Stem mainly submersed, to 1 m or more; blades of aerial lvs 2-5 cm wide, sharply serrate above; fls axillary, short-peduncled; pet white, 8 mm; fr 3-4 cm wide, with 4 stout horns; 2n=ca 36, ca 48. Native of Eurasia, established and becoming abundant in the Hudson, Potomac, and Mohawk rivers, and locally elsewhere in our range. June-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.