Fronds boat-shaped, 0.5--1.6 mm, 1--1.5 times as long as wide, 0.3--0.7 times as deep as wide, rounded at apex, papilla usually prominent in center of upper surface (tent-shaped); upper surface intensely green, with 50--100 stomates; pigment cells present in vegetative tissue (visible in dead fronds as brown dots). 2n = 20, 40, 42, 50, 60, 80. Flowering (rare) late spring--early fall. Mesotrophic to eutrophic, quiet waters in temperate to subtropical regions; 0--1000 m; Ala., Ark., Calif., Conn., Del., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Mass., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., S.C., Tenn., Tex., Va., Wash., W.Va., Wis.; Mexico; West Indies; Central America; South America. I know of no specimens of Wolffia brasiliensis from Rhode Island.
Thallus broadly ovoid, slightly asymmetrical, mostly 0.5-1.5 נ0.3- 1.0 mm, 1-1.5 times as long as wide, rounded at the tip, the upper side floating just above the water, punctate (post mortem) with brown pigment-cells, elevated near the middle into a conical papilla; 2n=20, 40, 50, 60, 80. Quiet water; N.J. and Md. to O., Ind., Mich., and Kans., s. to Fla., Tex., and S. Amer. (W. papulifera; W. punctata)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.