Fibrous-rooted from a very short erect crown; stem solitary, angular, stout, to 2 m; principal lvs with 7-17 linear to lance-ovate lfls 5-10 cm, sharply serrate, the primary lateral veins bearing no obvious relationship to the teeth or sinuses; submersed lvs, if present, bipinnately dissected; umbels 3-12 cm wide; bracts and bractlets usually 5 or 8; fr oval, 2-3 mm, nearly as wide; carpophore wanting; 2n=12. Sunny wet meadows and swamps; Nf. to Alas. and Siberia, s. to Fla. and Calif. July-Sept. (S. floridanum, a lax shade-form; S. carsonii, a lax aquatic form with few lfls or even simple lvs)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.