Erect, 2-6 dm, commonly branched above the middle only; rays 5-11, strongly ascending, 2-15 mm, very unequal; pedicels 2-6, unequal, to 6 mm or those of the central umbellets sessile; fr 1.5-2 mm, tuberculate; 2n=22. Dry or moist sandy soil; Tex. and n. Mex., e. to Neb. and s. Ill., and occasionally adventive farther e. May, June. (S. patens)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.