Fr broadly ovate to orbicular, laterally flattened, constricted at the commissure, the outer wall thickened and corky, obscuring the very narrow ribs; oil- tubes very numerous, carpophore wanting; umbels compound, terminal and lf-opposed; involucre conspicuous, of narrow bracts; umbellets 1-2 cm wide; bractlets several, narrow, sep minute or none; pet white; stylopodium conic; fibrous-rooted aquatic perennials with once- pinnate lvs, the lfls ±incised. Only the following sp.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.