Coarse, single-stemmed, fibrous-rooted annual or biennial 1.5-15 dm; pubescence spreading, crisp-villous, commonly persisting in large part until flowering time or beyond, especially in the infl; lvs entire or coarsely toothed, scarcely pinnatifid, rather equably distributed, 3-20 נ0.5-4.5 cm, the lower petiolate and often soon deciduous, the upper becoming sessile and ±clasping; heads several or numerous in an often congested infl, the disk 7-14 mm wide, or larger in fr; invol 7-10 mm, its bracts ca 21, very thin and generally pale, commonly with darker base; rays pale yellow, 4-9 mm; pappus accrescent, very fine and copious; achenes glabrous; 2n=48. Swamps and edges of ponds; circumpolar, s. in our range to Minn. and extreme n. Io. June-Aug. (S. palustris, a preoccupied name)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.