Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Egeria densa
(leafy elodea)

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Datasheet

Egeria densa (leafy elodea)

Summary

  • Last modified
  • 19 November 2019
  • 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.
Copyright©Sheldon 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.
Copyright©Sheldon Navie
Habit showing dense mat of submerged foliage.
HabitHabit showing dense mat of submerged foliage.©Sheldon Navie
Flowers and leaves.
TitleFlowers
CaptionFlowers and leaves.
Copyright©Sheldon Navie
Flowers and leaves.
FlowersFlowers and leaves.©Sheldon Navie
Close-up of flower.
TitleFlower
CaptionClose-up of flower.
Copyright©Sheldon 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

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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

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Monocotyledonae
  •                     Order: Hydrocharitales
  •                         Family: Hydrocharitaceae
  •                             Genus: Egeria
  •                                 Species: Egeria densa

Notes on Taxonomy and Nomenclature

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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

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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

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Aquatic
Perennial
Seed propagated
Succulent
Vegetatively propagated

Distribution

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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.

Last updated: 30 Jun 2021
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

South AfricaPresent

Asia

GeorgiaPresent
IndonesiaPresentPresent based on regional distribution.
-SumatraPresent
JapanPresent
NepalPresent
TurkeyPresent

Europe

AustriaAbsent, Invalid presence record(s)
BelgiumPresent
FrancePresentIntroducedInvasive
GermanyPresentIntroducedInvasive
HungaryPresent
ItalyPresentIntroducedInvasive
NetherlandsPresentIntroducedInvasive
RussiaPresent
-Central RussiaPresent
-Russian Far EastPresent
SpainPresent, Localized
SwitzerlandPresentIntroducedInvasive
United KingdomPresentIntroducedInvasive

North America

Costa RicaPresentIntroduced
CubaPresentIntroducedInvasive
MexicoPresentIntroduced
NicaraguaPresentIntroduced
Puerto RicoPresentIntroducedInvasive
United StatesPresentPresent based on regional distribution.
-AlabamaPresentIntroducedInvasive
-ArizonaPresentIntroducedInvasive
-ArkansasPresentIntroducedInvasive
-CaliforniaPresentIntroducedInvasive
-ConnecticutPresentIntroducedInvasive
-DelawarePresentIntroducedInvasive
-FloridaPresentIntroducedInvasive
-GeorgiaPresentIntroducedInvasive
-HawaiiPresentIntroducedInvasive
-IllinoisPresentIntroducedInvasive
-KansasPresentIntroducedInvasive
-KentuckyPresentIntroducedInvasive
-LouisianaPresentIntroducedInvasive
-MarylandPresentIntroducedInvasive
-MassachusettsPresentIntroducedInvasive
-MississippiPresentIntroducedInvasive
-MissouriPresentIntroducedInvasive
-NebraskaPresentIntroducedInvasive
-New HampshirePresentIntroducedInvasive
-New JerseyPresentIntroducedInvasive
-New MexicoPresentIntroducedInvasive
-New YorkPresentIntroducedInvasive
-North CarolinaPresentIntroducedInvasive
-OklahomaPresentIntroducedInvasive
-OregonPresentIntroducedInvasive
-PennsylvaniaPresentIntroducedInvasive
-South CarolinaPresentIntroducedInvasive
-TennesseePresentIntroducedInvasive
-TexasPresentIntroducedInvasive
-UtahPresentIntroducedInvasive
-VermontPresentIntroducedInvasive
-VirginiaPresentIntroducedInvasive
-WashingtonPresentIntroducedInvasive

Oceania

AustraliaPresentPresent based on regional distribution.
-New South WalesPresentIntroduced
-TasmaniaPresentIntroduced
-VictoriaPresentIntroduced
-Western AustraliaPresentIntroduced
Cook IslandsPresentIntroducedInvasive
French PolynesiaPresentIntroducedInvasive
New ZealandPresentIntroducedInvasive

