Duckweed, water lens, or bayroot, are freshwater aquatic plants. They float in still or slow-moving fresh water and wetlands. There are five genera, with a total of 33 to 38 species.
These plants are very simple: They lack an obvious stem or leaves. Most of each plant is a small organized "thallus" or "frond" structure only a few cells thick. Often it has air pockets and floats on or under the water surface. Some have no root and some have one or more simple rootlets.
Reproduction is usually by asexual budding. Occasionally, three tiny flowers are produced for sexual reproduction. These flowers have two stamens and a pistil. From this occasional reproduction is produced a seed in an air bag that floats. The flower of the duckweed genus Wolffia is the smallest known, just 0.3 mm long.