Duckweed

No doubt many of you are noticing a covering of green floating stuff on quiet water of marshes and streams around the state. Some of that may be algae, but a closer look at much of it reveals many plants that are small floating oval structures about an eighth of an inch or so across. When I was a kid I thought they were baby water lilies. Some people know this plant as duckweed. Botanists know the plant as Lemna turionifera.

Duckweed is one of the smallest flowering plants on earth, although it seldom flowers. It can be found in still water habitats where it prefers slightly alkaline conditions. Duckweed does best in the cool temperatures of spring and fall and can spread quickly by budding to form a dense covering over the water. When fall comes around the plants will form small perennating structures called turions which will sink to the bottom of the body of water and overwinter in a dormant state. The following spring they will rise to the surface and form the plant we so frequently see.

What looks like a floating leaf in duckweed is not actually a true leaf. It is more accurately described as a flattened, oval, frond or thallus. Descending below the thallus is one small root.

Until recently the duckweeds were placed in their own family the Lemnacea or duckweed family. Recent DNA studies conducted the family, however, have resulted in their placement in the arum family or Araceae. So duckweed is now placed in the same plant family as philodendron, peace lily, and Jack-in-the-pulpit.

Duckweed is nutritious and high in protein. It is an important food item for ducks as well as other water birds and some fish. It is even used to feed livestock in some parts of the world such as Asia, Africa, and India and surprisingly is even eaten by humans in some parts of Asia.

Perhaps even more interesting is the use of this plant bioremediation to clean water. Duckweed absorbs large amounts of nutrients from the water, particularly nitrogen and potassium. As a result, duckweed it is now being used in the treatment of municipal wastewater. The city of Devils Lake, for example, uses duckweed to treat their wastewater. Located just west of Devils Lake on highway 19, this is the second largest facility of its kind in the world and the only one in North Dakota. Not only can the duckweed clean the wastewater, but it can also be harvested and used to feed livestock or as compost.

So the next time you see some duckweed, give some thought to the biology, ecology and utility of this small and interesting plant. It really has a lot going for it.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.