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.
Aquatic herb Flowers: occurring rarely, borne one per plant body, lacking sepals and petals, with one stamen and one nearly smooth seed. Fruit: bladder-like (utricle) and thin-walled. Roots: absent. Plant body: not differentiated into stem and leaves, solitary or in pairs, green with scattered pigment cells visible under 10x magnification, 0.5 - 1.6 mm long, one to one and a half times as deep as wide, one-third to two-thirds times as deep as wide, elliptical with a rounded tip and a tent-shaped projection at the center, always floating (even when crowded), lacking air spaces in tissue. A conical cavity at the tip produces daughter plants, while a cavity beside the midvein of the upper surface produces flowers.
Similar species: Wolffia columbiana is distinguished by having a spherical plant body that is deeper than wide and lacks pigment cells. The plant body of Wolffia borealis differs by having a pointed, upward-turned tip and lacking a tent-shaped projection in the center.
Flowering: early September
Habitat and ecology: Quiet waters of ponds, ditches, and streams. This species is likely more common than records show.
Occurence in the Chicago region: native
Notes: The genus Wolffia consists of the world's smallest flowering plants.
Etymology: Wolffia is named after J.F. Wolff, German botanist and physician (1778-1806). Brasiliensis means Brazilian.
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.