El Salvador’s Lake Suchitlan is overwhelmed by invasive water lettuce which is impacting thousands of families dependent on fishing and tourism.

About Water Lettuce
Water lettuce (Pistia stratiotes), also known as water cabbage or Nile cabbage, is a free-floating, tropical and subtropical aquatic plant with velvety, light green leaves arranged in a rosette that resembles a head of lettuce. It is widely used in water gardens and aquariums for its aesthetic appeal and ability to absorb excess nutrients, but it is considered an invasive species in many regions due to its rapid growth rate. 

Key Characteristics

• Appearance: The leaves are thick, ridged, and covered in short, white, water-repellent hairs, which help the plant float. The leaves form a cup-like rosette and can grow up to 6 inches wide and 10 inches long.
• Roots: Long, feathery, unbranched roots dangle beneath the floating leaves, providing habitat for small aquatic organisms and fish fry.
• Flowers and Fruit: It produces small, inconspicuous white or green flowers in the center of the rosette, followed by small green berries that contain seeds.
• Reproduction: Water lettuce primarily reproduces asexually through stolons (runners) that produce "daughter" plants, forming dense, interconnected mats. It can also reproduce by seed, which can overwinter in the mud in some climates. 

Habitat and Growing Conditions

• Habitat: It thrives in still or slow-moving freshwater bodies like ponds, lakes, marshes, and irrigation channels.
• Climate: It prefers warm water temperatures (70-80°F or 21-30°C) and is sensitive to frost. In colder climates, it is typically grown as an annual or overwintered indoors.
• Light: Grows well in full sun to partial shade.          
• Water Quality: Prefers a neutral to slightly acidic pH (6.5-7.5) and can help purify water by absorbing excess nutrients like nitrogen and phosphorus, which inhibits algae growth. 

Uses and Concerns

• Benefits: In contained environments, water lettuce provides shade, which helps cool the water and reduces algae blooms. Its roots offer shelter for fish and other aquatic life. It has also been studied for its potential in phytoremediation (cleaning contaminated water) and has traditional medicinal uses in some cultures.
• Invasiveness: Outside of its native pantropical range, it is often a highly invasive weed. Dense mats can:
  • Block sunlight, killing submerged native plants.
  • Deplete dissolved oxygen levels, harming fish and other aquatic animals.
  • Impede water flow in canals and hinder recreational activities like boating and fishing.
  • Serve as a breeding ground for mosquitoes, including those that are vectors for diseases.

• Toxicity: The plant contains calcium oxalate crystals and is considered toxic to dogs and not palatable for human consumption in large quantities, though it has been used as a famine food or animal feed in some areas. 

Due to its potential to become invasive, many regions and states (such as Florida, Louisiana, and Texas) have listed it as a prohibited or noxious plant, and it should not be released into natural waterways. 

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