water lettuce USDA PLANTS SYMBOL: PIST2
Pistia stratiotes L.
Synonym(s): tropical duckweed

Appearance
Pistia stratiotes is a sprawling, semi-woody shrub that invades wetlands in Florida. The green stems are up to 15 ft. (4.6 m) long and prickly.
Foliage
Leaves are flashy and arranged in a rosette. They measure 0.75-6 in. (2-15 cm) in length. The leaves are green to grayish-green, and have dense white hairs and parallel veins on their surface. As its common name indicates, the plant resembles a floating head of lettuce.
Flowers
This plant flowers year-round in southern Florida, but peaks during summer and early autumn.
Fruit
The hydrosoil under a Pistia stratiotes infestation was shown to hold 4,196 seeds/m2. Mature seeds in fruits had an 84% germination rate.
Ecological Threat
Pistia stratiotes, forms extensive mats that can block navigational channels, impede water flow in irrigation and flood control canals, and disrupt submersed animal and plant communities (Sculthorpe, 1967; Attionu, 1976; Bruner, 1982; Sharma, 1984). Pistia stratiotes is among the world’s worst weeds (Holm et al., 1977). It has been placed on prohibited plant lists in Florida (FDEP, 2000), Louisiana (LDWF, 2000), Mississippi (MDAC, 1997), and Texas (TPWD, 2000), and is considered a noxious species (an invasive species of concern, but not regulated) in South Carolina (SCDNR, 2000) and Delaware (DDFW, 2000).

Identification, Biology, Control and Management Resources