Potamogeton pectinatus 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 3–8 dm, simple or sparingly branched below with elongate internodes, above usually flexuous, freely dichotomously branched, with internodes 1–3 cm; rhizome slender, ending in a white tuber 1–1.5 cm; lvs all submersed, narrowly linear, 3–10 cm × 0.5–1.5 mm, 1-nerved, tapering to an acute tip; stipular sheaths adnate to the blade and rather closely clasping the stem for 1–3 cm, the margins connate at least below, the free tip 2–10 mm; spikes submersed and hydrophilous, 1–4 cm, on peduncles 3–10 cm, with several whorls of fls, the lower separated; frs obliquely obovoid, 3–4.5 mm, distinctly short-beaked, rounded on the back, with a low dorsal keel only, or with 2 lateral keels only, or with 3 keels; 2n=78. Calcareous or alkaline, usually shallow water; nearly cosmopolitan, and widespread in our range. A major food for ducks.