Much like no. 1 [Nymphoides cordata (Elliott) Fernald], but larger and coarse, with thicker and firmer lvs 5-12 cm long and wide; stems 1.3-2.5 mm thick near the top; spur-roots seldom developed; pedicels and cal conspicuously flecked with purple; cal-lobes at anthesis 4-5 mm, at maturity reaching to or below the middle of the fr; cor 10-14 mm; fr 10-14 mm; seeds conspicuously papillate; 2n=36. Quiet water on the coastal plain; s. N.J. to Fla. and Tex. July-Sept. (N. lacunosa)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.