Robust, to 1.5 m, branched above; lvs 5-15 cm, pinnately dissected into innumerable filiform segments 5-10 mm, the primary divisions verticillate along the rachis; petiole well developed, the stipular wings none or barely developed at the base only; umbels long-pedunculate, 4-8 cm wide; bracts usually filiform and undivided; rays 12-30, 2-4 cm, fr broadly ovoid, 3-3.5 mm; styles 1.5-3 mm, spreading; 2n=22, 32. Swamps and wet woods; irregularly from s. Ill. and Mo. to N.C., Ga., and Tex. July-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.