in War Department [U.S.], Pacif. Railr. Rep. 4(5): 135. 1857.
Leaves connate at base, narrowly spatulate, 3.5–7.1(–7.2) × 0.7–1.4 mm, 1+-veined. Stem and leaf scales present. Inflorescences: bracts absent. Pedicels 1.2–3.3 mm in fruit. Flowers usually 1 pistillate and 1 staminate in each axil, sometimes 1 or 2 axils with 2 pistillate, rarely solitary; styles sharply deflexed; pollen yellow. Schizocarps 0.7–0.9 × 1.1–1.4 mm, shorter than wide; mericarps maroon or white, not swollen, winged throughout, wings straight, 0.1–0.2 mm wide. 2n = 20.
Phenology: Flowering Apr–Aug.
Habitat: Lakes, reservoirs, floodplain pools, streams, vernal pools.
Elevation: 0–1000 m.
B.C., Calif., Oreg., Mexico (Baja California).
Callitriche marginata is known throughout the California floristic province northward to southeastern British Columbia. There are no records from Washington State and British Columbia; occurrences may be remnants of a previously more widespread population (M. Miller 2001).