Stem segments erect, flattened, obovate, 9-20 × 5-7.5 cm; areoles 7-8 per diagonal row across midstem segment, circular. Spines 2-8 per areole, usually in distal areoles, spreading, yellow, straight, acicular, terete, 5-25 mm. Fruits with few, pale yellow spines. 2n = 33.

Flowering spring (Mar-Apr). Grasslands; of con-servation concern; 100-200 m; Calif.

Opuntia basilaris var. treleasei is in the Center for Plant Conservation´s National Collection of Endangered Plants.