Perennial to 6 dm, usually with clustered stems, often somewhat woody below, generally strigose-canescent at least above; lvs numerous, linear to narrowly oblong or oblanceolate, 2-6 cm, entire or more often sharply serrulate; fls sessile in the upper axils, matutinal, autogamous; hypanthium funnelform, 3-12 mm, 4-angled, ±pubescent, sometimes only on the angles; sep triangular-ovate, with sharply raised midrib, reflexed at anthesis; pet yellow, 5-12 mm; stamens 8, alternately unequal; style only shortly or scarcely surpassing the hypanthium; stigma discoid, slightly 4-lobed; fr linear, canescent, roundly 4-angled, 1.5-3 cm; seeds 1.5 mm, sharply angled; 2n=14, a complex heterozygote. Dry prairies and plains; Wis., w. Mich., and Minn. to Alta., s. to Ill., Ark., Tex., Ariz., and Chih. June, July. (Oenothera s.; Meriolix s.; M. intermedia)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.