Potamogeton natans L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Stems 1–2 m, simple or sparingly branched; submersed lvs petiole-like, narrowly linear, 1–4 dm × 1–2 mm, with 3–5-obscure veins; floating lvs elliptic or elliptic- ovate, 5–10 × 2–4.5 cm, obtuse or bluntly short-cuspidate, rounded or subcordate at base, many-nerved; petiole usually much exceeding the blade and flexibly attached to it; stipules axillary, free, 4–10 cm, acute; peduncles 8–15 cm, usually thicker than the stem; spikes dense, cylindric, 2–5 cm; frs obovoid, turgid, with a rather loose, shiny pericarp, 3.5–5 mm, deeply wrinkled on each side, not keeled, or with an obscure dorsal keel; 2n=52. Ponds and slow streams; circumboreal, s. in Amer. to Pa., Ind., Io., and Calif.