Distribution: Introduced from Washington to California, and across the southern half of the United States to the Atlantic; occasional west of the Cascades in Washington and Oregon
Habitat: Commonly used in aquaria, often escaping
Flowers: July - September
Origin: Introduced from South America
Conservation Status: Not of concern
Submersed, dioecious perennials, with sparingly-branching and nodally-rooting stems.
Stems very leafy; leaves in whorls of 4 or 6, 2.5-3 cm. long and 2-3 mm. broad, acuminate.
Both pistillate and staminate flowers with a long, thin, stipe-like tubular calyx, enclosed at the base in fused bracts; flowers 1-several in the bracts; calyx lobes 3, 4-5 mm. long, greenish; petals 5, white, twice as long as the calyx lobes; stamens 9; stigmas 3, bi-lobed.
Fruit berry-like, uncommon.