Pistia stratiotes L.
Water lettuce is a free floating plant that is capable of forming dense mats on the surfaces of lakes, ponds, rivers and other bodies of water. Water lettuce is found throughout the warmer coastal regions of the United States from Florida to California, and is very sensitive to cold temperatures. Water lettuce has thick leaves that are light green and rigid, closely resembling a head of lettuce. The reproductive mechanism of water lettuce is the seed, which are concealed within the fruit of the plant until maturity at which time they are spread by water.
Water lettuce has an uncertain origin. Water lettuce was first identified in Australia in 1946/47, although it is now known to occur throughout the warmer regions of the world.