Stems often much elongate, green, very slender, near the summit less than 1 mm thick; lf broadly ovate, deeply cordate, 3-7 cm; functionally dioecious, some fls usually replaced by spur-like tuberous-thickened roots; cal-lobes at anthesis 2-3 mm, in fr extending well beyond the middle of the capsule; cor 5-8 mm, white or creamy, with a crest- like yellow gland at the base of each lobe; anthers ca 1 cm or less; fr 4-5 mm, not beaked; seeds smooth or sparsely papillate; 2n=36. In quiet water; Nf. and Que. to Ont., s. to Conn. and N.Y., and locally along the coastal plain to Fla. and La. July-Sept. (N. lacunosa, misapplied)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.