FULL SCIENTIFIC NAME
Pistia stratiotes L.
FAMILY NAME COMMON
FAMILY SCIENTIFIC NAME
Pistia stratiotes is a free-floating aquatic with feathery roots that can reach up to 50 cm (19.7 in.) in length. The fleshy leaves of this plant are arranged in a rosette and measure 2-15 cm (0.75-6 in.) 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. Pistia stratiotes flowers in the late summer, but the flowers plant are small and inconspicuous. The male and female flowers are arranged in an inflorescence type known as a spadix, with 6-8 male flowers in a single whorl around the center and one female flower below. The spathe, a bract-like leaf surrounding the spadix, is white to pale green, glabrous on the inside and pubescent on the outside. The fruits of this plant are light green berries that contain light brown seeds that are cylindrical in shape and measure 1 mm (0.04 in.). Page References Bailey 180, Magee & Ahles 306. See reference section below for full citations.
Pistia stratiotes reproduces primarily vegetatively by means of daughter plants attached to stolons. The daughter plants have the potential to break off from the parent plant and be moved via water currents or boats to start new populations. It can also reproduce sexually via seeds.
The nativity of this plant is not known. It was reported as being in Florida in 1765 by William Bartram. However, it could also be native to South America or Africa. In the United States this plant is mainly found in the southeast from Florida west to Texas. There have been outlying populations reported from as far west as California and Hawaii and as far north as New York and New Jersey, which are assumed to be introductions.
HISTORY OF INTRODUCTION IN NEW ENGLAND
This plant has not yet been reported as naturalized from New England, but has been reported in neighboring New York. It was reported early on from Florida (in 1765), which could indicate that it is native there. However, it could also have been brought via ship ballast by the early colonizers of this country. In New England it is often introduced intentionally into ponds and streams for decorative purposes. Since this plant is sensitive to frost, it dies back in the winter and is often reintroduced each year.
HABITATS IN NEW ENGLAND
Aquatic, Lake or Pond, Roadside, Yard or Garden. Pistia stratiotes is most often found in slow-moving or still water, such as lakes, ponds and reservoirs. It is also often found in water gardens and aquaria.
Pistia stratiotes has the ability to crowd out native aquatic plants, as well as to make infested water bodies inhospitable to different animals. For example, the coverage of plants on the water surface can reduce the oxygen available for fish in the water below. It also impedes recreational activities such as boating and swimming. Since this plant can spread vegetatively, it has the potential to spread via boats and water currents. It is sold in the aquarium and water garden trade, which could be a threat if the plants are not disposed of carefully. There is concern that with repeated introductions the plant could become less sensitive to frost, and eventually be able to sustain persistant populations in New England.
Documentation required: Photograph of plant. Best time for documentation: Summer, early fall
Integrated Taxonomic Information System - Has general taxonomic information about the species.
The PLANTS Database - General information including a map
Pacific Island Ecosystems at Risk (PIER) - Information about the threat of this species
USGS Nonindigenous Aquatic Plant Distribution Information - Map with records of this plant in the United States
Invasive.org - Additional images of water lettuce
Agami, M. and K.R. Reddy. 1990. Competition for between Eichornia crassipes (Mart.) Solms and Pistia stratiotes L. cultured in nutrient-enriched water. Aquatic Botany 38:195-208.
Bailey, L. H. 1949. Manual of Cultivated Plants. Macmillan, New York.
Chadwick, M.J. and M. Obeid. 1966. A Comparative study of the growth of Eichornia crassipes Solms and Pistia stratiotes L. in water-culture. Journal of Ecology 64: 563-575.
Cilliers C.J., D. Zeller, G. Strydom. 1996. Short- and long-term control of water lettuce (Pistia stratiotes) on seasonal water bodies and on a river system in the Kruger National Park, South Africa. Hydrobiologia 340(1-3): 173-179.
den Hollander N.G., I.W. Schenk, S. Diouf and M.J. Kropff, A.H. Pieterse. 1999. Survival strategy of Pistia stratiotes L. in the Djoudj National Park in Senegal. Hydrobiologia 415: 21-27.
Dewald, L.B. and L.P. Lounibos. 1990. Seasonal growth of Pistia stratiotes L. in south Florida. Aquatic Botany 36:263-275.
Dray, F.A. and T.D. Center. 1988. Seed production by Pistia stratiotes L. (water lettuce) in the United States. Aquatic Botany 33:155-160.
Flora of North America Association ed. 2000. Flora of North America vol. 22. Oxford University Press, UK.
Holm, L.G., D.L. Plunckett, J.V. Pancho and J.P. Herberger. 1997. World's worst weeds. University of Hawaii Press, Honolulu.
Langeland K.A., O.N. Hill, T.J. Koschnick and W.T. Haller. 2002. Evaluation of a new formulation of Reward Landscape and Aquatic Herbicide for control of duckweed, waterhyacinth, waterlettuce, and hydrilla. Journal of Aquatic Plant Management 40: 51-53.
Lemon G.D. and U. Posluszny. 2000. Shoot development and evolution in Pistia stratiotes (Araceae). International Journal of Plant Sciences 161(5): 721-732.
Magee, D.W and H.E. Ahles. 1999. Flora of the Northeast. University of Massachusetts Press, Amherst.
USDA, NRCS. 2001. The PLANTS Database, Version 3.1. (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.