Welwitsch, Bol. Ann. Cons. Ultramar. (Portugal). 55: 578. 1859.
Lemna paucicostata Hegelmaier
Roots to 3 cm; tip usually sharp pointed; sheath winged at base (wing 1--2.5 times as long as wide). Stipes small, white, often decaying. Fronds floating, 1 or 2--few, coherent in groups, ovate-lanceolate, flat, 1--6 mm, 1--3 times as long as wide, margins entire; veins 3, greatest distance between lateral veins near or proximal to middle; 1 often very distinct papilla near apex on upper surface and 1 above node; anthocyanin absent, no reddish color; largest air spaces much shorter than 0.3 mm; distinct turions absent. Flowers: ovaries 1-ovulate, utricular scale open on 1 side. Fruits 0.5--0.8 mm, not winged. Seeds with 8--26 distinct ribs, falling out of fruit wall after ripening. 2n = 40, 42, 50, 60, 80, 84.
Flowering (frequent) spring--fall. Mesotrophic to eutrophic, quiet waters in warm-temperate to tropical regions; 0--1300 mm; Ala., Ariz., Ark., Calif., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Miss., Mo., Nebr., N.Mex., N.C., Okla., S.C., Tenn., Tex., Va., Wis.; West Indies; Central America; South America; s Eurasia; Africa; Atlantic Islands; Indian Ocean Islands; Pacific Islands; Australia.
Some authors did not distinguish between Lemna aequinoctialis and L. perpusilla and used the latter name for both species.