Duckweed is a free-floating aquatic plant that grows in both still and running freshwater, such as lakes, rivers, and streams. Contrary to what one might expect from the name, no ducks are involved in the growth habits of the plant, although ducks undoubtedly feed on it when they find it growing. Depending on the circumstances, duckweed can be an extremely invasive species, or a welcomed aquatic plant. Native plant societies usually have specific information about its status in a particular area, for people who are curious.
Any plant in the genus Lemna can be considered a duckweed. They usually have small vestigial roots, if they have roots at all, and they grow in the form of thick green carpets of rounded free-floating thalloids, flattened structures which resemble leaves. Duckweed can rapidly spread to cover a waterway, resisting all attempts to eliminate it. These plants typically reproduce by budding, although they can produce small flowers on occasion, and it prefers water which is rich in nitrogen and other nutrients.
In some cases, duckweed can be a boon. The plant readily filters substances, including toxins, out of the water, and some biologists use it in phytoremediation. It can also provide shelter for aquatic animals, in addition to nutrition for larger creatures like ducks and geese. Some species are even considered attractive, making them potentially appealing as ornamentals in the garden. Some scientists have even genetically engineered duckweed to perform specific functions.
This plant can quickly turn into a major problem, especially in areas where water is polluted with excessive nutrients, such as fertilizer runoff from farms, or spills from manure pits at confined animal feeding operations (CAFOs). Well-nourished duckweed can spread rapidly across a body of water, choking out native plant species and threatening resident fish. The plant can also clog propellers and filtration systems, making it a nuisance to humans as well as animals.
If duckweed suddenly appears in an area where it has not been present before, this can be a sign that something about the environment has changed. Droughts, nutrient pollution, and unusual weather patterns can all create blooms, and a proliferation of the plant should be regarded as a cause for concern until the cause has been identified. Some gardeners like to use duckweed as an ornamental for their water features, but they should think carefully before doing this, as it can get out of control or spread to local bodies of water.