Annual, 1-3 dm, often branched from the base; cauline lvs linear or linear-oblong, 1-2.5 cm, sessile, those subtending the umbel narrowly lanceolate, truncate or subcordate at base, those of the umbel similar but progressively smaller; rays of the umbel 3-5; seeds gray, 1-1.5 mm, finely and rather sharply tuberculate; 2n=16, 24. Native of Europe and w. Asia, sporadically intr. and established from e. Can. to W.Va. and O. Summer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.