Rhizomes absent. Cauline stems terete, without spots, 2--5 cm; glands absent. Turions common, axillary, 0.5--2 cm ´ 0.5--1.2 mm, soft; leaves ± 2-ranked; outer leaves 2--3 per side, base not corrugate, apex acute; inner leaves undifferentiated or rolled into tight, hardened structure. Leaves submersed, or both submersed and floating, ± spirally arranged. Submersed leaves sessile, delicate; stipules persistent, inconspicuous, convolute, free from blade, green to brown, not ligulate, 0.4--1.2 cm, not fibrous, not shredding at tip, apex attenuate; blade light green, linear-filiform, not arcuate, 2--8 cm ´ 0.1--1 mm, bases slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, acute to almost bristle-tipped, lacunae present, rarely absent, 0--2 rows each side of midvein; veins 1(--3). Floating leaves: petioles continuous in color to apex, 5--25 mm; blade adaxially greenish brown, elliptic, spatulate, or obovate, 0.6--1.5 cm ´ 3--8 mm, base acute, apex obtuse; veins 5--9. Inflorescences unbranched, emersed; peduncles not dimorphic, terminal, ascending in flower, recurved in fruit, cylindric, 5--30 mm; spikes not dimorphic, cylindric or moniliform, 6--8 mm. Fruits sessile, green to brown, obliquely round-obovoid, compressed, abaxially keeled, not laterally keeled, 1.5--2.5 ´ 1.2--1.6 mm; beak erect, 0.3--0.5 mm; sides without basal tubercles; embryo with 1 full spiral. 2n = 28.
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thin and transparent, narrowly linear, 2–6 cm × 0.2–1 mm, sharply acute, 1-nerved or rarely with 2 weak lateral nerves, without lacunar cells; stipular sheaths free, linear, scarcely encircling the stem, 4–10 mm, scarious, weakly fibrous in age; floating lvs rather sparingly produced on at least some plants of a colony, the blade spatulate to obovate, 8–15 mm, 5–9-veined, the spaces between the veins filled by minute, elliptic lacunar cells, the petiole ca as long as the blade; winter-buds 1–3 cm, the inner lvs rolled into a hard, fusiform structure; peduncles slender, 0.5–3 cm; spikes cylindric, 3–8 mm, with 1–4 ± contiguous whorls of fls; fr obovoid, 1.5–2.5 mm, with flat or shallowly pitted sides, with or without a low, rounded dorsal keel; 2n=28. In quiet water; N.B. and s. Que. to Minn., s. to Pa., O., and Ill. (P. lateralis, the name based on a mixture of P. pusillus and P. vaseyi)
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