3. Wolffia columbiana H. Karst.
Pl.
98 h, i; Map 394
Fronds 0.5–1.4 mm long, lacking red or brown spots, the upper surface convex,
lacking papules, the tip rounded. 2n=30, 40, 42, 50, 70.
Scattered, mostly in the Ozark, Mississippi Lowlands, and Big Rivers Divisions
(U.S. and adjacent Canada, south to southeastern South America). Floating on
shallow, stagnant water of ponds, lakes, sloughs, ditches, and swamps,
sometimes forming mats; also in still backwaters of streams and rivers,
sometimes stranded on mud by receding waterline.