Plant 114

Eichhornia crassipes (Mart.) Solms (Pontederiaceae)


Water hyacinth

The water hyacinth is a freshwater, floating aquatic herb. Originally from the Amazon Basin, it is an aggressive species that has become widely naturalised in many tropical and sub-tropical climates around the world.

The shape of the glossy, bright, green leaves vary according to whether they are submerged or held clear of the water. The inflated leaf petioles act as buoyancy aids and the leaf blade apparently performs the function of a sail. The plant has thick stems of spongy parenchyma tissue, which help it to stay afloat. The roots do not usually form any sort of anchor, allowing the plant to float and move freely.

The flowers are a beautiful violet-lavender colour with a central yellow blotch on the banner petal. They are held on a spike above the water and foliage and open in the morning, usually lasting for a day. Bees pollinate the flowers and after pollination the inflorescence curves downwards allowing the fruits to mature below the water surface. It produces masses of seed that remain viable for a long time.

Where water hyacinth has established as a weed, the most common reason for its occurrence is because it has been introduced as an ornamental plant. Eichhornia crassipes has a rapid vegetative reproductive cycle. In a year a single plant is capable of producing a huge, impenetrable floating mat of several hundred square metres. Given optimum conditions for growth, a single plant can give rise to 1,200 offspring in just four months.

As an introduced species it disrupts the function of native ecosystems. The density of the vegetation on the water surface reduces the available sunlight and lowers the levels of oxygen in the water. It also creates a good breeding environment for mosquitoes.

If left unchecked Eichhornia crassipes can cause severe disruption to fishing, water traffic and shipping, irrigation and crop yields. Glyphosate is used as a chemical control. Water hyacinth can also be removed from waterways manually and the use of biological controls has had some success. Water hyacinth control is problematic because it is an aquatic plant and so prolific. One of the best methods of control is to educate the public and reduce its introduction.

In Bangladesh harvested plants are dried and used to feed livestock. Elsewhere the leaves are used to make widely available household items such as baskets, mats and furniture. Manatees graze on water hyacinth in its native habitat.

Further reading

Huxley A 1992. Dictionary of gardening. The Royal Horticultural Society.

Global invasive species database 2006. Eichhornia crassipes.

Kate Pritchard