If you've visited the pond at Prairie Ridge, you have likely noticed the carpet of bright green that covers some to most of the surface of the water. That green isn't the work of algae, as you might expect. Instead, you're seeing one of the world's smallest flowering plants, Giant Duckweed (Spirodela polyrhiza).
Giant Duckweed is a tiny, free-floating aquatic plant that is typically found in ponds, lakes, and along the shore of slowly flowing streams. The "leaves" (though they're not true leaves) are bright green on top and purple-red on bottom and float on the surface of the water with the reddish roots dangling down into the water. The species in our pond, Spirodela polyrhiza, has two or more roots attached to each plant that are important for absorbing nutrients from the water.
Duckweed flowers infrequently and usually spreads by budding. Buds develop at the edge or base of the fronds and eventually drift off to form new plants. The plants can thus spread very easily and become extremely abundant on the surface of the water. When Duckweed does flower, it produces three tiny flowers that consist only of two stamens and a pistil. Little is known about how the flowers form or exactly how they work, however.
Duckweed is important to a wide variety of organisms that live in the habitats where it occurs. It is especially important as habitat for aquatic insects that use its foliage to hide or as a food source, though some surface-dwelling species stand on top of it. Duckweed is also a nutritious food for waterfowl (especially ducks, as the name suggests) and attracts many animals that feed on aquatic insects, such as fish.
Under the right conditions, Duckweed can become a weedy pest, covering the entire surface of the water and interfering with essential processes underwater. It can spread easily from one body of water to the next as well, so it can become invasive. However, it has also been intentionally introduced in some areas due to its great ability to absorb pollutants and salt from freshwater systems. Because it buds and reproduces so quickly and is low in fiber but high in nutrients, Duckweed is also sometimes used as a supplemental food for fish, livestock, and humans and has been considered as a source of plant material for producing biofuels.
The Duckweed is still visible at Prairie Ridge as we near winter. When you visit, be sure to take a close look at the Duckweed on the pond. You never know what you'll find lurking amongst its leaves!
Find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive .