3. Lemna minor Linnaeus, Sp. Pl. 2: 970. 1753.
Roots to 15 cm, tip mostly rounded; sheath not winged. Stipes white, small, often decaying. Fronds floating, 1 or 2--5 or more, coherent in groups, ovate, scarcely gibbous, flat, 1--8 mm, 1.3--2 times as long as wide, margins entire; veins 3(--5) (if more than 3, outer ones branching from inner ones), greatest distance between lateral veins near or proximal to middle; papillae not always distinct (one near apex usually larger); lower surface very seldom slightly reddish (much less than on upper), coloring beginning from attachment point of root, upper surface occasionally diffusely reddish; air spaces 0.3 mm or shorter; distinct turions absent. Flowers: ovaries 1-ovulate, utricular scale with narrow opening at apex. Fruits 0.8--1 mm, laterally winged toward apex. Seeds with 8--15 distinct ribs, staying within fruit wall after ripening. 2n = 40, 42 (B), 50, 63, 126.
Flowering (rare) late spring--early fall. Mesotrophic to --eutrophic, quiet waters, in suboceanic, cool-temperate regions with relatively mild winters; 0--2000 m; St. Pierre and Miquelon; B.C., Ont., Que., Sask.; Ala., Ariz., Ark., Calif., Conn., Del., D.C., Fla., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis.; w Eurasia; Africa; Atlantic Islands; Australia (introduced), Australia; introduced, New Zealand (introduced).
Indication of this species in Newfoundland (H. J. Scoggan 1978--1979) probably refers to Lemna turionifera.
A specimen in the Gray Herbarium from St. Pierre and Miquelon may represent Lemna minor or L. turionifera; its determination is questionable.