Water hyacinth (Eichhornia crassipes) is a floating freshwater plant that is native to South America. It has spread around the tropical and subtropical world where it clogs up shipping lanes and prevents native plants from getting sunlight, choking them out by rapidly reproducing and forming dense mats of vegetation.
Water hyacinth primarily reproduces by division. Runners just under the surface of the water send out shoots which form new rosettes of leaves and break off, floating away to form a new colony. This is so efficient that water hyacinth can double its population in six days; it is one of the fastest growing plants in the world.
Water hyacinth produces clusters of berries, each with up to 450 seeds. Tropical-grown plants produce more seeds per berry than subtropical-grown plants. These usually sprout when the water level is low and mud is exposed for them to germinate and root in. The seeds can survive 15 years when dry or when under water.
Water hyacinth is difficult to control and must be removed manually, often with large skimmers or specialized rakes. It can then be dried and used as compost or biomass for biofuels. Another method is to tow it out to sea and let the saltwater kill it. Several states including Arizona, Florida and South Carolina have placed restrictions on its sale or cultivation.