4. Stuckenia pectinata (Linnaeus) Börner, Fl. Deut. Volk. 713. 1912.
蓖齿眼子菜 bi chi yan zi cai
Potamogeton pectinatus Linnaeus, Sp. Pl. 1: 127. 1753; Coleogeton pectinatus (Linnaeus) Les & R. R. Haynes; P. bracteatus Y. D. Chen; P. erhaiensis Y. D. Chen; P. interruptus Kitaibel; P. intramongolicus Y. C. Ma; P. leptanthus Y. D. Chen; P. miniatus Y. D. Chen; P. nanus Y. D. Chen; P. pectinatus var. diffusus Hagström; P. pectinatus var. interruptus (Kitaibel) Ascherson.
Plants perennial, submerged. Rhizome slender to robust, terete, usually developing apical buds. Stems sparsely to densely branched, filiform to slender, terete, 0.5-4 mm in diam. Stipules partly fused with leaf base and sheathing stem; sheaths 1-6.5 cm, convolute, appearing as a short spiral when transversely dissected, persistent, usually green with greenish to pale brownish margins; leaves sessile, usually olive-green to dark green, mostly ± straight, filiform to linear, 2-12 cm × 0.2-4 mm, 3-5-veined, lateral veins inconspicuous, usually with air channels bordering midvein, apex acuminate to acute, occasionally obtuse or rounded with short mucro. Spikes cylindric, 1-6 cm, with 3-7 whorls of opposite flowers, contiguous at first, later inconspicuously or conspicuously distant; peduncles elongated, slender, ca. as thick as stem. Carpels 4. Fruit obovoid, 3.4-4.2 mm, abaxial keel indistinct, with short beak. Fl. and fr. May-Oct. 2n = 78.
Submerged in fresh water or brackish lakes, ponds, rivers, channels, and marshes. Anhui, Fujian, Gansu, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Jiangsu, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Taiwan, Xinjiang, Xizang, Yunnan, Zhejiang [Afghanistan, Bangladesh, India, Indonesia (Sumatra), Japan, Kazakhstan, Korea, Kyrgyzstan, Mongolia, Myanmar, Nepal, Pakistan, Philippines, Russia, Sri Lanka, Tajikistan, Turkmenistan, Uzbekistan; Africa, SW Asia, Australia, Europe, North and South America, Pacific islands].
Stuckenia pectinata is an extremely polymorphic species with numerous forms depending on geographical and ecological circumstances.