15. Potamogeton gramineus Linnaeus, Sp. Pl. 1: 127. 1753.
禾叶眼子菜 he ye yan zi cai
Potamogeton heterocaulis Dia; P. heterophyllus Schreber.
Plants perennial, in fresh water. Rhizome slender to slightly robust, usually densely branched, with apical dormant buds. Stems terete, 1-2 mm in diam., usually densely branched, sometimes sparsely branched. Leaves dimorphic; stipules axillary, convolute, conspicuous, 6-35 mm, herbaceous or membranous, amplexicaul. Submerged leaves sessile, translucent, linear-oblong to oblanceolate, 3-5 cm × 5-12 mm, herbaceous, (3-)5-9(-13)-veined, base cuneate, margin ± minutely denticulate, apex mucronate. Floating leaves present or absent, petiolate; petiole usually longer than blade; blade opaque, elliptic or ovate-elliptic to elliptic-lanceolate, (7-)11-21(-23)-veined, leathery, base cuneate or rounded, margin entire, apex obtuse. Spikes cylindric, 15-40 mm, densely flowered, with many whorls of opposite flowers; peduncles 4-7 cm, thickened upward. Carpels 4. Fruit obovoid, 2.4-3.1 mm, abaxial keel obtuse, with a short beak at tip. Fl. and fr. Jul-Sep. 2n = 52.
Ponds, marshes, channels. Heilongjiang, Jilin, Liaoning, Nei Mongol, N Shaanxi, Sichuan, Xinjiang, Xizang, Yunnan [Japan, Kazakhstan, Korea, Mongolia, Pakistan, Russia, Turkmenistan, Uzbekistan; SW Asia (Iran), Europe, North America].