Duckweed

Lemnoideae is a subfamily of flowering aquatic plants known as duckweeds, water lentils or water lenses, which float on the surface of still or slow-moving fresh water and wetlands. They are structurally simple, lacking an obvious stem or leaves, with bodies formed from a small thallus or frond only a few cells thick, often holding air pockets for flotation, and depending on species may have no roots or simple rootlets. Duckweeds mostly reproduce asexually by budding, though they occasionally produce tiny flowers with stamens and pistils; the genus Wolffia produces the smallest known flower, just 0.3 millimeters long.