Potamogeton pusillus
Gerald D. Carr

Flora of Oregon

Stems terete to slightly compressed, 18– 150 cm; nodal glands present on at least some nodes, to 0.5 mm diameter, green, gold, brown, or rarely white.

Leaves submersed, attached to stem nodes, not attached to stipules; stipules connate, 3.1–9.2 mm, rarely fibrous, tip obtuse; blades linear, 14–65 × 0.5–1.9 mm; base slightly tapering; margins entire; tip acute or rarely apiculate, rarely with a bristle; lacunae in 0–2 rows on each side of midrib; veins 1–3.

Inflorescences submersed or emersed; spikes cylindric, interrupted, 1.5–10.1 mm; peduncles 1–3 per plant, axillary or terminal, filiform to cylindric, erect, rarely recurved, 5–66 mm.

Fruits sessile, obovoid, sides centrally concave, 1.5–2.2 × 1.2– 1.6 mm, green to brown, not keeled; beaks erect, displaced ventrally or rarely at middle of fruit tip, 0.1–0.6 mm.

Streams, lakes, marshes. 0–1600 m. BR, BW, Casc, CR, ECas, Est, Lava, Sisk, WV. CA, ID, NV, WA; north to Northwest Territories, east to CT, southeast to AZ and FL, South America; Africa, Eurasia. Native.

Immature plants usually cannot be distinguished from P. foliosus or P. berchtoldii.

Flora of North America

as described under Potamogeton pusillus

Rhizomes absent. Cauline stems terete to slightly compressed, without spots, 18--150 cm; glands present on at least some nodes, green, gold, brown, or rarely white, to 0.5 mm diam. Turions common, soft, lateral or terminal, 0.9--3.2 cm ´ 0.3--1.8 mm, soft; leaves ± 2-ranked; outer leaves 1--3 per side, base not corrugate, apex subulate to obtuse; inner leaves rolled into hardened fusiform structure. Leaves submersed, ± spirally arranged, sessile, delicate to coarse; stipules persistent, inconspicuous, connate or convolute, free from base of blade, brown to green or white, not ligulate, 0.31--0.92 cm, rarely appearing fibrous, not shredding at tip, apex obtuse; blade pale green to olive-green, rarely somewhat reddish, linear, not arcuate, 0.9--6.5 cm ´ 0.2--2.5 mm, base slightly tapering, without basal lobes, not clasping, margins entire, not crispate, apex not hoodlike, subulate to obtuse, lacunae absent or present, in 0--5 rows each side of midrib; veins 1--3(--5). Inflorescences unbranched, submersed or emersed; peduncles not dimorphic, axillary or terminal, erect, rarely recurved, filiform to slightly clavate, 0.5--6.2(--6.6) cm; spikes not dimorphic, capitate to cylindric, 1.5--10.1 mm. Fruits sessile, green to brown, ovoid to obovoid, turgid to concave, not abaxially or laterally keeled, 1.5--2.2 ´ 1.2--1.6 mm; beak erect, 0.1--0.6; sides without basal tubercles; embryo with less than 1 full spiral.Three hybrids, Potamogeton perfoliatus ´ P. pusillus (= P. ´ mysticus Morong), P. friesii ´ P. pusillus (= P. ´ pusilliformis Fisher [P. ´ intermedius Fischer]), and P. obtusifolius ´ P. pusillus (= P. ´ saxonicus Hagström), have been described.

Photo images

/imglib/misc/201801/DIG44847_1516993341_tn.jpg
/imglib/misc/201801/DIG44848_1516993281_tn.jpg
/imglib/misc/201801/DIG44844_1516993365_tn.jpg
/imglib/misc/201801/DIG44843_1516993307_tn.jpg
/imglib/misc/201801/DIG44845_1516993276_tn.jpg

Herbarium specimens

https://botanydb.colorado.edu/botany/COLO_V/02362/02362259_tn.jpg
https://www.pnwherbaria.org/images/thumbnail.php?Image=WTU-V-023238.jpg
https://www.pnwherbaria.org/images/thumbnail.php?Image=WTU-V-023567.jpg
https://www.pnwherbaria.org/images/thumbnail.php?Image=WTU-V-006945.jpg
https://www.pnwherbaria.org/images/thumbnail.php?Image=WTU-V-035422.jpg