Oenothera tetragona Roth, Catal. Bot. 2: 39. 1800; Kneiffia fraseri (Pursh) Spach; K. fruticosa (Linnaeus) Spach ex Raimann var. differta (Millspaugh) Millspaugh; K. glauca (Michaux) Spach; K. latifolia Rydberg; K. serotina (Lehmann) Bartling; K. tetragona (Roth) Pennell; K. tetragona var. hybrida (Michaux) Pennell; O. ambigua (Nuttall) Sprengel; O. canadensis Goldie; O. fraseri Pursh; O. fruticosa var. ambigua Nuttall; O. fruticosa var. differta Millspaugh; O. fruticosa var. fraseri (Pursh) Hooker; O. fruticosa subsp. glauca (Michaux) Straley; O. fruticosa var. glauca (Michaux) H. Léveillé; O. fruticosa var. incana (Nuttall) Hooker; O. fruticosa var. maculata H. Léveillé; O. glauca Michaux; O. glauca var. fraseri (Pursh) Torrey & A. Gray; O. hybrida Michaux; O. hybrida var. ambigua (Nuttall) S. F. Blake; O. incana Nuttall; O. serotina Lehmann; O. tetragona var. fraseri (Pursh) Munz; O. tetragona subsp. glauca (Michaux) Munz; O. tetragona var. hybrida (Michaux) Fernald; O. tetragona var. latifolia (Rydberg) Fernald

Herbs mostly glandular puberulent or glabrous, some­times strigillose or villous on stems; from fibrous rootstock. Leaves in a basal rosette and cauline, basal 3–12 × 0.5–3 cm, petiole 1–3 cm, blade oblanceolate to obovate, margins dentate to remotely denticulate; cauline 2–6(–11) × (0.5–)1–2(–5) cm, sometimes glau­cous; petiole 0.1–2(–6) cm; blade narrowly elliptic to broadly ovate, margins dentate to remotely denticulate. Flowers: buds with free tips (3–)4–8(–13) mm, connivent to spreading; floral tube 5–20 mm; sepals 8–22 mm; petals (8–)15–20(–30) mm. Capsules oblong to oblong-ellipsoid, widest at middle, (5–)10–17(–20) × (2–)3–4(–6) mm, 4-winged, sometimes 4-angled, stipe 0.1–3(–7) mm; sessile. 2n = 28.

Flowering Apr–Aug(–Sep). Open meadows, stream margins, edges of woods, open woods; (100–)300–1700 m; N.S., Ont., Que.; Ala., Conn., Del., D.C., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mich., Mo., N.H., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Va., W.Va.

Oenothera serotina Sweet (1826) is a homonym, not Lehmann (1826), while Kneiffia floribunda Spach (1835) is an illegitimate substitution based on O. tetragona, and both names pertain here.