florida Early Detection Network


Brazilian water-weed


Egeria densa Planch.


Frog's Bit family


Egeria densa









Synonyms: Anacharis densa (Planch.) Vict., Elodea densa (Planch.) Casp.


Botanical Glossary

Egeria densa is a submersed, freshwater, perennial herb whose stems are usually 0.3-0.6 m (1-2 ft.) long, though they can be longer (up to 20 ft.). It is usually rooted in the substrate. The stems are cylindrical and simple or branched. The leaves and stems are bright green in color. The leaves are usually around 2 cm (0.8 in.) long and arranged in whorls of 4-6 leaves. The leaf margins have fine teeth that can be seen with the aid of a hand lens (10x). The flowers have three white petals that are approximately 2 cm (0.75 in.) across and are situated about 2.5 cm (1 in.) above the water. These flowers, if present, can be seen from the summer to the fall. Page References Crow & Hellquist 28, Flora of North America 32, Gleason & Cronquist 636, Holmgren 606, Magee & Ahles 130. See reference section below for full citations.


Elodea canadensis Michx., Elodea nuttallii (Planch.) St. John, Hydrilla verticillata (L.f.) Royle


Egeria densa reproduces vegetatively from plant fragments. These fragments are dispersed by water birds and by attaching to boats. Fragments or entire plants can also come from disposed aquariums and water gardens.


Egeria densa is native to the central Minas Geraes region of Brazil. It is also native to the coastal areas of Argentina and Uruguay. This plant has invaded several countries in Europe, Asia, Australia, New Zealand and Chile. In the United States the plant is present in the Pacific Northwest, California, Utah, Illinois, Nebraska, Kansas, Texas, the Southeast and in the East from New England to Florida. It is not yet present in Maine or Rhode Island.


The first record of this plant outside of cultivation is from 1893 in Millneck, Long Island. It was offered for sale in the U.S. in 1915. (The first European record is in 1910 in a canal in Leipzig, Germany). It first appeared in Massachusetts around 1940 in Abington. The first official record of Egeria densa in Connecticut was in 1992 from Westport. Egeria densa was a popular aquarium plant because it was a good "oxygenator." It was likely transmitted into natural areas via people pouring their aquaria into nearby lakes.


Aquatic,Lake or Pond,River or Stream, Egeria densa can be found in both still and flowing water. These include lakes, ponds, small streams and ditches. In the Northeast it is usually found in small ponds.


Egeria densa forms dense monotypic stands that crowd out native aquatic plants. It also provides a very poor habitat for fish. It reproduces easily via plant fragments. This plant also interferes with fishing, boating, swimming, and other recreational activities. It is considered a noxious weed in some states.


Washington State Department of Ecology

California Invasive Plant Council


Documentation required: Herbarium specimen or mounted snippet of the whole plant. Best time for documentation: Spring, summer, fall.


Integrated Taxonomic Information System - Has general taxonomic information about the species.

The PLANTS Database - General information including a map

University of Florida - Center for Aquatic and Invasive Plants - General information and photographs

University of Maine Cooperative Extension


Barreto, R. R. Charudattan, A. Pomella, and R. Hanada. 2000. Biological control of neotropical aquatic weeds with fungi. Crop Protection 19(8-10):697-703.

Chambers, P.A., J.W. Barko and C.S. Smith. 1993. Evaluation of invasions and declines of submersed aquatic macrophytes. Journal of Aquatic Plant Management 31:218-220.

Collier, K.J., P.D. Champion and G.F. Croker. 1999. Patch- and reach- scale dynamics of a macrophyte-invertebrate system in a New Zealand lowland stream. Hydrobiologia 392(2):89-97.

Crow, G.E. and C.B. Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America. Vol #2. University of Wisconsin Press, Madison.

De Winton, M.D., and J.S. Clayton. 1996. The impact of invasive submerged weed species on seed banks in lake sediments. Aquatic Botany 53(1-2):31-45.

Duggan, I.C., J.D. Green, K. Thompson, and R.J. Shiel. 2001. The influence of macrophytes on the spatial distribution of littoral rotifers. Freshwater Biology 46(6):777-786.

Dutartre, A., J. Haury and A. Jigorel. 1999. Succession of Egeria densa in a drinking water reservoir in Morbihan (France). Hydrobiologia 415:243-247.

Dutartre, A., J. Haury, A. Jigorel. 1999. Succession of Egeria densa in a drinking water reservoir in Morbihan (France). Hydrobiologia 415: 243-247.

Feijoo, C.S. Momo,F.R., Bonetto, C.A. and Tur, N.M. 1996. Factors influencing biomass and nutrient content of the submersed macrophyte Egeria densa Planch. in a pampasic stream. Hydrobiologia 341: 21-26.

Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. Volume #1. Oxford University Press.

Flora of North America Association ed. 2000. Flora of North America vol. 22. Oxford University Press, Oxford, New York.

Gantes, H.P., and A.S. Caro. 2001. Environmental heterogeneity and spatial distribution of macrophytes in plain streams. Aquatic Botany 70(3):225-236.

Gleason, H.A. and A.C. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed. New York Botanical Garden, Bronx, New York.

Haramoto, T. and I. Ikusima. 1988. Life cycle of Egeria densa Planch., an aquatic plant naturalized in Japan. Aquatic Botany 30: 389-403.

Holmgren, N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual. New York Botanical Garden, Bronx, New York.

Howard, W.C., A.M. Schwarz and V. Reid. 1996. Patterns of aquatic weed regrowth following mechanical harvesting in New Zealand hydro-lakes. Hydrobiologia 340(1-3):229-234.

Les, D.H. and L.J. Mehrhoff. 1999. Introduction of nonindigenous aquatic vascular plants in southern New England: a historical perspective. Biological Invasions 1:281-300.

Leyi, N., and J. Pokorny. 1999. Effects of cutting on the growth and photosynthesis of Egeria densa (Planchon) caspary. Acta Hydrobiologica Sinica 23:187-192.

Magee, D.W and H.E. Ahles. 1999. Flora of the Northeast. University of Massachusetts Press, Amherst.

National Agricultural Library of the U.S. Department of Agriculture. Species Profiles. //www.invasivespecies.gov.

Wells, R.D.S., M.D. De Winton, and J.S. Clayton. 1997. Successive macrophyte invasions within the submerged flora of Lake Tarawera, Central North Island, New Zealand. New Zealand Journal of Marine and Freshwater Research 31(4):449-459.

Wilcock, R.J., P.D. Champion, J.W. Nagels, and G.F. Croker. 1999. The influence of aquatic macrophytes on the hydraulic and physio-chmical properties of a New Zealand lowland stream. Hydrobiologia 416:203-214.

USDA, NRCS. 2001. The PLANTS Database, Version 3.1. (//plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.