Egeria densa (leafy elodea)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Biology and Ecology
- Latitude/Altitude Ranges
- Natural enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Impact Summary
- Environmental Impact
- Impact: Biodiversity
- Social Impact
- Risk and Impact Factors
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Egeria densa Planch.
Preferred Common Name
- leafy elodea
Other Scientific Names
- Anacharis densa (Planch.) Vict.
- Elodea densa (Planch.) Casp.
- Philotria densa (Planch.) Small
International Common Names
- English: Brazilian elodea; Brazilian waterweed; common waterweed; dense waterweed; egeria
Local Common Names
- Brazil: elodes; erva dágua
- Cuba: egueria; elodea; elodea brasileña; elodea de Argentina
- Germany: Wasserpest, Dichtblättrige
- Japan: ookanadamo
- ELDDE (Egeria densa)
Summary of InvasivenessTop of page E. densa is highly desired in aquaria and small ponds, but has become a serious invasive species in larger bodies of fresh water, where dense mats reduce recreational options and crowd out native species as well as altering the hydrology. The principal means of entry is considered to be disposal of aquaria contents into local waterways, and spread is by vegetative means as many introduced populations comprise only male plants. Further introduction and spread is likely.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Monocotyledonae
- Order: Hydrocharitales
- Family: Hydrocharitaceae
- Genus: Egeria
- Species: Egeria densa
Notes on Taxonomy and NomenclatureTop of page The classification of this species as Egeria densa was established by Planchon in 1849 when he created the genus. Later, it was moved to the genus Elodea where it remained for a long time, and even today this binomial, Elodea densa, can be found in some publications. It is generally accepted at present that the original classification as part of the genus Egeria, shall be maintained.
DescriptionTop of page E. densa is a herbaceous, tender plant, with cauline leaves regularly disposed in close whorls, resembling cylinders 2-6 cm thick and 10-90 cm long. Stems sparsely branched, with short internodes, delicate, breaking easily with the parts forming new plants. In shallow water, plants can be anchored to the bottom, otherwise free-floating. Filament-like roots, at the base of plants and at some nodes, especially in broken pieces. Leaves sessile, lanceolate, 1-3 cm long and 5 mm large, apex rounded or acute, margins finely serrated, surface smooth, intensely green when receiving natural light, more pale in aquaria. E. densa normally presents four leaves per whorl, but can present five or six. Plants are dioecious. From the axils of some leaves arise spathes and from their interior emerge floral peduncles 2-6 cm long, that expose solitary flowers ca. 2 cm above the water surface. Male flowers are in groups of 2-4, from one spathe, the perianth formed by a calyx of 3 green sepals, corolas with 3 white petals, 10-15 mm long, stamens 9. Female flowers one per spathe, perianth like that of males, ovary unilocular formed by 3 carpels, androecium only residual with 3 yellow staminodes. Fruits are berry-like, ovate, 7-8 mm long and 3 mm wide with membranaceous and transparent pericarp. Seeds numerous, fusiform, 7-8 mm long, with a 2 mm filament present at the end.
Plant TypeTop of page Aquatic
DistributionTop of page E. densa is native to parts of Argentina, Brazil and Uruguay. Being one of the most common plants for aquaria, it has been widely distributed around the world. In many regions it has escaped and has become an invasive aquatic weed. Most reports come from Central and North America, Europe and Australasia.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Georgia (Republic of)||Present||EPPO, 2014|
|Indonesia||Present||Present based on regional distribution.|
|Nepal||Present||Rai and Pradhan, 2000|
|Mexico||Present||Introduced||Missouri Botanical Garden, 2003|
|USA||Present||Present based on regional distribution.|
|-Hawaii||Present||Introduced||Invasive||HEAR, 2002; USDA-NRCS, 2002|
|-Missouri||Present||Introduced||Invasive||Missouri Botanical Garden, 2003|
|-New Hampshire||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-New Jersey||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-New Mexico||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-New York||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-North Carolina||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-South Carolina||Present||Introduced||Invasive||USDA-NRCS, 2002|
Central America and Caribbean
|Costa Rica||Present||Introduced||Missouri Botanical Garden, 2003|
|Cuba||Present||Introduced||Invasive||Oviedo Prieto et al., 2012|
|Nicaragua||Present||Introduced||Missouri Botanical Garden, 2003|
|Puerto Rico||Present||Introduced||Invasive||USDA-NRCS, 2002|
|Argentina||Present||Native||Cabrera, 1968; USDA-ARS, 2003; EPPO, 2014|
|Bolivia||Present||Introduced||Missouri Botanical Garden, 2003|
|Brazil||Restricted distribution||Native||Not invasive||Kissmann, 1997; EPPO, 2014|
|-Bahia||Present||Oliveira et al., 2005|
|-Espirito Santo||Restricted distribution||Native||Not invasive|
|-Goias||Restricted distribution||Native||Not invasive|
