8. Potamogeton berchtoldii Fieber in Berchtold & Opiz, Oekon.-techn. Fl. Böhm. 2: 40. 1838.
纤细眼子菜 xian xi yan zi cai
Potamogeton berchtoldii var. tenuissimus (Mertens & W. D. J. Koch) Fernald; P. pusillus Linnaeus var. berchtoldii (Fieber) Nyman; P. pusillus subsp. tenuissimus (Mertens & W. D. J. Koch) K. Richter; P. pusillus var. tenuissimus Mertens & W. D. J. Koch.
Plants annual, submerged in fresh water. Rhizome absent. Stems filiform, subsimple to freely branching; a pair of nodal glands conspicuously present; turions shortened, shootlike, terminal. Stipules axillary, convolute, fused throughout side toward leaf, 3-14 mm, membranous and translucent, flat or with inrolled margins, not fibrous-persistent; leaves sessile, linear, mostly broad, parallel-sided, 0.8-8.5 cm × 0.3-2.4 mm, 3-veined, with conspicuous lacunae bordering midvein, midvein not thickened toward leaf base, base rounded, apex obtuse or subacute to acute. Spikes in 1-3 whorls of opposite flowers, lax, 4-8 mm in fruit. Carpels 4. Fruit obliquely obovoid, 2-2.5 mm, rounded on back, with short beak tip. Fl. and fr. May-Oct. 2n = 26.
Ponds, lakes, marshes, ditches. Hebei, Heilongjiang, Shanxi, Yunnan [Bhutan, Japan, Korea, Russia; SW Asia, Europe, North America].