elevations), ± acicular, longest 20-67 mm, terete to flattened near base, often curved. Glochids widely spaced, in crescent at adaxial margin of areole, partially encircling areoles, and in poorly developed subapical tuft, yellow, of irregular lengths, tending to elongate towards bases of areoles, to 4 mm. Flowers: inner tepals pale yellow to buff throughout, to 25-30 mm; filaments pale green; anthers and style yellow; stigma lobes green. Fruits reddish purple, ellipsoid to spheric, barrel-shaped, 33-45 × 40-50 mm, juicy, base not or little tapered, glaucous, spineless; areoles 16-20, mostly near apex. Seeds yellow to tan, 3.5-4.5 × 3-4 mm diam.; girdle protruding to 1 mm. 2n = 22.
Flowering late spring (May). Pine-oak and mixed conifer forests, grasslands; 1600-2200 m; Tex.
Opuntia chisosensis is local in the Chisos Mountains in western Texas, and it has been reported from Sierra del Carmen in Coahuila, Mexico by Ferguson, but this has not been confirmed by the author. It is perhaps related to, or part of, the O. azurea Rose complex in northern Chihuahuan Desert of Mexico.