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Datasheet

Egeria densa (leafy elodea)

Summary

  • Last modified
  • 03 January 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Egeria densa
  • Preferred Common Name
  • leafy elodea
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Monocotyledonae
  • Summary of Invasiveness
  • 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 princip...

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Pictures

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PictureTitleCaptionCopyright
Habit showing dense mat of submerged foliage.
TitleHabit
CaptionHabit showing dense mat of submerged foliage.
CopyrightSheldon Navie
Habit showing dense mat of submerged foliage.
HabitHabit showing dense mat of submerged foliage.Sheldon Navie
Habit showing dense mat of submerged foliage.
TitleHabit
CaptionHabit showing dense mat of submerged foliage.
CopyrightSheldon Navie
Habit showing dense mat of submerged foliage.
HabitHabit showing dense mat of submerged foliage.Sheldon Navie
Flowers and leaves.
TitleFlowers
CaptionFlowers and leaves.
CopyrightSheldon Navie
Flowers and leaves.
FlowersFlowers and leaves.Sheldon Navie
Close-up of flower.
TitleFlower
CaptionClose-up of flower.
CopyrightSheldon Navie
Close-up of flower.
FlowerClose-up of flower.Sheldon Navie

Identity

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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

EPPO code

  • ELDDE (Egeria densa)

Summary of Invasiveness

Top 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 Tree

Top 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 Nomenclature

Top 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.

Description

Top 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 Type

Top of page Aquatic
Perennial
Seed propagated
Succulent
Vegetatively propagated

Distribution

Top 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 Table

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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/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

Georgia (Republic of)PresentEPPO, 2014
IndonesiaPresentPresent based on regional distribution.
-SumatraPresentVeldkamp, 2008
NepalPresentRai and Pradhan, 2000
TurkeyPresentEPPO, 2014

North America

MexicoPresentIntroducedMissouri Botanical Garden, 2003
USAPresentPresent based on regional distribution.
-AlabamaPresentIntroduced Invasive USDA-NRCS, 2002
-ArizonaPresentIntroduced Invasive USDA-NRCS, 2002
-ArkansasPresentIntroduced Invasive USDA-NRCS, 2002
-CaliforniaPresentIntroduced Invasive USDA-NRCS, 2002
-ConnecticutPresentIntroduced Invasive USDA-NRCS, 2002
-DelawarePresentIntroduced Invasive USDA-NRCS, 2002
-FloridaPresentIntroduced Invasive USDA-NRCS, 2002
-GeorgiaPresentIntroduced Invasive USDA-NRCS, 2002
-HawaiiPresentIntroduced Invasive HEAR, 2002; USDA-NRCS, 2002
-IllinoisPresentIntroduced Invasive USDA-NRCS, 2002
-KansasPresentIntroduced Invasive USDA-NRCS, 2002
-KentuckyPresentIntroduced Invasive USDA-NRCS, 2002
-LouisianaPresentIntroduced Invasive USDA-NRCS, 2002
-MarylandPresentIntroduced Invasive USDA-NRCS, 2002
-MassachusettsPresentIntroduced Invasive USDA-NRCS, 2002
-MississippiPresentIntroduced Invasive USDA-NRCS, 2002
-MissouriPresentIntroduced Invasive Missouri Botanical Garden, 2003
-NebraskaPresentIntroduced Invasive USDA-NRCS, 2002
-New HampshirePresentIntroduced Invasive USDA-NRCS, 2002
-New JerseyPresentIntroduced Invasive USDA-NRCS, 2002
-New MexicoPresentIntroduced Invasive USDA-NRCS, 2002
-New YorkPresentIntroduced Invasive USDA-NRCS, 2002
-North CarolinaPresentIntroduced Invasive USDA-NRCS, 2002
-OklahomaPresentIntroduced Invasive USDA-NRCS, 2002
-OregonPresentIntroduced Invasive USDA-NRCS, 2002
-PennsylvaniaPresentIntroduced Invasive USDA-NRCS, 2002
-South CarolinaPresentIntroduced Invasive USDA-NRCS, 2002
-TennesseePresentIntroduced Invasive USDA-NRCS, 2002
-TexasPresentIntroduced Invasive USDA-NRCS, 2002
-UtahPresentIntroduced Invasive USDA-NRCS, 2002
-VermontPresentIntroduced Invasive USDA-NRCS, 2002
-VirginiaPresentIntroduced Invasive USDA-NRCS, 2002
-WashingtonPresentIntroduced Invasive USDA-NRCS, 2002

Central America and Caribbean

Costa RicaPresentIntroducedMissouri Botanical Garden, 2003
CubaPresentIntroduced Invasive Oviedo Prieto et al., 2012
NicaraguaPresentIntroducedMissouri Botanical Garden, 2003
Puerto RicoPresentIntroduced Invasive USDA-NRCS, 2002

