3. Najas gracillima (A. Braun ex Engelmann) Magnus, Beitr. Kenntn. Najas. 23. 1870.
纤细茨藻 xian xi ci zao
Najas indica (Willdenow) Chamisso var. gracillima A. Braun ex Engelmann in A. Gray, Manual, ed. 5, 681. 1867; N. japonica Nakai.
Stems 8-20 cm tall, 0.3-0.5 mm in diam. Leaves often in pseudowhorls of 5, ca. 2 cm × 0.3-0.5 mm; sheath 1-2 mm; auricles orbicular to slightly obcordate, short, minutely serrulate with 6 or 7 teeth, upper margin on each side minutely serrulate with 7-11 teeth. Plants monoecious; flowers 1-4 per axil, male flowers in upper axils and female ones throughout. Male flowers elliptic, 1-1.5 mm; spathe with a short neck, with brownish spine cells at apex; anther 1-thecous. Female flowers conspicuous, 2-3 mm; style 1-2 mm; stigmas 2-lobed. Fruit linear-ellipsoid, 2-3 × ca. 0.5 mm. Seeds narrowly ellipsoid, with more than 20 rows of pits; areoles oblong, longitudinally elongated. Fl. and fr. Jun-Aug. 2n = 12, 24.
Paddy fields, shallow water of ponds and channels; below 1800 m. Fujian, Guangxi, Guizhou, Hainan, Hebei, Hubei, Jiangxi, Jilin, Liaoning, Nei Mongol, Taiwan, Yunnan, Zhejiang [Japan; North America].
Najas gracillima is most similar to N. minor, especially in vegetative condition. However, N. gracillima can be separated from N. minor by its fruit often straight and the areoles of its seeds longer than broad.