Myriophyllum oguraense Miki

Plants monoecious. Stems branched mainly at base. Submerged leaves 4- or 5-whorled, pectinate, ovate to suborbicular in outline, 2.4-5.7 × 2.3-5.5 cm; segments in 9-13 pairs, filiform, 1-3 cm; emergent leaves smaller. Inflorescence a simple or sometimes 2-10-branched spike of 4-whorled flowers; main and lateral inflorescences 2.5-9.5 cm; bracts leaflike; bracteoles white, 3-fid to pectinate. Male flowers: sepals green, deltoid, 0.5-0.8 mm; petals white to pale green, hooded, weakly keeled at base, caducous; stamens 8. Female flowers: sepals green, deltoid, 0.4-0.6 mm; petals white, slightly hooded, caducous; stigmas pinkish after anthesis, shortly fimbriate. Fruit olive-brown, 4-loculed, shortly cylindric; mericarps smooth with 2 abaxial, longitudinal ridges. Fl. and fr. Apr-Sep.

Slow-flowing tributaries of the Chang Jiang basin. Anhui, Heilongjiang, Hubei, Jiangsu, Jiangxi, Zhejiang [Japan].