丝叶眼子菜 si ye yan zi cai

Potamogeton filiformis Persoon, Syn. Pl. 1: 152. 1805; Coleogeton filiformis (Persoon) Les & R. R. Haynes; P. applanatus Y. D. Chen; P. filiformis var. applanatus (Y. D. Chen) Q. Y. Li; P. rostratus Hagström.

Plants perennial, submerged. Rhizome terete, slender, with apical dormant buds. Stems slender, terete to compressed, ca. 0.5 mm in diam., sparsely to densely branched at base. Stipules partly fused with leaf base and sheathing stem; sheaths 0.6-4 cm, on vegetative branches 0.3-1.8 mm in diam., connate, tubular toward base at least when young, appearing as a closed ellipse when transversely dissected, persistent; leaves sessile, filiform, 3-18 cm × 0.2-1.2(-1.6) mm, 3-veined, lateral veins inconspicuous, with air channels bordering midvein, apex obtuse to bifurcate. Spikes terminal, with 3-6 whorls of opposite flowers, markedly distant even at anthesis; peduncles 4-20 cm, slender. Carpels 4. Fruit obovoid, 1.9-2.6(-3) mm, abaxial keel indistinct, obtuse, beak very short, verruciform. Fl. and fr. Jul-Oct. 2n = 78.

Lakes, ponds, marshes. Gansu, Nei Mongol, Qinghai, Shaanxi, Sichuan, Xizang, Yunnan [Afghanistan, Bhutan, Kyrgyzstan, Mongolia, Nepal, Pakistan, Russia, Tajikistan, Uzbekistan; SW Asia, Europe, North and South America].