Herbs biennial, densely to sometimes sparsely strigillose, or also sparsely glandular puber­ulent distally. Stems sometimes with lateral branches arising obliquely from rosette, 20–70(–100) cm. Leaves in a basal rosette and cauline, basal 5–16 × 0.5–1.5 cm, cauline 2–12 × 0.5–2 cm; blade narrowly oblanceolate, gradually narrowly elliptic to narrowly lanceolate distally, margins lobed to remotely dentate or subentire; bracts slightly longer than capsule they subtend. Inflorescences dense, without lateral branches, mature buds usually not overtopping spike apex. Flowers 2–several per spike opening per day near sunset; buds erect, with free tips erect, 0.5–2 mm; floral tube slightly curved upward to ± straight, 15–40 mm; sepals 6–13 mm; petals yellow, broadly elliptic to rhombic-ovate, 5–16 mm; filaments 4–18 mm, anthers 2–3.5 mm, pollen ca. 50% fertile; style 20–40 mm, stigma surrounded by anthers at anthesis. Capsules narrowly lanceoloid, 10–20 ×2–3 mm. Seeds brown, sometimes flecked with dark red spots, ellipsoid, 1–1.9 × 0.4–0.8 mm. 2n = 14.

Flowering Jun–Aug(–Sep). Fields, prairies, sandy soil; 150–300 m; Ont.; Ark., Ill., Ind., Iowa, Ky., Mich., Minn., Mo., N.J., N.Y., Va., Wis.

Oenothera clelandii is a PTH species and forms a ring of 14 chromosomes in meiosis, and is self-compatible and autogamous (W. Dietrich and W. L. Wagner 1988). Some localities in the easternmost states may represent introductions, primarily occurring in disturbed areas along roads and railroad lines.