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.
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
Found in isolated small colonies in permanent pools of stagnant water rich in organic matter. Known in Indiana only from Posey County. It has been found in only eight states.
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.