Much like no. 14 [Oenothera fruticosa L.], and not always sharply distinct; usually only rather sparsely hairy, varying to virtually glabrous (especially below the infl), and sometimes glaucous; most of or all the hairs of the infl and fr minutely gland-tipped; lvs ovate to nearly linear, avg wider than in no. 14 [Oenothera fruticosa L.], entire or often remotely dentate, the larger ones 3-10 cm; infl and fls erect; sep-tips wholly connivent or free for 1-2 mm; pet (1-)1.5-3 cm; fr mostly 6-15 mm, thickest near or a little above the middle; 2n=28. Fields and open woods, at higher elev. than the next where their ranges overlap; N.S. and Que. to Mich., s. to n. Ga., ne. Ala., and Mo. May-Aug. (O. glauca; O. fruticosa ssp. g.; Kneiffia g.; K. hybrida; K. latifolia; K. t.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.