3. Potamogeton compressus Linnaeus, Sp. Pl. 1: 127. 1753.
扁茎眼子菜 bian jing yan zi cai
Potamogeton zosterifolius Schumacher.
Plants annual, submerged in fresh water. Rhizome absent. Stems densely branched, internodes slightly to strongly compressed, 1.2-3.5 mm wide; nodal glands absent; turions axillary or terminal, shortened shootlike, leafy. Stipules axillary, convolute, 1-1.8 cm, translucent, often fibrous-persistent at apex; leaves sessile, linear, 5-15 cm × 2.4-4.8 mm, 3-5-veined with 12-32 sclerenchymatous strands faint but visible, with narrow rows of lacunae bordering midvein, base narrowly cuneate, apex subacute to rounded and mucronate. Spikes 1.6-3.3 cm in 4-7 whorls of opposite flowers, contiguous, cylindric; peduncles 2.5-6 cm. Carpels usually 2. Fruit subrounded, 3.4-4.6 mm, abaxial keel distinct, beak slightly curved toward back. Fl. and fr. Jul-Sep. 2n = 26.
Lakes, ponds, channels. Yunnan [Japan, Kazakhstan, Mongolia, Russia; boreal and temperate regions of Asia and Europe].
This species was also reported from NE China; however, those records may have been based on misidentifications of Potamogeton mandschuriensis.