Distribution: British Columbia to Newfoundland, south on both sides of the Cascades to Mexico.
Habitat: Standing to moving, shallow water.
Flowers: Late June - August
Conservation Status: Not of concern
Aquatic, herbaceous perennials from slender rhizomes, the stems freely branching, somewhat compressed and narrow winged, scarcely 1 mm. broad, up to 10 dm. long.
Leaves all submersed, without basal glands, narrowly linear, 1-1.5 mm. broad and up to 10 cm. long, acute, 3-nerved, bordered toward the base with air chambers; stipules united and surrounding the stem, 5-15 mm. long, ultimately disintegrating.
Inflorescence of spikes up to 5 mm. long with 2-3 whorls of crowded, sessile flowers; peduncles stout, rarely over 2 cm. long; perianth of 4 clawed segments, each with an upturned, oval blade; stamens 4, fused with the claws; pistils 4, sessile.
Achenes obliquely obovoid, 2 mm. long, with a prominent dorsal keel.