Proc. Amer. Acad. Arts 3: 298. 1856.
Shrubs, forming clumps, 1–2 (–3) segments tall, to 7–40 cm. Stem segments not disarticulating, blue to yellow-green, sometimes tinged maroon-purple, flattened, spatulate to broadly obovate or subcircular, thick, 5–22 (–35) × 2–13.5 (–16) cm, nearly smooth, papillose to puberulent (rarely glabrous); areoles 4–16 (–19) per diagonal row across midstem segment, circular to elliptic, 3–5 × 3 mm; wool white to tan, aging gray. Spines 0 (–8) per areole, when present, usually in distal areoles, spreading, yellow, straight, acicular, 5–25 mm. Glochids numerous, nearly filling areoles, yellow to redbrown or dark-brown, to 3 mm. Flowers: inner tepals pink to magenta throughout (rarely white), 25–40 mm; filaments red-magenta (rarely pale); anthers yellowish; style white to pink; stigma lobes white to cream. Fruits maturing tan, 20–40 × 15–23 mm, dry at maturity, puberulent, spineless (except in var. treleasei); umbilicus 5–12 mm deep; areoles 24–76. Seeds yellowish to tan, ± subspheric but angular, thick, 6.5–9 × 6.5–7 mm, sides smooth or bearing 1–3 depressions; girdle protruding to 1 mm.
Ariz., Calif., Nev., Utah, n Mexico
Varieties 4 (4 in the flora).
|1||Stem segments bearing spines in at least several of distal areoles||Opuntia basilaris var. treleasei|
|1||Stem segments essentially spineless (rarely 1-few per stem segment)||> 2|
|2||Stem segments broadly obovoid to subcircular, erect; areoles (8-)10-16(-19) per diagonal row across midstem segment||Opuntia basilaris var. basilaris|
|2||Stem segments spatulate to elongate, oblong, usually decumbent; areoles 4-8(-9) per diagonal row across midstem segment||> 3|
|3||Stem segments spatulate, apex rounded; areoles 4-8(-9) per diagonal row across midstem segment; Arizona, Utah.||Opuntia basilaris var. longiareolata|
|3||Stem segments oblong to narrowly spatulate to subcylindric, apex truncate to rounded; areoles 4-6(-7) per diagonal row across midstem segment; California||Opuntia basilaris var. brachyclad|