Greater Duckweed Spirodela polyrhiza

Greater Duckweed is a perennial aquatic plant found in slow-moving or still waters of ponds, bogs, lakes, and swamps all over the world.  Nitrogen and other nutrients will be common to these waters.  Protection from wind and waves is crucial to the plants survival. 

Growing on the water surface, this simple, oval-shaped life form consists of a single, flat thallus, which is a plant that combines the functions of both the leaf and the stem.  Each tiny (.35" x .27") thallus is filled with even smaller pockets of air that give it floating capabilities.  

The upper side of the thallus is a medium green, while the underside is typically a reddish-purple.  A single, red node is located on the upper side.  Each node can have 5-12 veins that curve inward.  These are not visible to the naked eye.

Although rare to bloom, flowers are produced from 2 pouches on the thallus.  One pouch will contain a single female flower with a single pistil, the other will contain 2 male flowers that contain a single stamen.  The female flower is replaced by a tiny fruit in the form of a sack which has 1 to 2 seeds.  In lieu of flowering, the thallus can produce buds that are attached to the mother plant for a period of time before separating into individual plants.  

Its roots are a group of tiny rootlets coming from a node on the underside of the thallus.  

Winter and cooler weather cause the thallus to form a starchy off-set called a winter turion.  Bud-like in form, and brown to olive green, the turion will detach from the mother plant and sink to the bottom of the water.  As spring approaches, it will rise to the surface.  

While this plant is a food source for some aquatic mammals such as ducks and turtles, it also provides a habitat for aquatic organisms.  Due to its metabolically active cells and little structure fibers, its tissue has two times the protein, fat, nitrogen and phosphorus plants, giving the plant a high nutritional value.

Insects, Diseases, and Other Plant Problems:  Its rapid growth can cause this plant to spread agressively.  It also spreads by mammals such as beavers and muskrats that spread this plant from one wetland to another when the sticky roots attach to their wet fur.