Oenothera biennis Linnaeus var. grandiflora (L’Héritier) Lindley; O. grandiflora var. glabra Seringe; O. grandiflora var. pubescens Seringe; O. lamarckiana Seringe; O. spectabilis Lehmann

Herbs biennial, often appearing glabrous to naked eye, usually sparsely to moderately strigillose and villous with pustulate, translucent hairs proximal to inflorescence, pustules not red (in fresh material), inflorescence glabrous, glandular puberulent, or strigillose and glandular puberulent. Stems erect, red on proximal parts, usually green on distal ones, rarely red throughout, unbranched or with branches obliquely arising from rosette and secondary branches arising from main stem, 100–300(–400) cm. Leaves in a basal rosette and cauline, basal 18–32 × (2–)3–6.5 cm, cauline 6–20 × 1.5–6.5 cm; blade soft and thin, bright green, usually flat, rarely undulate, narrowly oblanceolate to narrowly obovate, or narrowly elliptic to elliptic, sometimes narrowly ovate distally, margins bluntly dentate or subentire, teeth widely spaced, sometimes sinuate-dentate proximally or lobed; bracts usually caducous. Inflorescences erect, often with secondary or tertiary branches just proximal to main one. Flowers opening near sunset; buds erect, 5–9 mm diam., with free tips terminal, erect, 2–9 mm; floral tube 35–55 mm; sepals yellowish green or flushed with red, 22–46 mm; petals yellow to pale yellow, fading pale yellowish white, very broadly obcordate or obovate, (25–)30–45 mm; filaments 18–27 mm, anthers 10–15 mm, pollen 90–100% fertile; style 57–90 mm, stigma exserted beyond anthers at anthesis. Capsules erect or slightly spreading, dull green when dry, narrowly lanceoloid to narrowly ovoid, 15–35 × 3.5–5.5 mm, free tips of valves 0.5–2.5 mm. Seeds 1–1.7 × 0.6–1.2 mm. 2n = 14.

Flowering Jul–Aug(–Sep). Scattered, presumably relictual populations on chalky bluffs, loose sand over limestone, along streams, marshes, ditches, roadsides; 20–600 m; Ala., Fla., Miss., N.C., S.C., Tenn.

Oenothera grandiflora has a scattered distribution, from the eastern half of Mississippi and Alabama, east to Tennessee (Franklin and Marion counties), North Carolina (Cherokee, Macon, Martin, Moore, New Hanover, Sampson, and Swain counties), South Carolina (Oconee, Spartanburg, and Sumter counties), and Florida (Alachua, Escambia, Franklin, Lake, Leon, Polk, Putnam, and Santa Rosa counties). Collections from southern Canada, New York, Pennsylvania, Vermont, and West Virginia almost certainly represent cultivated plants, garden escapes, or adventive populations, and the single locality from central Kentucky also may be an introduction; it is sometimes a colonizer in disturbed sites such as along roads.

Oenothera grandiflora has plastome III and a BB genome composition. As summarized by W. Dietrich et al. (1997), some populations of O. grandiflora seem to be entirely or mostly composed of self-incompatible individuals, whereas others consist of self-compatible plants. This is an extremely uncommon phenomenon within a single species of Oenothera; the only other species known to exhibit mixed populations of self-incompatible and self-compatible individuals is O. primiveris.

Oenothera grandiflora Lamarck 1798, being a later homonym of O. grandiflora L’Héritier 1789, pertains here.