6. Potamogeton friesii Ruprecht, Beitr. Pflanzenk. Russ. Reiches. 4: 43. 1845.
弗里斯眼子菜 fu li si yan zi cai
Potamogeton mucronatus Schrader ex Sonder (1850), not C. Presl (1851); P. pusillus Linnaeus subsp. friesii (Ruprecht) J. D. Hooker.
Plants annual, submerged in fresh water. Rhizome absent or present. Stems filiform, compressed, sparsely to densely branched; nodal glands present; turions terminal or axillary, composed of 2 or 3 outer leaves and a fan-shaped structure from stipules oriented at 90° to leaves. Stipules 7-25 mm, fused at base, but at upper portion split into 2 remnants, fibrous, creamy white when dry; leaves sessile, linear, 2.3-6.5 cm × 1.2-3.2 mm, (3-)5(-7)-veined, lacunae lacking or 1 narrow row per side of midvein, apex mucronate. Spike with 4-8 flowers, 7-16 mm in fruit. Carpels 4. Fruit obovoid, 1.8-2.5(-3) mm, lacking keel; beak erect, 0.3-0.7 mm. Fl. and fr. Jun-Aug. 2n = 26.
Ponds, lakes, streams. Nei Mongol [Kazakhstan, Russia, Tajikistan; Europe, North America].