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Pistia, or Pistia stratiotes, also known as water lettuce or water cabbage, is a perennial aquatic plant most native to tropical areas. Pistia has thick, rigid, green leaves that are shaped like an open rosette, similar to an open head of lettuce, while the roots of the plant resemble light feathers. Pistias reproduce through seeds or by creating shoots with daughter plants.
To thrive, pistia needs a wet habitat such as a lake or river, and will sometimes grow in more muddy environments. Pistias can survive in most temperate climates, although they thrive in tropical environments. These plants will not tolerate extreme cold but will bounce back from minor freezes. Pistias can live in temperatures ranging from 59°F to 95°F (15°C to 35°C), yet optimal temperature is closer to between 72°F and 86°F (22°C to 30°C).
Pistias can be found all over the world, which makes it difficult to identify its origins with certainty. Some scientists believe pistia is a plant native to the United States, while others believe it is an exotic species. The plant is mentioned in explorer William Bartram's writings, dating from 1765; he notes seeing pistia plants while in what is now Florida. Some scientists believe the plants arrived in the ballasts of explorers' ships and are, perhaps, originally from South America or Africa.
The plants can grow into thick mats over bodies of water, becoming a nuisance. When this happens, water activities such as boating, fishing and swimming are nearly impossible. An overabundance of pistia plants can also affect an ecosystem by blocking all sunlight below the water, disrupting plant and animal life below the surface. It will also reduce the amount of oxygen in the water, threatening fish and other aquatic animals. On the surface of the water, a mat of pistia plants will push away and choke off other water plants that may be a source of food or habitat for aquatic wildlife.
In some areas where overgrowth must be controlled, mechanical harvesters are used to chop up and remove pistias from bodies of water. Biological controls are also used, mostly in the form of the water leaf weevil. Weevils are introduced to an environment with an overabundance of pistias, and the beetles and beetle larvae feed on the plants, destroying them.
The pistia is a popular plant for personal use. It may be used in aquariums or in outdoor decorative ponds. It can be purchased from aquarium supply stores or through plant nurseries that supply water plants.