Duckweed
Lemna sp.

This primitive plant consists of a flat, leaf-like thallus (or frond) floating freely on the water surface with one or more roots hanging from it. Each thallus is about a quarter of an inch long, while the roots are about an inch long. The roots are completely free and do not act as anchors (see photograph). Usually, many fronds carpet the surface of still or slow-moving water. The plant's tiny white flower is rare and hard to see. Duckweed can reproduce vegetatively. In winter it will sink below the ice; it also withstands being out of water for considerable periods and this helps it to be spread by traveling birds and other animals.

Duckweed is often considered a nuisance because it covers waterways. However, it is a food source for many animals including beaver, muskrat, and many duck species. It also provides good camouflage for frogs, and their eggs stick to the fronds allowing them to float nearer the surface where conditions are better for development.

Duckweed is also a good indicator of water quality since it is not found if the pH is above 8 or if the water contains industrial pollutants such as heavy metals. It will, however, filter out nitrogen and phosphorous from water which is contaminated with fertilizer run-off.

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