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| NAS - Nonindigenous Aquatic Species |
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Common Name: Brazilian waterweed
Synonyms and Other Names: Anacharis densa (Planch.) Victorin, Elodea densa (Planch.) Caspary, Philotria densa (Planch.) Small & St. John
Taxonomy: available through 
Identification: Egeria densa is a dioecious, submersed perennial found in lentic and lotic freshwater systems. Only male plants are found in the U.S. and, even in its native range, male plants outnumber female plants by as much as 6:1 (Cook and Urmi-König 1984).
Leaves and stems are generally are a bright green and the short internodes length yeild a very leafy appearance. Leaves which are are minutely serrated (needing magnification) and linear, are 1-3 cm long, up to 5mm broad, and found in whorls of four to eight. The lowest leaves may be opposite or in whorls of 3; middle and upper leaves are in whorls of 4 to 8. Stems are erect, cylindrical, simple or branched, and grow until they reach the surface of the water where they form dense mats. Flowers have three petals which are white (18-25 mm) and float on or rise just above the water's surface on slender peduncle. Slender roots are unbranched and typically a white to pale color. Adventitious roots are freely produced from double nodes on the stem (The Washington State Department of Ecology, 2003).
Native Range:
South America (Brazil, Argentina, Uruguay)
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 Alaska |
Hawaii |
Caribbean |
Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences: Egeria densa has invaded New Zealand (Coffey and Clayton 1986), Japan (Haramoto and Ikusima 1988, Hamabata and Kobayashi, 2002), Chile (Cook and Urmi-König 1984) and Australia (Roberts et al. 1999) and numerous areas across Europe (Dutartre et al. 1999, .
In the US, E. densa has invaded lakes and ponds across most East Coast states, from New England (Vermont, New Hampshire, Massachusetts, Connecitcut) south to Florida; west through the Gulf Coast states of Alabama, Mississippi, Louisiana, and Texas and in scattered locations of Arkansas, Missouri, Oklahoma, Kansas, Nebraska, Colorado, New Mexico, Utah, Arizona. Considered established in Hawaii, though not recorded as spreading in recent years. In the Western US, it has heavily infested areas of the California delta as well as many lakes in Oregon and Washington. Most recently (2007 & 2008) three waterbodies near Moscow and Boise, Idaho were found and treated for infestations.
Means of Introduction: Introduced world-wide through the aquarium trade - sold widely as good "oxygenator" plant and dispersed secondarily by boat trailers and vegetative dispersal downstream.
Status:
Impact of Introduction: Dense stands of E. densa may restrict water movement, trap sediment, and cause fluctuations in water quality. Severe infestations may impair recreational uses of a water body including navigation, fishing, swimming, and water skiing. In Brazil , E. densa (as well as E. najas, Ceratophyllum demersum, and Eichhornia crassipes) have severely infested hydropower reservoirs. It was estimated that 48,000 cubic meters of aquatic weeds were removed from water intake structures in Jupia Reservoir (Marcondes et al. 2000).
Remarks:
References
Coffey, B.T. and J.S. Clayton. 1986. Submerged macrophytes of Lake
Pupuke , Takapuna , New Zealand . New Zealand Journal of Marine and
Freshwater Research 21: 193-198.
Cook, C.D.K. and K. Urmi-König. 1984. A revision of the genus E. densa (Hydrocharitaceae). Aquatic Botany 19: 73-96.
Dutartre, A., J. Haury, and A. Jigorel. 1999. Succession of Egeria densa in a drinking water reservoir in Morbihan (France). Hydrobiologia 415: 243-247.
Hamabata,
E., and Y. Kobayashi. 2002. Present status of submerged macrophyte
growth in Lake Biwa: Recent recovery following a summer decline in the
water level. Lakes & Reservoirs: Research and Management 7: 331-338.
Haramoto, T. and I. Ikusima. 1988. Life cycle of E. densa Planch., an aquatic plant naturalized in Japan . Aquatic Botany 30: 389-403.
Marcondes,
D. A. S., A. L. Mustafa, R. H. Tanaka, D. Martins, E. D. Velini, and R.
A. Pitelli. 2000. Studies for aquatic plant management in hydro
electrical lakes in Brazil. Abstract. Annual Meeting of the Aquatic
Plant Management Society. San Diego, CA .
Roberts, D.E., A.G. Church, and S.P. Cummins. 1999. Invasion of E. densa into the Hawkesbury-Nepean River, Australia. Journal of Aquatic Plant Management 37: 31-34.
Other Resources:
Author: V. Howard Morgan
Revision Date: 3/3/2009 Citation for this information:
V. Howard Morgan. 2010. Egeria densa. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1107> Revision Date: 3/3/2009
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