Gaura biennis Linnaeus, Sp. Pl. 1: 347. 1753, not Oenothera biennis Linnaeus 1753

Herbs usually robust winter-annual, sometimes biennial, usually moderately to densely villous, rarely short-hirtellous, also glandular puberulent; from fleshy taproot. Stems usually well-branched distal to base, 50–180 cm. Leaves in a basal rosette and cauline, basal 8–20 × 1.5–3 cm, blade oblanceolate, margins irregularly toothed to lobed; cauline 1.5–12 × 0.5–3 cm, blade narrowly elliptic to elliptic or lanceolate, margins subentire or undulate-denticulate. Flowers 4-merous, zygomorphic, opening at sunset; floral tube 6–13 mm; sepals 5–13 mm; petals white, fading pink to red, narrowly elliptic-obovate, 6–12 mm; filaments 5–10 mm, anthers 2–4 mm, pollen 35–65% fertile; style 12–15 mm, stigma surrounded by anthers. Capsules ellipsoid, 4-angled, 5–9 × 2–3 mm; sessile. Seeds 3–6, light to reddish brown, 2–2.5 × 1–1.3 mm. 2n = 14.

Flowering Jun–Oct. Open woods, fields, along streams, disturbed sites, ditch banks, roadsides, railway embankments; 100–600 m; Ont., Que.; Conn., Del., D.C., Ill., Ind., Iowa, Ky., Md., Mass., Mich., Minn., N.J., N.Y., N.C., Ohio, Pa., Tenn., Vt., Va., W.Va., Wis.

Oenothera gaura is a PTH species and forms a ring of 14 chromosomes in meiosis. It is self-compatible and autogamous (P. H. Raven and D. P. Gregory 1972[1973]), and may have been derived from O. filiformis.