Pontederiaceae, the Pickerelweed Family
Water hyacinth is an aquatic herb that is typically free-floating, but occasionally roots in mud when stranded. It grows as an annual in cooler climates, while in warm regions it is perennial. It is a rosette-forming plant, with a circular arrangement of leaves at about the same height and little or no stem developing between the roots and the leaves. Rosettes are interconnected by horizontal stems called stolons, forming dense mats that eventually cover the water surface. Submersed roots are usually bluish- to purplish-black in color and have a feathery texture. The petioles (leaf stalks) are usually bulbous or inflated, with a spongy interior. The leaf blades are coriaceous (leathery) and glabrous (hairless), broadly elliptic, ovate or orbicular in shape, with a glossy upper surface and numerous close-set parallel veins running lengthwise. The inflorescence is a bracteate spike that usually rises above the foliage, with four to 15 spirally arranged flowers, which open for only one day. Each flower has six lavender to blue (rarely pink or white) petals, which are fused into a tube basally. The uppermost petal is larger than the others and bears a darker spot with a yellow center. There are six stamens (three shorter than the others) with curved, glandular, hairy filaments. The fruit are three-celled, ovoid capsules to ½ inch long, each containing up to 300 tiny, longitudinally ribbed seeds.
Water hyacinth is native to the northern part of South America, including French Guiana, Guyana, Suriname, Venezuela and northeastern Brazil. It is widely naturalized in freshwater habitats throughout the subtropics and tropics, extending into warm temperate regions. In the United States, it has been reported from the Pacific states, Arizona and the Southeast, northward to Illinois and New Jersey.
This species has been vouchered with herbarium specimens from a majority of counties in Florida, including most of the central and southern peninsula and the eastern panhandle. It is found in a variety of still and slow-moving freshwater habitats, including ponds, lakes, streams, sloughs and canals.
Two other species of Eichhornia have been found in Florida. Eichhornia paniculata, commonly known as Brazilian water hyacinth, is native to Cuba, Jamaica and tropical America. It was reported from Manatee County in the early 20th century, but has not been collected recently. It is typically rooted in the mud and forms a larger plant with cordate leaves and flowers borne in a panicle. Eichhornia azurea, rooted or anchored water hyacinth, is also native to the Greater Antilles and tropical America, and is rarely found naturalized in Columbia County. As its common name suggests, plants are typically rooted rather than free-floating, and the sessile (lacking a petiole) leaves are alternately arranged on an elongated stem. Neither of these species have the inflated petiole characteristic of Eichhornia crassipes. Limnobium spongia, a native aquatic known as frogbit or American spongeplant, has vegetation that is superficially similar to water hyacinth, but its flowers are white, solitary and axillary, and it also lacks inflated petioles.
Water hyacinth flowers year-round in mild climates, with established mats of plants producing enormous quantities of seed, which can remain viable up to 20 years. Plants also reproduce readily from stolons. Growth rates are explosive, with mats doubling in size in a matter of weeks under favorable growing conditions. Plants are easily moved by both wind and water currents. Rosettes and stolons are also dispersed by boats and boat trailers.
Water hyacinth was introduced to the United States as an ornamental at the World’s Industrial and Cotton Exposition in New Orleans, Louisiana, in 1884-1885. A visitor to the exhibition brought the plant to Palatka, Florida, and planted it in an outdoor fish pond and around a boat dock on the St. Johns River. By 1896, it was reported to have covered a 200-mile stretch of the river. It was subsequently introduced to other Florida water basins when it was used as a cattle feed and as an organic mulch for citrus trees growing in sandy soils. It was estimated to have covered 126,000 acres of Florida’s public waters by the 1960s. At a cost of millions of dollars, various control techniques (including chemical herbicides, mechanical harvesting/chopping and biocontrol weevils and fish) have been employed in Florida, and populations have been reduced to more manageable levels.
The impacts of water hyacinth on water bodies are profound. Plants form dense mats that out-compete native aquatic plants. By reducing sunlight, oxygen levels and gas exchange at the water surface, this weed disrupts the ecology of water bodies, resulting in decreased diversity of phytoplankton, fish and other vertebrates. In addition to blocking navigational routes and irrigation channels, it can clog hydroelectric turbines, smother rice paddies, reduce fishing areas, restrict livestock access to water and impact recreational use of water bodies. Both Eichhornia crassipes and Eichhornia azurea are noxious weeds in Florida, and Eichhornia azurea is a federally prohibited aquatic plant.