Sunday, October 16, 2011

long green blades of wild

long green blades of wild
water iris crisscross
above a small round pond

I found these wild water iris growing in the water along the shore of a lake in Wisconsin and brought a few rhizomes home to plant in and around the edge of our small round pond. The "yellow flags" with their pinwheel beacons bloom in late spring. The shape of the blossom of the original European native water iris, pseudacorus, was the model for the French fleur-de-lis. After the flowers die, the tall leaf blades create an attractive display all summer. In autumn the leaves begin to turn yellow and fall across the pond, interlinking like a Scottish rapper sword dance. 

          Unbeknownst to me, the iris carried with them some tiny hitchhikers, called duckweed. These aquatic plants are the world’s smallest and simplest flowering plants, having neither leaves nor stems but only a flat frond that floats on the surface of the water with a single root dangling underneath. Common duckweed, lemna, reproduces by budding. They multiplied so quickly on our small pond that they soon covered the entire surface, blocking sunlight and possibly upsetting the pond's oxygen balance. Fish eat duckweed, which helps control its spread, and fish farmers use it for feeding fish. However, it can become a nuisance and various methods are used to control it it. Mechanical skimmers usually don't completely eradicate it, whereas herbicides do, but chemicals in a water source can be dangerous. We don't have fish but we do have frogs, and both the tadpoles and the adult frogs love the cover that duckweed provides. The dense shade prevents algae from growing in the pond, which is a major problem in our neighbor's big pond. Duckweed also removes nitrates, so environmentalists use it as a biological water purifier. Not surprisingly, ducks love to eat duckweed, and it is also a popular food for humans living in Southeast Asia. Higher in protein than soybeans, it is an inexpensive food source for fish, fowl and humans. It just goes to show that one person's pest is another person's protein.

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