Stems slender, 3–10 dm, not much thickened at base and sometimes without thickened roots; lvs all cauline, with linear or very narrowly lanceolate, sparsely and saliently dentate to entire lfls or segments to 5 mm wide; umbels rarely to 5 cm wide, often none, surpassed by the leafy shoots; fr rarely matured, orbicular, 1.5–2 mm, the lateral ribs separated by a constriction at the commissure; 2n=22. Swamps and marshes; Nf. to Alas., s. to Pa., W.Va., Ky., Kans., and Oreg., and at higher altitudes to Va. July–Sept.
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