South America

ArgentinaPresentNativeCabrera, 1968; USDA-ARS, 2003; EPPO, 2014
BoliviaPresentIntroducedMissouri Botanical Garden, 2003
BrazilRestricted distributionNative Not invasive Kissmann, 1997; EPPO, 2014
-BahiaPresentOliveira et al., 2005
-Espirito SantoRestricted distributionNative Not invasive
-GoiasRestricted distributionNative Not invasive
-Mato Grosso do SulRestricted distributionNative Not invasive
-Minas GeraisRestricted distributionNative Not invasive
-ParanaRestricted distributionNative Not invasive
-Rio de JaneiroRestricted distributionNative Not invasive
-Santa CatarinaPresentNativeMissouri Botanical Garden, 2003
-Sao PauloRestricted distributionNative Not invasive
ChilePresentLagos et al., 2008
ColombiaPresentIntroducedMissouri Botanical Garden, 2003
ParaguayPresentBini and Thomaz, 2005
UruguayPresentNativeUSDA-ARS, 2003

Europe

BelgiumPresentEPPO, 2014
FrancePresentIntroduced Invasive Royal Botanic Garden Edinburgh, 2003; EPPO, 2014
GermanyPresentIntroduced Invasive Royal Botanic Garden Edinburgh, 2003; EPPO, 2014
HungaryPresentEPPO, 2014
ItalyPresentIntroduced Invasive Royal Botanic Garden Edinburgh, 2003; EPPO, 2014
NetherlandsPresentIntroduced Invasive Royal Botanic Garden Edinburgh, 2003; EPPO, 2014
Russian FederationPresentEPPO, 2014
-Central RussiaPresentEPPO, 2014
-Russian Far EastPresentKozhevnikova and Kozhevnikov, 2009
SpainRestricted distributionPulgar and Izco, 2005; EPPO, 2014
SwitzerlandPresentIntroduced Invasive Royal Botanic Garden Edinburgh, 2003; EPPO, 2014
UKPresentIntroduced Invasive Royal Botanic Garden Edinburgh, 2003; EPPO, 2014

Oceania

AustraliaPresentPresent based on regional distribution.
-New South WalesPresentIntroducedRoyal Botanic Gardens Sydney, 2003
-TasmaniaPresentIntroducedRoyal Botanic Gardens Sydney, 2003
-VictoriaPresentIntroducedRoyal Botanic Gardens Sydney, 2003
-Western AustraliaPresentIntroducedRoyal Botanic Gardens Sydney, 2003
Cook IslandsPresentIntroduced Invasive HEAR, 2002
French PolynesiaPresentIntroduced Invasive HEAR, 2002
New ZealandPresentIntroduced Invasive HEAR, 2002

History of Introduction and Spread

Top 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 Introduction

Top 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.

Habitat

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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 List

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CategoryHabitatPresenceStatus
Freshwater
Freshwater Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top 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 Ecology

Top 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.

Reproductive Biology

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.

Environmental Requirements

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 Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
0 2175

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Ctenopharyngodon idella Herbivore New Zealand
Oreochromis zillii Herbivore

Means of Movement and Dispersal

Top 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.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Soil, sand and gravelWater Yes

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) None
Crop production None
Environment (generally) Negative
Fisheries / aquaculture Negative
Forestry production None
Human health None
Livestock production None
Native fauna None
Native flora None
Rare/protected species None
Tourism Negative
Trade/international relations None
Transport/travel Negative

Impact

Top 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 Impact

Top 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: Biodiversity

Top of page E. densa can out-compete and displace native vegetation, such as Elodea canadensis in the north-west USA.

Social Impact

Top of page Dense mats of E. densa will deleteriously affect recreational activities such as fishing, swimming or boating.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Highly mobile locally
  • Has high reproductive potential
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts tourism
  • Reduced amenity values
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately
  • Difficult/costly to control

Uses

Top 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/Conditions

Top 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 Control

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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.

References

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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.

Kozhevnikova ZV; Kozhevnikov AE, 2009. Elodea densa (Hydrocharitaceae), a new adventive species for the flora of Asian Russia. Botanicheskii Zhurnal, 94(11):1705-1710.

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.

Rai AK; Pradhan BR, 2000. Aquatic weeds in the Lakes Phewa, Begnas and Rupa in Pokhara Valley, Nepal. Veterinary Review (Kathmandu), 15:10-12.

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.

Veldkamp JF, 2008. Egeria densa (Hydrocharitaceae), a new genus and species for Malesia. Flora Malesiana Bulletin, 14(3):156-159. http://www.nationaalherbarium.nl/fmbull/biblio.htm

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