Potamogeton pusillus 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 very slender, to 1.5 m, with numerous branches distally, with or without nodal glands; rhizome scarcely developed; lvs all submersed, narrowly linear, 1–7 cm × 0.2–2.5 mm, 1- or 3(5)-veined, with 0–5 rows of lacunar cells on each side of the midvein; stipular sheaths axillary, free, to 1 cm, delicate, the margins connate or merely overlapping; winter-buds commonly produced, 1–3 cm, the inner lvs rolled into a hard, fusiform structure; peduncles filiform to slightly clavate, axillary or terminal, mostly erect, 0.5–6 cm; spikes capitate to cylindric, 2–10 mm, with 1–4 whorls of fls; body of the fr ovoid to obovoid, usually plump, not keeled, 1.5–2.2 mm, the beak 0.1–0.6 mm; 2n=26. Common and widespread in both acid and alkaline waters from Nf. to Alas., s. to Fla. and Mex. Highly variable. (P. berchtoldii; P. panormitanus; P. tenuissimus) The most narrow-lvd phase, with subulate, 1-nerved lvs 0.2–0.6 mm wide, considered to be restricted to N. Engl. and s. Que., has been called var. gemmiparus Robbins. (P. gemmiparus)