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The World Conservation Union calls common water hyacinth (Eichhornia crassipes) one of the worst weeds in the world. A floating aquatic plant, water hyacinth grows rapidly, causing extensive ecological and economic damage in water systems. The plant displaces other species, obstructs waterways, blocks water intake pipes, and interferes with fishing. Dense populations of the species damage fish spawning grounds, increase water evaporation rates, and deposit a great deal of organic matter in a system. When this organic matter decomposes, the oxygen level in the water is lowered, and fish populations suffer.
Water hyacinth grows in slow-moving or still water. Under ideal conditions, it doubles its mass every two weeks. The species survives a variety of environmental conditions. It tolerates a wide range of pH and temperatures, both fresh and brackish water, and fluctuations in water levels. It also survives some toxic substances. The plant has spikes of eight to 15 flowers and round, shiny leaves. Each flower has six purple to lavender petals, the uppermost of which has a bright yellow spot. Leaves are four to eight inches in length. Thick, upright stalks lift both the flowers and the leaves above the water surface. When the wind catches these upright leaves, plants are dispersed throughout the water body. Roots are four to 118 inches (10-300 centimeters) in length, make up about half of the mass of the plants, and contain compounds that may prevent predation from insects. The plant produces stolons, or short stems that develop into new plants. Stolons are the most common form of reproduction; seed production also occurs. Seeds maintain their viability for up to 20 years.
A native of Brazil, water hyacinth now thrives in most tropical and subtropical regions of the world. Because of its showy flowers, the plant was intentionally moved around the world for its ornamental qualities. It is believed to have been introduced to the United States in 1884 at an exhibition in Louisiana. It arrived in Africa in 1879, in Asia in 1888, and in Australia in 1890.
Water hyacinth populations have been managed with herbicides, hand pulling, mechanical harvesting and biological control. Hand pulling works for small infestations, but is too labor-intensive to control larger populations. Herbicides, including copper sulfate, 2,4-D, and glyphosate, reduce populations of water hyacinth but damage other organisms in the ecosystem. Several of water hyacinth’s natural enemies, including insects and fungi, have been used to control populations with varying degrees of success. Five of these biocontrol agents are used in the United States: Two weevils, a moth and two types of fungi. Attempts to use explosives and fire to keep populations in check have not been successful.
Some populations of water hyacinth have been successfully controlled. In the 1950s, water hyacinth occupied 126,000 acres of Florida’s waterways. A combination of herbicides, harvesting, and biocontrol methods reduced Florida’s water hyacinth population to 2,000 acres.
Although the harm caused by the species generally outweighs its benefits, a few uses have been found for water hyacinth. It has been fed to pigs, used to remove toxins from sewage, and made into paper. One study in Bangladesh found arsenic in water can be removed by water hyacinth, producing safer drinking water.
- Michael Batcher, Element Stewardship Abstract for Eichhornia crassipes (Martius) Solms (The Nature Conservancy, 2000);
- Columbia University, “Introduced Species Summary Project: Water Hyacinth (Eichhorinia crassipes),” www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/invbio_home.html;
- Mir Misbahuddin and Atm Fariduddin, “Water Hyacinth Removes Arsenic from Arseniccontaminated Drinking Water,” Archives of Environmental Health (November-December 2002);
- World Conservation Union, “Eichhornia crassipes (Aquatic Plant),” www.issg.org.