South America

ArgentinaPresentNative
BoliviaPresentIntroduced
BrazilPresent, LocalizedNative
-BahiaPresent
-Espirito SantoPresent, LocalizedNative
-GoiasPresent, LocalizedNative
-Mato Grosso do SulPresent, LocalizedNative
-Minas GeraisPresent, LocalizedNative
-ParanaPresent, LocalizedNative
-Rio de JaneiroPresent, LocalizedNative
-Santa CatarinaPresentNative
-Sao PauloPresent, LocalizedNative
ChilePresent
ColombiaPresentIntroduced
ParaguayPresent
UruguayPresentNative

History of Introduction and Spread

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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

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

Hosts/Species Affected

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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

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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

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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

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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

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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

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

Social Impact

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

Risk and Impact Factors

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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

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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

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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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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

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

Distribution References

Bini L M, Thomaz S M, 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 DOI:10.1016/j.aquabot.2005.06.010

CABI, Undated. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI

CABI, Undated a. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI

Cabrera AL, 1968. (Flora de la Provincia de Buenos Aires)., Buenos Aires, Argentina: INTA. 309-404.

Cabrera Walsh G, MagalíDalto Y, Mattioli F M, Carruthers R I, Anderson L W, 2013. Biology and ecology of Brazilian elodea (Egeria densa) and its specific herbivore, Hydrellia sp., in Argentina. BioControl. 58 (1), 133-147. DOI:10.1007/s10526-012-9475-x

Cook C D K, Urmi-König K, 1984. A revision of the genus Egeria (hydrocharitaceae). Aquatic Botany. 19 (43832), 73-96. DOI:10.1016/0304-3770(84)90009-3

EPPO, 2021. EPPO Global database. In: EPPO Global database, Paris, France: EPPO. https://gd.eppo.int/

Haramoto T, Ikusima I, 1988. Life cycle of Egeria densa planch., an aquatic plant naturalized in Japan. Aquatic Botany. 30 (4), 389-403. DOI:10.1016/0304-3770(88)90070-8

HEAR, 2002. Alien species in Hawaii. In: Hawaii Ecosystems at Risk, Honolulu, USA: Hawaii Ecosystems at Risk, University of Hawaii. http://www.hear.org/AlienSpeciesInHawaii/index.html

Kissmann KG, 1997. (Plantas Infestantes e Nocivas)., 1 (2) Brazil: BASF. 256-258.

Kozhevnikova Z V, Kozhevnikov A E, 2009. Elodea densa (Hydrocharitaceae), a new adventive species for the flora of Asian Russia. Botanicheskiĭ Zhurnal. 94 (11), 1705-1710.

Lagos N A, 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 DOI:10.1672/07-119.1

Missouri Botanical Garden, 2003. Vascular Tropicos database., St. Louis, USA: Missouri Botanical Garden. http://mobot.mobot.org/W3T/Search/vast.html

Oliveira N M B, Sampaio E V S B, Pereira S M B, Moura Junior A M, 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. DOI:10.1590/S0100-83582005000200026

Oviedo Prieto R, Herrera Oliver P, Caluff M G, 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 No. 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. 173-175.

Rai A K, Pradhan B R, 2000. Aquatic weeds in the Lakes Phewa, Begnas and Rupa in Pokhara Valley, Nepal. Veterinary Review (Kathmandu). 10-12.

Royal Botanic Garden Edinburgh, 2003. Database of European Plants (ESFEDS)., Edinburgh, UK: Royal Botanic Graden. 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. Hedychium flavescens. In: Germplasm Resources Information Network (GRIN). Online Database, Beltsville, USA: National Germplasm Resources Laboratory. http://www.ars-grin.gov/cgi-bin/npgs/html/tax_search.pl

USDA-NRCS, 2002. The PLANTS Database. Greensboro, North Carolina, USA: National Plant Data Team. https://plants.sc.egov.usda.gov

Veldkamp J F, 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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