Herbs winter or spring annual, acaulescent or short-caulescent, glandular puberulent, some­times also sparsely hirsute; from a taproot. Stems (when present) 1–several, ascending, usually unbranched, 2–4 cm. Leaves primarily in a basal rosette, sometimes also cauline, (0.5–)2.5–13(–19.5) × (0.2–)0.6–2.3(–2.7) cm; petiole 0.5–5.2 cm; blade oblanceolate to elliptic-oblanceo­late (in some exceptionally large leaves), margins lyrate-pinnatifid to subentire (in very small ones), apex usually rounded, rarely acute. Flowers 1–3(–10) per stem opening per day near sunset, without noticeable scent; buds sometimes ± recurved before anthesis; floral tube (20–)30–37(–47) mm; sepals 4.5–12 mm; petals white, fading pale pink, (6.5–)8–20(–25) mm; filaments 5.2–7.5(–12) mm, anthers (1.4–)3–4.5(–6) mm; style (24–)35–45(–56) mm, stigma surrounded by anthers at anthesis. Capsules falcate (especially before maturity), ellipsoid-ovoid to ovoid, obtusely 4-angled, 12–38 × 6–14 mm, tapering to a sterile beak 2–8 mm, dehis­cent to 1/2 their length, valve margins with a sinuate ridge or 8–20 nearly distinct tubercles; pedicel 0–10 mm. Seeds usually numerous, sometimes as few as 5, in 2 adjacent rows per locule, obovoid, 2.5–3.1 × 1.1–1.4 mm, embryo 1/2 of seed volume, surface minutely papillose to reticu­late; seed collar without membrane, producing a large empty cavity, margin irregularly sinuate. 2n = 14.

Flowering Mar–May. Exposed calcareous slopes, crevices in limestone, dolomite, or loose talus, sandy arroyos, sandstone, granitic crevices, volcanic cinders in Mojave Desert or Great Basin scrub communities, rarely in arid juniper woodlands; of conservation concern; 400–1700 m; Ariz., Calif., Nev.

Oenothera cavernae is known from the Arrow Canyon, Las Vegas, and Sheep ranges and the low hills near Arden and Sloan in Clark County, Nevada, eastward along the Grand Canyon to the vicinity of Page, Arizona, and perhaps Washington County, Utah and formerly in Glenn Canyon, and more recently collected in eastern San Bernardino County, Cali­fornia (eastern Clark Mountain Range, and the base of range in Ivanpah Valley). W. L. Wagner et al. (1985) deter­mined O. cavernae to be self-compatible and autogamous.