Compilation
Potamogeton parvifolius

Aquatic herb with submerged and floating leaves; rhizomes absent or present, annual or perennial, poorly developed, filiform, terete; stems annual, 20– 100 cm long, sparingly or much branched, filiform, terete with grooves, sometimes developing axillary tubers. Submerged leaves bright green to brown-green, sessile, linear, 25– 55(– 75) mm long, 0.5– 1.2(– 3) mm wide, 30– 75 times as long as wide, entire at margins, acute to acuminate, 3-veined; midrib bordered with broad rows of lacunae; lateral veins sometimes inconspicuous; intermediate leaves often present, petiolate, oblong to lanceolate; floating leaves present or absent, petiolate; petiole 3– 25(– 34) mm long, 0.2– 1.1 times as long as the lamina; lamina narrowly lanceolate toelliptical or oblong,(5– )9– 29(– 38) mm long, (2– )3– 11 mm wide, 1.3– 6(– 8.5) times as long as wide, opaque, coriaceous to subcoriaceous, bright green to dark green, sometimes with a brownish tinge, 5– 7-veined, cuneate at base, acute at apex; margins entire; stipules axillary, convolute, 4– 13 mm long, translucent, decaying early. Inflorescences developing mostly in the axils of floating leaves; peduncles 9– 20(– 40) mm long, 0.7– 2.4 times as long as the fruiting spike, as thick or slightly thicker than the stem; spikes cylindrical, 5– 16 mm long when in fruit, with 7– 9 flowers in 3– 7 contiguous or shortly distant whorls. Tepals broadly ovate, ± 1 mm long, green; carpels (3– )4(– 7). Fruitlets 1.5– 2.4(– 3.5) mm long, green; beak short to fairly long, hooked; dorsal keel mostly distinct, crenulate. Stem anatomy: stele of the oblong or the circular type; endodermis of O-type; interlacunar bundles absent, rarely a few present; subepidermal bundles present; pseudohypodermis absent or present, 1-layered.