Introduced Species Summary Project
Water Hyacinth (Eichhorinia crassipies

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  water hyacinth
Common Name:  Water Hyacinth

Scientific Name:  Eichhorinia crassipes

Classification: Eichhorinia crassipes (Mart.) Solms

Phylum or Division: Magnoliophyta
Class: Liliopsida
Order: Liliades
Family: Pontederiaceae

Identification: Water hyacinth is a free-floating plant, which grows up to three feet in height. It has thick, waxy, rounded, glossy leaves, which rise well above the water surface on stalks. The leaves are broadly ovate to circular, 4 to 8 inches in diameter, with gently incurved sides, often undulate. Leaf veins are dense, numerous, fine and longitudinal. Water hyacinth leaf stalks are bulbous and spongy. Water hyacinth grows an erect thick stalk (to 20 inches long) at the top of which is a single spike of several (8 to 15) showy flowers. The flowers have 6 petals, purplish blue or lavender to pinkish, the upper petals with yellow, blue-bordered central splotches. Water hyacinth reproduces vegetatively by short runner stems (stolons) that radiate from the base of the plant to form daughter plants, and also reproduces by seed. Its roots are purplish black and feathery.

Original Distribution: The Water Hyacinth is native to the northern neotropics of South America.

Current Distribution: The Water Hyacinth is distributed currently through North America, South America, eastern Africa, and Asia.  

Site and Date of Introduction: 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.  It was introduced in Egypt in about 1879.  It spread to the Congo, the Nile and Lake Victoria in the 1950's.  It became introduced to Asia in 1888, and to Australia around 1890.

Mode(s) of Introduction: The Water Hyacinth was introduced from its native home in South America to various countries by well-meaning people as an ornamental plant.  

Reason(s) Why it has Become Established: 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. The seeds are dispersed by birds and can remain viable for 15-20 years. But the main method of reproduction is vegetatively, through stolons. A single plant under ideal conditions can produce 3,000 others in 50 days, and cover an area of 600 sq metres in a year.

Ecological Role: 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.

Benefit(s): 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.

The council of Scientific and Industrial Research has made varieties of high quality paper out of the stalk of the weed. The Agricultural University at Trivandrum, India, makes cattle feed out of the leaves and Ryan Foundation has taught villagers to crush the roots and make briquettes for their cook stoves. This weed must be commercialized and supplied to paper and board factories to save logging, deforestation and pollution.

Threat(s): Water Hyacinth grows profusely, forming dense mats that can spread across water surfaces eventually choking the entire water body. It can destroy native wetlands and waterway and kill native fish and other wildlife. Furthermore, it causes high evaporation rate and loss of water and degrades water quality. 

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. 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 Hyacinth impede transport of irrigation and drainage water in canals and ditches, hinder navigation, interfere with hydrolic schemes, decrease the possibilities for washing and bathing, decrease human food production, and decrease recreation.  Moreover, Water Hyacinth poses a health risk to humans and livestock because there is the risk that they might become entangled in the heavy growth and drown.

Control Level Diagnosis:  Highest Priority

Control Method:  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.

Control methods in other parts of the world involve Environmental Impact Assessments (EIA), mechanical removal operations, hebicide trial demonstrations, and increasing public awareness.


Photo Credits: ANS.html

Author: Myralyn Osei-Agyemang
Last Edited: November 22, 2002

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