Shrubs, prostrate (to erect), clambering, to 0.6 m. Stem segments easily detached, green, flattened, elliptic, 5-18 × 3-7 cm, slightly tuberculate, glabrous; areoles 3-4 per diagonal row across midstem segment, subcircular, 4 mm diam.; wool whitish. Spines 1-3(-4) per areole, ± evenly distributed on stem segment, porrect to spreading, gray to whitish or cream, tipped black, straight, acicular, to 40 mm, barbed. Glochids yellow, aging brown, 4-9 mm. Flowers: inner tepals yellow throughout, 20-25 mm; filaments pale green to yellow; anthers yellow; style pale green or white, pink tinged; stigma lobes color unknown. Fruits red, ovoid to obovoid, 25-30 × 15-20 mm, fleshy, glabrous, bearing few areoles, spineless. Seeds tan, subcircular, somewhat flattened, 2.5 mm diam.; girdle protruding less than 1 mm. 2n = 22.

Flowering year-round. Sandy areas on old limestone reefs, openings in tropical forests; 0 m; Fla.; West Indies.

Opuntia triacantha occurs in the flora area only on Big Pine Key, Florida. It is in the Center for Plant Conservation´s National Collection of Endangered Plants.