Description from Flora of China
Potamogeton serrulatus Regel & Maack.
Plants perennial, submerged in fresh water. Rhizomes present, terete. Stems creeping at base or even to lower part, slender, terete to slightly compressed, ca. 1 mm diam., richly branched; turions absent. Stipules 3-6 mm, adnate to and slightly fused with leaf base, convolute, membranous; leaves sessile, broadly linear, 2-6 cm × 2-4 mm, 3-7-veined, lateral veins faint, with narrow rows of lacunae bordering midvein, base rounded, margin serrulate, apex obtuse to rounded. Spikes usually few flowered, with only 2 or 3 whorls of contiguous or shortly distant opposite flowers; peduncles 1-4 cm. Carpels usually 4. Fruit obovoid, 3.5-4 mm, abaxial keel distinct, with a short beak ca. 0.5 mm at tip. Fl. and fr. Jun-Sep.
Lakes, ponds, rarely in rivers, usually in slightly acid water. Anhui, Hebei, Heilongjiang, Hubei, Jiangsu, Jilin, Liaoning, Shaanxi, Shandong, Sichuan, Taiwan, Yunnan, Zhejiang [Indonesia (Sumatra), Japan, Korea, Philippines, Russia (Siberia)].