Slender, 2-6 dm; lvs firm, lance-ovate to oblong or elliptic, 3-6(-10) cm, cuneate to rounded at base, finely hairy beneath; petioles 2-8 mm; umbels solitary and terminal, or 1 or 2 lateral, loosely few-fld; cor greenish-white to greenish-purple, its lobes 5-7 mm; hoods as in no. 7 [Asclepias syriaca L.], even in size; pods merely thinly hairy; 2n=22. Dry prairies; n. Ill. to Wis., Minn., s. Sask., and w. S.D. June, July.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.