Waterlettuce (Pistia stratiotes) is an invasive plant. It is a native of South America.
This is a floating perennial with fleshy leaves forming a basal rosette that, as the common name alludes, resemble a head of lettuce. Dense populations of P. stratiotes can clog waterways, making fishing, swimming and boating difficult. Thick colonies of water-lettuce block the air-water interface which reduces the amount of dissolved oxygen in the water making it less suitable habitat for fish species. These dense mats can also block animal access to the water and may crowd or shade out native plants upon which other organisms depend for food or shelter. .