Ber. Geobot. Inst. ETH Stiftung Rubel 44:137. 1977.
Fronds boat-shaped, 0.7–1.5 mm, 1.3–2 times as long as wide, 0.7–1 times as deep as wide, with point at apex bent upward; papilla absent; upper surface intensely green, with 50–100 stomates; pigment cells present in vegetative tissue (visible in dead fronds as brown dots). 2n = 20, 22, 30, 40.
Phenology: Flowering (very rare) summer–early fall.
Habitat: Mesotrophic to eutrophic, quiet waters in temperate regions
Elevation: 0–1400 m
Alta., B.C., Ont., Que., Calif., Colo., Idaho, Ill., Ind., Iowa, Kans., Ky., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.Y., Ohio, Okla., Oreg., Pa., S.Dak., Tenn., Utah, Vt., Wash., Wis.
The name Wolffia punctata has been applied to this species in error.
I know of no specimens of Wolffia borealis from Rhode Island.