Distribution: Chiefly west of the Cascades in Washington; Washington south to California, east to Idaho and Montana.
Habitat: In ponds and lakes.
Conservation Status: Threatened in Washington (WANHP)
Aquatic, annual herbs, the plants rooted, the stem naked below and branched above, the branches spreading or floating, the whole plant green and glabrous, 1-6 dm. long.
Leaves numerous, alternate or whorled in threes, linear or filiform, entire, 1-4.5 cm. long and up to 1.5 mm. wide.
Flowers 3-10, axillary, scattered, the pedicels stout, 1-4 mm. long, merging with the base of the capsule; calyx lobes 5, 1.5-7 mm. long; corolla two-lipped, 2-2.7 mm. long, green, the tube deeply cleft dorsally, or the flowers apetalous; ovary inferior.
Fruit a thin-walled, 1-celled capsule, 5-13 mm. long and 1-2 mm. thick, with a few large, shiny, brown seeds.