10. Potamogeton praelongus Wulfen, Arch. Bot. (Leipzig). 3(3): 331. 1805.
白茎眼子菜 bai jing yan zi cai
Plants perennial, submerged in fresh water. Rhizome spotted, rusty red, slender or sometimes robust, often developing turions at tip. Stems terete, usually elongated, simple or sparsely branched. Stipules axillary, convolute, 1-8 cm, membranous, free from leaf base, usually persistent; leaves sessile, distichous, linear-lanceolate or lanceolate to ovate-oblong or ribbonlike, 6-25 cm, midvein conspicuous, with narrow rows of lacunae bordering midvein, base rounded to cuneate and semiamplexicaul, margin entire, apex often obtuse and markedly cucullate, splitting when pressed. Spikes cylindric, contiguous, with 6-12 whorls of opposite flowers; peduncles 5-80 cm. Carpels 4. Fruit (3.8-)4.5-5.5 mm, abaxial keel distinct; beak erect, 0.6-1 mm. Fl. and fr. Jul-Sep. 2n = 52.
Submersed in ponds or channels of still water. Heilongjiang, Jilin, Liaoning, Xinjiang, Yunnan [Japan, Kazakhstan, Mongolia, Russia; Europe, North America].