|-Mato Grosso do Sul||Restricted distribution||Native||Not invasive|
|-Minas Gerais||Restricted distribution||Native||Not invasive|
|-Parana||Restricted distribution||Native||Not invasive|
|-Rio de Janeiro||Restricted distribution||Native||Not invasive|
|-Santa Catarina||Present||Native||Missouri Botanical Garden, 2003|
|-Sao Paulo||Restricted distribution||Native||Not invasive|
|Chile||Present||Lagos et al., 2008|
|Colombia||Present||Introduced||Missouri Botanical Garden, 2003|
|Paraguay||Present||Bini and Thomaz, 2005|
|France||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003; EPPO, 2014|
|Germany||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003; EPPO, 2014|
|Italy||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003; EPPO, 2014|
|Netherlands||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003; EPPO, 2014|
|Russian Federation||Present||EPPO, 2014|
|-Central Russia||Present||EPPO, 2014|
|-Russian Far East||Present||Kozhevnikova and Kozhevnikov, 2009|
|Spain||Restricted distribution||Pulgar and Izco, 2005; EPPO, 2014|
|Switzerland||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003; EPPO, 2014|
|UK||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003; EPPO, 2014|
|Australia||Present||Present based on regional distribution.|
|-New South Wales||Present||Introduced||Royal Botanic Gardens Sydney, 2003|
|-Tasmania||Present||Introduced||Royal Botanic Gardens Sydney, 2003|
|-Victoria||Present||Introduced||Royal Botanic Gardens Sydney, 2003|
|-Western Australia||Present||Introduced||Royal Botanic Gardens Sydney, 2003|
|Cook Islands||Present||Introduced||Invasive||HEAR, 2002|
|French Polynesia||Present||Introduced||Invasive||HEAR, 2002|
|New Zealand||Present||Introduced||Invasive||HEAR, 2002|
History of Introduction and SpreadTop of page Although E. densa has been widely distributed around the world as an aquarium plant, exact dates of introduction or naturalization in the wild are lacking. It was probably introduced into the USA in the early 1900s. It has only recently been discovered in Tahiti, French Polynesia (HEAR, 2002) indicating continuing spread. It is considered as possibly naturalized in South Africa and elsewhere in Africa though specific records are required.
Risk of IntroductionTop of page E. densa has been continually distributed, mainly by trade, for use in aquaria. When aquaria are cleaned, plants can enter water systems and so spread to lakes and other water bodies. Noting its continued and widespread use and availability, it is highly likely that this species will be further introduced, or where present, will become naturalized in local water systems. However, as its invasive character is becoming known, it is becoming regulated, notably in the USA and New Zealand, also recently in South Africa.
HabitatTop of page
E. densa is an aquatic plant, living submerged in fresh water, only its flowers being projected above the water surface. It is a weed in inland lakes and rivers, often shallow, mild or warm, in still or slow-moving water.
Habitat ListTop of page
|Freshwater||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page E. densa is an environmental weed not affecting cultivated crops to any extent, though may impact on agriculture by the blockage of irrigation channels.
Biology and EcologyTop of page Physiology and Phenology
E. densa is a plant with a great capacity of photosynthesizing when illuminated and releases great quantities of oxygen, which can be observed by small bubbles forming on the leaves. Therefore the plant is much used for physiology studies. It can form dense mats when present.
Plants can reproduce by seeds, but since the flowers are not hermaphrodite, the fertilization depends on transfer of pollen by certain insects. Thus the principal means of reproduction is vegetative, by fragmentation of stems. It appears that all E. densa in the USA and New Zealand is male and as such does not set seed, but has still shown itself as a highly invasive species solely through vegetative propagation.
Plants can only live immersed in fresh water, optimum temperatures of 15-17°C, tolerating a large range of pH. Enough light is required for photosynthetic activity and thus they cannot tolerate shaded water. Still water is prefered, or slow-running water.
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Natural enemiesTop of page
Means of Movement and DispersalTop of page E. densa is spread by moving waters which carry whole plants or stem fragments to new locations. It is also possible that animals may also unintentionally carry stem fragments. Plant parts can also become attached to boats which may disperse the plant. The principal cause of new introductions is, however, from the careless disposal of aquarium contents, including E. densa, into local watercourses.
Impact SummaryTop of page
|Fisheries / aquaculture||Negative|
ImpactTop of page Although there are positive economic impacts resulting in the trade in aquarium plants including E. densa, this is strongly countered by the costs of control as exercised in many areas where it has become a serious problem. Removal of E. densa from lakes and reservoirs in the USA costs some states several million dollars per annum.
