Glabrous, fibrous-rooted, sometimes stoloniferous, aquatic perennial. Stems erect to prostrate, flaccid, 10–50 cm. Leaves once-pinnate with 7 to 21 lanceolate to ovate, serrate to lobed leaflets 1–5 cm long; leaflets of upper leaves narrower. Umbels compound, axillary and terminal; rays 1–2 cm long; involucral and involucel bracts lance-linear, serrate 2–9 mm long. Flowers white; stylopodium low-conic; petals ca. 0.5 mm long. Mericarps hemispheric, 1–2 mm long, glabrous; ribs inconspicuous; oil tubes many in the intervals (
Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Our plants are variety
incisa (Torr.) Cronquist.