Duckweed, the Green Pond Phenom

—Mary Gillick, Program Director

Spirodela polyrhiza, or common duckweed. Image: Christian Fischer on commons.wikimedia.org

If you pass by Nanderwhere Pond this summer at the Rye Nature Center, you may do a double take and think you are looking at a lawn where the pond once was.

This floating green carpet is composed of tiny plants called Spirodela polyrhiza commonly known as duckweed. This vascular plant has roots that dangle an inch or so into the water column and pull nutrients and water out for their leaf-like stems to carry out photosynthesis.

The plant thrives in still ponds or slow-moving wetlands and by its huge numbers indicates when the water is overloaded with nutrients. The source of these extra minerals is probably over-fertilized lawns bordering the property.

Duckweed reproduces quickly by vegetative means or buds that originate from the stem of the original plants. It can initially populate a pond when ducks or other waterfowl carry the tiny plants in on their feet.

As summer progresses the duckweed converts much of its extra biomass to starch which weighs them down and forces the plants to fall to the pond mud. During winter the plants continue to metabolize and use up some of that stored food so that by spring the plants float back up to the pond surface.