Kneiffia linifolia (Nuttall) Spach; Oenothera linifolia var. glandulosa Munz; Peniophyllum linifolium (Nuttall) Pennell

Herbs annual, caulescent, strig­illose or glabrous, also often glandular puberulent, especially distally; from a sparsely branched taproot. Stems un­branched or with many ascending branches arising near base, erect, 10–50 cm. Leaves in a basal rosette and cauline, basal 1–2(–4) × 0.2–0.6 cm, petiole 0.2–1(–1.5) cm, blade ovate to obovate or narrowly elliptic; cauline 1–4 × less than 0.1 cm, sessile, blade linear or filiform. Flowers usually 1–3 opening per day near sunrise; buds without free tips; sepals 1.5–2 mm; petals bright yellow, fading pink, obcordate to obovate, 3–5(–7) mm; filaments 1–2 mm, anthers 0.5–1 mm; style 1–2 mm, stigma surrounded by anthers at anthesis. Capsules ellipsoid-rhombic to subglobose, 4-angled, 4–6(–10) × 1.5–3 mm, stipe 0–4 mm, valve midrib raised at distal end, indehiscent or tardily dehiscent distally; sessile. Seeds clustered in each locule, ovoid, surface minutely papillose, 1 × 0.5 mm. 2n = 14.

Flowering Apr–Jun(–Aug). Prairies, open woodlands, open rocky and sandy sites, roadsides; 0–400 m; Ala., Ark., Fla., Ga., Ill., Kans., Ky., La., Miss., Mo., N.C., Okla., S.C., Tenn., Tex.

Kneiffia linearifolia Spach (1835) is an illegitimate name based on Oenothera linifolia.