Oenothera laciniata Hill var. grandiflora (S. Watson) B. L. Robinson; O. sinuata Linnaeus var. grandiflora S. Watson; Raimannia grandis (Smyth) Rose ex Sprague &L. Riley

Herbs annual, strigillose and sparsely villous, also glandular puberulent distally. Stems erect to ascending, often with ascending lateral branches, 15–60(–100) cm. Leaves in a basal rosette and cauline, basal 5–13 × 1–3 cm, cauline 3–10 × 1.5–3.5 cm; blade green, narrowly oblanceolate to narrowly elliptic, margins lobed or dentate, lobes often dentate; bracts spreading, flat. Flowers 1–few opening per day near sunset; buds erect, with free tips terminal, erect or hornlike, 1.5–5 mm; floral tube 25–45 mm; sepals 15–30 mm; petals yellow, very broadly obovate or shallowly obcordate, 25–40 mm; filaments 12–22 mm, anthers 4–11 mm, pollen 85–100% fertile; style 40–75 mm, stigma exserted beyond anthers at anthesis. Capsules cylindrical, sometimes slightly enlarged toward apex, 25–50 ×2–3 mm. Seeds broadly ellipsoid to subglobose, 0.8–1.5 × 0.5–0.9 mm. 2n = 14.

Flowering Mar–Sep. Open, sandy sites; 0–1500(–2200) m; Ala., Ark., Colo., Conn., Fla., Ill., Ind., Kans., La., Md., Mich., Mo., Nebr., N.J., N.Mex., N.C., Tex.; Mexico (Tamaulipas).

Oenothera grandis is probably native to eastern New Mexico and Colorado, Arkansas, Kansas, Louisiana, Missouri, Nebraska, Oklahoma, and Texas, and northeastern Tamaulipas, Mexico. Scattered collections made in other states probably represent introductions (W. Dietrich and W. L. Wagner 1988).

Oenothera grandis is self-incompatible (W. Dietrich and W. L. Wagner 1988).

Oenothera laciniata Hill var. occidentalis Small and O. laciniata var. grandis Britton are illegitimate superfluous names based on O. sinuata Linnaeus var. grandiflora S. Watson and pertain here.