The lovely lavender flowers with the distinctive yellow spot may be attractive to look at, but water hyacinth is one of the most aggressive invasive plant species in the United States.
The water hyacinth is native to South America, and was introduced to North America near the end of the nineteenth century as an ornamental plant, i.e. because it looked pretty. Little did the importers realize what a monster they were unleashing.
The plant grows vigorously, and can double its volume in about two weeks. It can completely cover lakes and rivers, preventing boat traffic and crowding out other species. Its rapid growth can deprive waterways of oxygen and block sunlight. Fish have trouble swimming through the dense root structure. Water hyacinth is on the federal noxious weeds list and is illegal to own or transport in most southern states.
In Florida, it grew unchecked for decades, choking off thousands of acres of waterways. It also provided an ideal habitat for mosquito growth. Florida water management crews spent years removing the accumulated growths using herbicides and mechanical methods. They now check waterways for new growth and control it as soon as it’s found.
In the seventies, the USDA began releasing certain weevils and a moth that are natural predators of the hyacinth, and this effort has met with some success. In 2000, the USDA published information about new biological controls that were identified in Ecuador, where water hyacinth populations are kept in check by natural enemies. This year, the USDA has released news about yet another insect, a planthopper, which they hope will help control the spread of water hyacinth.
The plant is typically free-floating. It has large round or oval leaves that are dark green with a waxy, waterproof texture, and are about six inches across. They grow on long spongy stalks that help the plant to stay afloat, and a mass of dark thin roots hangs underneath, growing down about two feet. The flowers grow on a single spike containing about fifteen blooms.
Reproduction can occur through runners or seeds. The runners can form daughter plants and expand the aquatic area covered, forming a solid mat of plant material that can weigh tons. One acre of water hyacinth weighs over 200 tons. A single plant can produce thousands of seeds. If the seeds are eaten and dispersed by wildlife, the plants can spread even farther. Ungerminated seeds can be viable for years.
Water hyacinth is not cold tolerant, and is sometimes used for ornamental ponds in summer in cold climates, where it is expected to die out during the winter. However, if the dead plants are not disposed of properly, they can make their way into lakes and rivers and re-establish themselves during warmer temperatures. They can grow in most freshwater environments.
Its scientific name is eichhornia crassipes: “eichhornia” refers to a Prussian cultural minister, Johann Albrecht Eichhorn, whose name was given to the plant as an homage by botanist Karl Kunth; and “crassipes” means thick, referring to the thick stalks.
The water hyacinth does have some good qualities. Pond owners find that it filters and cleans cloudy pond water and helps to control algae blooms, but it can easily take over if it’s not carefully controlled. If you use it, only plant it in enclosed environments and never dispose of plant waste or cuttings in natural waterways. Check with your state agricultural service to be sure it is legal in your location.
