They are tiny, have only one root and are considered either a very useful plant or a pest in waterways around the world. They are the Lemnaceae, a family of plants called duckweeds. They are the smallest flowering plants known and most have only two leaves. These little angiosperms are mighty versatile, though; they may hold the answers to everything from nutrition for a growing global population to the age-old challenge of de-salinization. All this and they're invasive, too.
Duckweed grows fruit and produces seed, but its real talent is vegetative reproduction. In a lake, pond or gently moving river with agricultural fertilizer runoff or sanitary sewer effluent, duckweed reproduces at exponential rate, according to W.P. Armstrong of Palomar College. According to Armstrong, each plant produces up to a dozen plants during its lifetime of 30 to 60 days, depending on variety.
Duckweed's Bad Rap
Population explosions of duckweed, called "blooms," can cover freshwater ponds and marshes in a matter of a few days or weeks, giving it the reputation of an invasive nuisance. But it blooms fastest in polluted or stagnant waters. A duckweed bloom can actually be beneficial because the shade it creates prohibits the growth of algae that often consumes oxygen.
Duckweed is an undemanding and productive food crop. It tolerates lower temperatures than many crops, an acidic pH as low as 5 and grows fastest in stagnant or polluted waters. Its nutritive value and compact form makes it a natural choice for fish farming in the Far East. The World Bank agriculture division reports that some varieties grown under ideal conditions yield 5 to 15 percent of their weight in fiber and 35 to 45 percent protein. Duckweed provides high concentrations of trace minerals, beta carotene and xanthophylls, all valuable for animal feed.
The reason that duckweed contains all those terrific nutrients is in great part due to the fact that it gobbles pollutants out of the water. The little plant soaks up excessive amounts of nitrogen, phosphates and potassium out of detergents, ammonia and wastewater. They thrive on the nitrates produced by waste products of fish and other animal denizens of the watershed. The uses of duckweed for bioremediation extend to using it in wastewater treatment; experimentation is ongoing in the western U.S., Europe and hot-climate countries.
Duckweed may have the potential to further clean water. Wastewater may even be re-claimed for agricultural use after treatment with duckweed. The U.S. Environmental Protection Agency is investigating the use of duckweed in drawing the components of DDT out of the soil in a photosynthetic process called phytotransformation. The U.N. Food and Agriculture Organization have found that duckweed will even soak up sodium, suggesting that it may be useful for desalinization research.