Slender, 3-7 dm, branched above; lvs 3-10 cm, pinnately dissected into filiform segments 1-6 cm, the primary divisions alternate or opposite on the rachis; petiole to 1 cm, winged its whole length; umbels 2-6 cm wide; bracts filiform, usually entire; rays 15-30, slender, 1-3 cm; fr subglobose, 1.5 mm; styles 0.5-1.5 mm, strongly recurved at maturity; 2n=14. Wet soil; Tex. and La. to Kans. and Mo., almost entirely s. of the Missouri R. June, July.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.