Perennial, subacaulescent or to 5 dm, decumbent to erect, silky-strigose; lvs linear-lanceolate, 5-10 cm, acute or acuminate, entire or nearly so, narrowed to a long petiolar base; fls few, subsessile in the axils; hypanthium slender, 7-10 cm; sep lance-linear, 2-4 cm, spreading unilaterally at anthesis and persistently connivent; pet yellow, obovate, 5-7 cm; fr 4-7 cm, slender, 4-sided, the angles bearing semi-elliptic wings 1-2.5 cm wide. Dry rocky barrens in calcareous soil; s. Ill. and Mo. to Nebr. and Colo., s. to Tex. May-July. (O. missouriensis; Megapterium missouriense)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.