Environmental ImpactTop of page When dense mats of E. densa have formed, native species are displaced, oxygen may be depleted and the character of stream and lakes may be changed. The effects on the environment may be substantial, affecting the hydrology also.
Impact: BiodiversityTop of page E. densa can out-compete and displace native vegetation, such as Elodea canadensis in the north-west USA.
Social ImpactTop of page Dense mats of E. densa will deleteriously affect recreational activities such as fishing, swimming or boating.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Highly mobile locally
- Has high reproductive potential
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Negatively impacts tourism
- Reduced amenity values
- Highly likely to be transported internationally deliberately
- Difficult/costly to control
UsesTop of page It is a well known and popular plant for use in aquaria and small ponds, not only for its attractiveness and resilience, but also for its oxygenating capacity which benefits the fish contained therein.
Similarities to Other Species/ConditionsTop of page Plants without flowers resemble species from the genera Elodea and Hydrilla. One distinction is on the whorls of leaves, most frequently Elodea with 3, Egeria with 4 and Hydrilla with 5 leaves, but this is not absolute.
Prevention and ControlTop of page
Mechanical removal such as cutting, hand pulling or netting is feasible for small infestations, though the ability to propagate from small stem fragments means that repeat clearing will be required, or even that infestations may spread if removal is not adequate. Use of the herbicide diquat has been recommended, although using chemicals in water bodies leads to evident environmental risks. The stocking with certain fish such as grass carp has been suggested, as E. densa is highly palatable, but there are no reports as to the effectiveness of this method.
ReferencesTop of page
Bini LM; Thomaz SM, 2005. Prediction of Egeria najas and Egeria densa occurrence in a large subtropical reservoir (Itaipu Reservoir, Brazil-Paraguay). Aquatic Botany, 83(3):227-238. http://www.sciencedirect.com/science/journal/03043770
Cabrera AL, 1968. Flora de la Provincia de Buenos Aires. II. Buenos Aires, Argentina: INTA, 309-404.
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
HEAR, 2002. Alien species in Hawaii. Hawaii Ecosystems at Risk, University of Hawaii, Honolulu, USA. http://www.hear.org/AlienSpeciesInHawaii/index.html.
Kissmann KG, 1997. Plantas Infestantes e Nocivas. Tomo 1, edition 2. Brazil: BASF, 256-258.
Lagos NA; Paolini P; Jaramillo E; Lovengreen C; Duarte C; Contreras H, 2008. Environmental processes, water quality degradation, and decline of waterbird populations in the Rio Cruces wetland, Chile. Wetlands, 28(4):938-950. http://www.bioone.org/doi/full/10.1672/07-119.1
Lorenzi H, 2000. Plantas daninhas do Brasil. Terrestres, Aquaticus, Parasitas e Toxicas, edition 2. Instituto Plantarum De Estudos Da Flora Ltda.
Missouri Botanical Garden, 2003. VAScular Tropicos database. St. Louis, USA: Missouri Botanical Garden. http://mobot.mobot.org/W3T/Search/vast.html.
Oliveira NMB; Sampaio EVSB; Pereira SMB; Moura Junior AM, 2005. Regeneration capacity of Egeria densa in reservoirs in Paulo Afonso, Bahia. (Capacidade de regeneração de Egeria densa nos reservatórios de Paulo Afonso, BA.) Planta Daninha, 23(2):363-369.
Oviedo Prieto R; Herrera Oliver P; Caluff MG, et al. , 2012. National list of invasive and potentially invasive plants in the Republic of Cuba - 2011. (Lista nacional de especies de plantas invasoras y potencialmente invasoras en la República de Cuba - 2011). Bissea: Boletín sobre Conservación de Plantas del Jardín Botánico Nacional de Cuba, 6(Special Issue 1):22-96.
Pulgar Í; Izco J, 2005. Egeria densa Planchon (Hydrocharitaceae) in Pontevedra province (Spain). (Egeria densa Planchon (Hydrocharitaceae) en la provincia de Pontevedra (España).) Acta Botanica Malacitana, 30:173-175.
Royal Botanic Garden Edinburgh, 2004. Flora Europaea Database. Royal Botanic Garden Edinburgh, UK. http://rbg-web2.rbge.org.uk/FE/fe.html.
Royal Botanic Gardens Sydney, 2003. Australia's Virtual Herbarium. Sydney, Australia: Royal Botanic Gardens. http://plantnet.rbgsyd.gov.au/cgi-bin/avh/avh.cgi.
USDA-ARS, 2003. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx
USDA-NRCS, 2002. The PLANTS Database, Version 3.5. National Plant Data Center, Baton Rouge, USA. http://plants.usda.gov.
Distribution MapsTop of page
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