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Small But Mighty Duckweed Is Common on Our Waterways

There is something green covering our waterways, but what can it be? Is it mold, algae, scum? Look closely. Can you see a leaf? It’s duckweed!

A frog in water coated with duckweed.
A frog in water coated with duckweed. (Photo courtesy of Penny Schnay)

There are 38 unique species of duckweed, and nine are found in the United States. Some species might have distinct shapes, making it easy to recognize them. Other types are so similar you would need to magnify them to notice the differences. Common duckweed is the most popular species. It is found throughout North America and on other continents as well.

Looking at duckweed, you may think you are seeing a single tiny leaf floating on the water with a single tiny root hanging into the water. Technically, the leaf-like part is called a thallus. It acts very much like a leaf because it contains chlorophyll, so it can make its own food. The thallus also traps tiny air bubbles that allow it to float.

Common duckweed is also known as Lemna minor. It is a very fitting scientific name. Lemna is the Greek word for a water plant, and minor means small. The plants in the duckweed family have the smallest flower known on our planet. It is only 1 millimeter when in full bloom. That’s the same size at the point on a sharpened pencil. Once pollinated, a 1-millimeter-sized fruit is formed that contains one tiny seed.

This little flower rarely blooms, but duckweed has other ways of reproducing. Each plant can make clones of itself. A clone is an exact copy of the original. For duckweed, the clone is often called an offset. As it is growing, it is connected to the mother plant by a thin stem called a stipe. The stipe will wither away, and the clone becomes independent. Almost as soon as the young offset is unattached, it is ready to produce its own offset. Common duckweed is so effective at reproducing this way, its numbers can double in less than a day.


Words to know

Algae: A simple, nonflowering aquatic plant.

Chlorophyll: Green pigment in plants responsible for absorption of light to provide energy for photosynthesis.

Nuisance: A person, thing or circumstance that causes inconvenience or annoyance.

Starch: An odorless, tasteless substance found in plant tissues that functions as a carbohydrate store.

Wastewater: Water that has been used in a home, business or as part of an industrial process.


In the fall, when the weather gets colder and the days get shorter, common duckweed is ready to change gears to prepare for winter. Then, instead off creating offsets, a small starchy bud called a turion is formed. This turion sinks to the bottom and waits until winter is over. When the weather warms up, this turion is ready to spring into action. It uses the starchy part to get energy and then creates a tiny bubble of gas. This allows it to float to the surface, where it can grow into the tiny plant.

Duckweed is an important part of watery habitats in many ways. It is eaten by ducks, turtles, fish and insects. Some dragonfly and damselfly species will lay their eggs on the floating plant. It is also useful as camouflage for both predator and prey — predators sneakily waiting to ambush unsuspecting prey, and prey hoping to remain hidden from stalking predators.

Duckweed plants out of water.
Duckweed. (Photo via Shutterstock)

Duckweed is often considered a weed and a nuisance because it reproduces so rapidly. It can quickly take over the surface of a small pond. But this rapid growth can also be a benefit. Common duckweed is used in bioremediation. That is a fancy word meaning it can remove pollution from water. It is used to clean wastewater, and scientists keep researching other ways the plant can be useful.

If you walk along the shore of a pond or river and see a blanket of green, take a moment to investigate. Chances are, it is the tiny but mighty common duckweed.


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