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, obovate, flat or gibbous, 1--3.5 mm, 1--1.5 times as long as wide, margins entire; veins 3, greatest distance between lateral veins near middle; very distinct papillae near apex, some smaller indistinct ones on midline of upper surface; lower surface very often red colored (more intensely than on upper), coloring beginning at attachment point of root, lower upper surface sometimes with red spots; air spaces shorter than 0.3 mm; distinct turions absent. Flowers: ovaries 1-ovulate, utricular scale with narrow opening at apex. Fruits 0.5--0.7 mm, not winged. Seeds with 10--16 distinct ribs, staying within fruit wall after ripening. 2n = 40, 42, 50.
Flowering (occasional) spring--fall. Mesotrophic to --eutrophic, quiet waters, in temperate to subtropical regions with mild winters; 0--800 m; Ala., Ark., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Minn., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Tex., Va., Wis.; c Mexico; South America (Colombia, Ecuador); Hawaii.
Aquatic herb Flowers: occurring occasionally, lacking sepals and petals, with two stamens, surrounded by a membraneous scale with a narrow opening at the tip. Fruit: bladder-like (utricle), thin-walled, 0.5 - 0.7 mm long, unwinged, with seeds having ten to sixteen distinct ribs. Seeds emain inside the fruit wall after ripening. Roots: to 15 cm, tip rounded in hydrated specimens but pointed in dried specimens. Plant body: not differentiated into stem and leaves, floating or near surface, one to five or more attached, green sometimes with red spots above, red to purple beneath with color beginning at root attachment, 1 - 3.5 mm long, one to one and a half times as long as wide, flat or swollen on one side (to 2.5 mm thick), rounded to inversely egg-shaped with a thin margin often curling upward, often three-veined, with a very distinct projection near the tip with other tiny projections along the midvein. Air spaces inside the plant body are shorter than 0.3 mm.
Similar species: Lemna minuta, Lemna obscura, and Lemna valdiviana are usually less than 1.5 mm wide and are veinless, single- or three-veined. Lemna minuta has a green plant body that is veinless or single-veined and the margin does not curl upward, while Lemna valdiviana has a green, single-veined plant body that is elliptic to narrow oblong with an asymmetrical base.
Flowering: spring to fall
Habitat and ecology: Quiet waters.
Occurence in the Chicago region: native
Etymology: Lemna is the Greek name for a water weed. Obscura means hidden.