Spirodèle polyrhize

Lemna polyrrhiza Linnaeus, Sp. Pl. 2: 970. 1753 (as polyrhiza)

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.

Flowering (very rare) early summer--early fall. Eutrophic, quiet waters, in temperate to tropical regions; 0--2500 m; 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.