Distribution: Occurring on both sides of the Cascades crest in Washington; British Columbia to California, east across most of North America to the Atlantic Coast.
Habitat: Quiet water, ponds, marshes and slow-moving streams
Flowers: July-September
Origin: Native
Growth Duration: Perennial
Conservation Status: Not of concern
Monoecious, fleshy, colonial perennials without leaves or stems, the plant a free-floating, round to obovate body 4-8 mm. long, dark green above and purplish beneath, 5- to 11-nerved; rootlets 5-15 in a cluster in the center of the body.
None
Flowers enclosed in a triangular pouch on the margin of the body; flowers 3 in each pouch, 2 staminate and 1 pistillate, the staminate a single stamen with a 2-celled anther, the ovary with 2 ovules.
Fruit a utricle.
PNW Herbaria: Specimen records of Spirodela polyrhiza in the Consortium of Pacific Northwest Herbaria database
WA Flora Checklist: Spirodela polyrhiza checklist entry
OregonFlora: Spirodela polyrhiza information
E-Flora BC: Spirodela polyrhiza atlas page
CalPhotos: Spirodela polyrhiza photos