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Water
Hyacinth Eichhornia crassipes Keladi Bunting (Malay) Water Hyacinths are the only large aquatic herb that can float on the water unattached to the bottom. They float on bloated air-filled hollow leaf stalks which give them their Malay name that means "pregnant tuber". Their roots trail underwater in a dense mat. The Water Hyacinth has special adaptations to allow it to grow and spread rapidly in freshwater. They can withstand extremes of nutrient supply, pH level, temperature, and even grow in toxic water. They grow best in still or slow-moving water. |
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The Water Hyacinth was introduced from its native home in South America to various countries by well-meaning people as an ornamental plant; to the US in the 1880's; to Africa in the 1950's spreading to the Congo, the Nile and Lake Victoria; also in India.
The fast-growing Water Hyacinth soon becomes a noxious weed outside its native habitat. Plants interlock in such a dense mass that a person could walk on a floating mat of them from one bank of a river to the other. The presence of Water Hyacinth disrupts all life on the water. They clog waterways preventing river travel, block irrigation canals, destroy rice fields, ruin fishing grounds. By shading the water, these plants deprived native aquatic plants of sunlight and animals of oxygenated water. As the mats decay, there is a sharp increase in nutrient levels in the water, which spark off algal growths that further reduces oxygen levels.
Water Hyacinths are difficult (if not impossible) to destroy. In the US, arsenic was used on a large scale which only partially cleared the weeds but poisoned the ecosystem. Fire and explosives were also attempted, but the plants reproduce rapidly even from the tiniest fragment and simply grew back. The most effective measures are biological controls, hundreds of which have been studied for this purpose. Two weevils, a moth and two types of fungi have been introduced to successfully control the plant. Other creatures that keep the plant in check include fish (Chinese grass carp (Ctenopharyngo idella) and Tilapia melanopleura and T. mossambica) and manatees.
Uses: In Singapore, as elsewhere, it was cultivated as pig food, but have become a serious nuisance in reservoirs. There are studies on using the plant to detoxify sewage and sludge.
Role in the habitat: In their native habitat of the Amazon, Water Hyacinths provide food for their natural predators which voraciously keep the plant in check. The annual flooding of the Amazon also flush out huge quantities to sea each year.
LINKS
- University of Florida Centre for Aquatic and Invasive Plants: lots of details about the devastating effect of the introduction of the plant.
- The Nature Conservancy Wildland invasive species program: Lots of details about their spread and control.
- Non-native freshwater plants on the Washington State Dept of Ecology website: fact sheet.
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- Ivan Polunin, "Plants and Flowers of Singapore", Times Editions, 1987 (p. 68: description, habitat, distribution, photo).
- Prof S. Talalaj, "The Strangest Plants in the World", Hill of Content, 1991 (p. 122-124: description, history, distribution, photo).
- Tony Whitten and Jane Whitten (ed.), "Indonesian Heritage: Plants", Making the Most out of Weeds by Mohamad Soerjani, Editions Didier Millet, 1996 (p. 126: description).
- Dr E Soepadmo (ed.), "The Encyclopaedia of Malaysia: Plants", Aquatic Flowering Plants by Cheksum Supiah Tawan, Editions Didier Millet, 1998 (p. 72-73: habit)
- Science Club, River Valley High School, "A Guide to the Flora and Fauna of Schools in Singapore", Hillview Publications, 1991 (p. 66: description, habits, habitat, photo).