Potamogeton panormitanus Bivona; P. pusillus var. vulgaris E. M. Fries.

Plants annual, submerged in fresh water. Rhizome absent. Stems terete to slightly compressed, ca. 0.8 mm in diam., sparsely to densely branched; nodal glands absent or inconspicuous; turions markedly reduced, axillary, usually narrowly fusiform. Stipules axillary, free, 5-12 mm, connate, membranous and translucent, tubular for most of their length when young, but splitting with age, not fibrous-persistent, green or greenish brown when dry; leaves sessile, linear, 2-6 cm × 0.6-2.3 mm, 3-veined with lateral veins inconspicuous, mostly without rows of lacunae bordering midvein, midvein distinctly thickened toward leaf base, apex acute to acuminate. Spikes with 2-4 whorls of opposite flowers, lax. Carpels 4. Fruit obliquely obovoid, 1.8-2.2 mm, abaxial keel indistinct, with a short beak at tip. Fl. and fr. May-Oct. 2n = 26.

Ponds, lakes, marshes, channels, paddy fields, in still or slow-flowing water. Anhui, Fujian, Gansu, Hainan, Heilongjiang, Hebei, Henan, Hubei, Hunan, Jiangsu, Jilin, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shanxi, Sichuan, Taiwan, Xinjiang, Xizang, Yunnan, Zhejiang [Afghanistan, India, Japan (including Ryukyu Islands), Kazakhstan, Korea, Kyrgyzstan, Myanmar, Nepal, New Guinea, Pakistan, Philippines, Russia, Tajikistan, Turkmenistan, Uzbekistan; Africa, SW Asia, Europe, North America].