Roots to 1.5 cm, tip rounded to pointed; sheath not winged. Stipes white, small, often decaying. Fronds floating or (rarely) submersed, 1 or 2--few, coherent in groups, ovate to lanceolate, flat, thin, 1--5 mm, 1.3--3 times as long as wide, margins entire; veins 1, mostly prominent, longer than extension of air spaces, or running through at least 3/4 of distance between node and apex; with or without small papillae along midline of upper surface; anthocyanin absent; largest air spaces much shorter than 0.3 mm; turions absent. Flowers: ovaries 1-ovulate, utricular scale open on 1 side. Fruits 1--1.35 mm, not winged. Seeds with 15--29 distinct ribs. 2n = 40, 42. Flowering (very rare) spring--fall. Mesotrophic, quiet waters in temperate to tropical regions; 0--2000 m; Ala., Ariz., Ark., Calif., Conn., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Mass., Mich., Miss., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Va., W.Va., Wyo.; Mexico; West Indies (Bermuda); Central America; South America. I know of no specimens of Lemna valdiviana from Delaware, but the species is to be expected there.
Thallus flat or nearly so on both sides, usually smooth above, rather narrowly oblong, mostly 2.5-5 mm, commonly 1.5-3 times as long as wide, mostly 2-10 together, not anthocyanic, nerveless or indistinctly 1-nerved, the nerve often reaching more than 3/4 the distance from node to tip; spathe reduced, open; fr exserted, elongate-ovate, the persistent style obliquely terminal; seed solitary, oblong-ovoid, evidently ribbed; 2n=40. Widespread in the W. Hemisphere, and scattered in our range. (L. cyclostasa)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.