Oenothera rhombipetala Nutt.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Much like no. 6 [Oenothera clelandii W. Dietr., P. H. Raven & W. L. Wagner], but an out crossing diploid with larger fls, the hypanthium 2–3.5 cm, the sep 1.5–2.5 cm, the pet 1.5–2.5(3) cm, often rhombic- obovate. Fields and prairies in sandy soil; Great Plains, from S.D. to Okla. and Tex., e. occasionally at least as far as se. Minn. June–Sept. (Raimannia r.)