Spirodela polyrrhiza
Linnaea 13: 392. 1839.
Roots 7–21, to 3 cm, 1 or 2 perforating scale. Fronds obovate to circular, flat or rarely gibbous, 2–10 mm, 1–1.5 times as long as wide, apex rounded or pointed, upper surface sometimes with red spot in center; veins 7–16(–21); turions sometimes present, rootless, brownish olive, circular-reniform, 1–2 mm diam. Flowers: ovaries 1–2-ovulate. Fruits 1–1.5 mm, laterally winged to apex. Seeds with 12–20 distinct ribs. 2n = 30, 38, 40, 50, 80.
Phenology: Flowering (very rare) early summer–early fall.
Habitat: Eutrophic, quiet waters, in temperate to tropical regions
Elevation: 0–2500 m
Distribution
Alta., B.C., Man., N.B., N.S., Ont., P.E.I., Que., Sask., Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., nearly worldwide.
Discussion
Selected References
None.