Twoleaf Watermilfoil

Plants hermaphroditic, occasionally monoecious. Stem stout, to 100 cm; internodes crowded. Submerged leaves 4- or 5-whorled or scattered, pectinate, oblong in outline, (1.5-)2-4 × 1-3 cm; segments in 5-12 pairs, filiform, 0.5-1.5 cm. Inflorescence a terminal spike of 4-whorled flowers, 5-35 cm, in monoecious plants lowermost flowers female, uppermost ones male; bracts persistent, eventually reflexed, lanceolate to oblong or obovate, 4-18 × 1-3 mm, margin sharply serrulate; bracteoles ovate, ca. 1.2 × 0.6 mm, margin serrate. Petals 1.5-3 mm. Stamens 4. Fruit 4-loculed, subglobose, 1-1.5 mm; mericarps with 2 finely tuberculate ridges abaxially, apex beaked. Fl. and fr. May-Aug.

Introduced and naturalized. Guangdong [native to North America].