Florida Prohibited Aquatic Plants List

Pistia stratiotes

Water lettuce

Introduction

Origin: Africa or South America1
Introduction to Florida: pre-1765 (accidental)2

Water lettuce is a floating plant. Experts disagree as to whether water lettuce is native to the U.S.: it has been present in Florida since as early as 1765 when the explorer, William Bartram, described and drew the plant in Lake George. This floating plant commonly forms large infestations which prevent boating, fishing and other uses of lakes and rivers. Water lettuce occurs in lakes, rivers and canals, occasionally forming large dense mats.

 

See more information about water lettuce as contained in the Langeland/Burks book, Identification & Biology of Non-Native Plants in Florida’s Natural Areas

View the herbarium specimen image from the University of Florida Herbarium Digital Imaging Projects.

For brief control information, see Efficacy of Herbicide Active Ingredients Against Aquatic Weeds by K. Langeland, M. Netherland, and W. Haller.

 

Description

As its name implies, water lettuce resembles a floating open head of lettuce. Water lettuce has very thick leaves. The leaves are light dull green, are hairy, and are ridged. There are no leaf stalks. Water lettuce roots are light-colored and feathery. Its flowers are inconspicuous. monocot, perennial free-floating except when stranded in the mud; singly or massed in large numbers; mother and daughter plants attached by short stolons thick soft leaves are formed in rosettes, with no leaf stems; leaves to 6 in. long; light green; with parallel ridges (veins), covered in short hairs; leaf margins wavy, top margins scalloped flowers inconspicuous (not observed in Florida till the 1980s though they had been flowering all along); nearly hidden in the center amongst the leaves; on small stalk, single female flower below and whorl of male flowers above roots hanging submersed beneath floating leaves; feathery, numerous fruit a green berry

Impacts

 

  • Pistia stratiotes mats clog waterways, making boating, fishing and almost all other water activities, impossible
  • water lettuce mats degrade water quality by blocking the air-water interface and greatly reducing oxygen levels in the water, eliminating underwater animals such as fish
  • water lettuce mats greatly reduce biological diversity: mats eliminate native submersed plants by blocking sunlight, alter emersed plant communities by pushing away and crushing them, and also alter animal communities by blocking access to the water and/or eliminating plants the animals depend on for shelter and nesting
  • in Florida, water lettuce has never been the problem that water hyacinth has been; water lettuce is essentially under “maintenance control” in Florida