Botanical name: Spirodela polyrrhiza
Common name: Spirodela, Duckweed
Part used in Chinese medicine: whole plant
Major Chinese medicine actions:
Releases exterior, induces sweating, clears and drains heat,
vents rashes, alleviates itching, promotes urination, reduces swelling
Photo Credits: (top to bottom)
Photo 1: Duckweeds Wolffia globosa and Sprodella polyrrhiza; 09/2005;
author Eric Guinther; permission under GFDL
Spirodela polyrrhiza, also called Giant Duckweed, is actually a tiny aquatic plant and is only “giant” in relation to other varieties of duckweed. It does not have actual leaves and stems but the plant body (thallus) expands to about 8 mm, or less than 1/3 inch wide, and functions as a leaf. The thallus is a glossy green color on the top, has a reddish purple lower surface, and a cluster of thin roots hanging down into the water.
The plant is found growing alone or in clusters of 2-5. Multiplying in colonies, these clusters of duckweed often look like a mat of green pumpkin seeds floating on the surface of the water. It is shown in the photo above growing with a larger leafed aquatic plant.
The plant grows in still or very slow moving water such as in lakes, ponds, marshes and slow streams, in areas that are sheltered from wind. It provides a high protein food source for waterfowl and some fish. In Africa and Asia is has been harvested for cattle and pig feed.
Growing and Propagation
The plant requires full sun and grows in water that is rich in nitrates and lime. It rarely flowers and when it does, they are tiny, occurring in a pouch containing two male flowers and one female flower. In the autumn, the small buds sink to the bottom of the pond or lake, remaining there during the winter months. In this way they can even survive when the surface of the pond freezes.
In spring, these buds rise to the surface and germinate. Giant Duckweed grows very rapidly, especially if the water is warm and nutrient rich, and it can form extensive floating mats. It self propagates easily without assistance.
Harvesting and Preparation
The plant should be washed and cleaned thoroughly, and then dried. Good quality Fu Ping has a green upper surface and purplish lower surface, with long rootlets.