Pacific Island Ecosystems at Risk (PIER)

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Egeria densa
Planch., Hydrocharitaceae
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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results: 

Australia:  Reject, score: 22 (Go to the risk assessment)
Risk assessment from the Government of Queensland, Australia (PDF format).

Other Latin names:  Elodea densa (Planch.) Casp.

Common name(s): [more details]

Chinese: shui yun cao

English: Brazilian elodea, Brazilian waterweed, dense waterweed, egeria, large-flower waterweed, leafy elodea

Habit:  aquatic herb

Description:  "Submerged, rooted or drifting aquatics of fresh water.  Stems cylindric, simple or branched; lower leaves opposite or in whorls of 3, upper leaves in whorls of 4-8, linear to ovate serrulate; flowers dioecious; staminate flowers 2-4 together within spathe; petals 3, white; stamens 9, pistillate flowers on slender hypanthium-base; sepals 3; petals 3, stigma trifid; ovary 1-celled; ovules several on 3 linear placentae; fruit a transparent capsule" (Stone, 1970; p. 101).

Habitat/ecology:  Shallow, still water of lakes or streams. Forms dense mats displacing native species, depleting oxygen and otherwise changing the character of streams and lakes. In Hawai‘i, "sparingly naturalized in ponds and perhaps also slow-running ditches" (Wagner et al., 1999; p. 1443).

Propagation:  Pieces and cuttings, often spread by dumping of aquarium plants.

Native range:  Argentina, Brazil, Uruguay; cultivated elsewhere and widely naturalized (GRIN).

Presence:

Pacific
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Cook Islands
Southern Cook Islands
Rarotonga Island   McCormack, Gerald (2013)
French Polynesia
Society Islands
Tahiti Island introduced
invasive
cultivated
Welsh, S. L. (1998) (p. 349)
Vouchers cited: Fosberg 62976, Florence 4622, Florence 3165
French Polynesia
Society Islands
Tahiti Island introduced
invasive
Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. (2013)
Vouchers cited: J. Florence 3165 (PAP), J. Florence 4622 (PAP), W.A. Whistler & M. Guérin 1 (PAP) (as Hydrilla verticillata (L.) Presl)
Naturalisé. Menace pour la biodiversité.
French Polynesia
Society Islands
Tahiti Island   Bishop Museum (Honolulu) (1983) (voucher ID: BISH 554435)
Taxon name on voucher: Egeria densa Planch.
French Polynesia
Society Islands
Tahiti Island   Bishop Museum (Honolulu) (1982) (voucher ID: BISH 699484)
Taxon name on voucher: Egeria densa Planch.
French Polynesia
Society Islands
Tahiti Island   National Tropical Botanical Garden (U.S.A. Hawaii. Kalaheo.) (1981) (voucher ID: PTBG 37268)
Taxon name on voucher: Egeria densa
State of Hawaii
Hawaiian Islands
Hawai‘i (Big) Island introduced
invasive
cultivated
Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1443)
State of Hawaii
Hawaiian Islands
Kaua‘i Island introduced
invasive
cultivated
Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1443)
State of Hawaii
Hawaiian Islands
Maui Island introduced
invasive
Oppenheimer, Hank L. (2003) (p. 14)
West Maui. Voucher cited: Oppenheimer, L. Nelson & F. Duvall H110002 (BISH, PTBG)
State of Hawaii
Hawaiian Islands
Moloka‘i Island introduced
invasive
cultivated
Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1443)
State of Hawaii
Hawaiian Islands
O‘ahu Island introduced
invasive
cultivated
Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 1443)
Pacific Rim
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Australia
Australia (continental)
Australia (continental) introduced
invasive
National Herbarium of New South Wales (2013)
South Australia?, Tasmania, Victoria, Western Australia
Naturalised
Australia
Australia (continental)
New South Wales introduced
invasive
National Herbarium of New South Wales (2013)
Naturalised
Australia
Australia (continental)
Northern Territory introduced
invasive
National Herbarium of New South Wales (2013)
Naturalised
Australia
Australia (continental)
Queensland introduced
invasive
Queensland Herbarium (2002) (p. 3)
Canada (British Colombia)
Province of British Columbia
Canada (British Columbia) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
China
China
China (People's Republic of) introduced
cultivated
Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013)
Known from a cultivated fish pond, Guangdong.
El Salvador
El Salvador
El Salvador (Republic of) introduced
invasive
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Naturalized
Japan
Japan
Japan (country) introduced
Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 190)
Mexico
Mexico
Mexico (United Mexican States) introduced
invasive
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Naturalized
New Zealand
New Zealand
New Zealand (country) introduced
invasive
Healy, A. J./Edgar, E. (1980) (p. 26)
Voucher cited: B. E. G. Molesworth (AK 140634)
New Zealand
New Zealand
New Zealand (country) introduced
invasive
Owen, S. J. (1997)
Nicaragua
Nicaragua
Nicaragua (Republic of) introduced
invasive
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Naturalized
United States (west coast)
United States (west coast states)
USA (Oregon) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (west coast)
United States (west coast states)
USA (California) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (west coast)
United States (west coast states)
USA (Washington) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Indian Ocean
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Australia (Indian Ocean offshore islands)
Christmas Island Group
Christmas Island introduced
cultivated
Swarbrick, J. T. (1997) (p. 112)
Also reported from
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
United States (continental except west coast)
United States (other states)
United States (other states) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (continental except west coast)
United States (other states)
USA (Florida) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)

Comments:  Recently discovered in French Polynesia (Jean-Yves Meyer, personal communication).

Control:  See "Biology and control of aquatic plants: A best management practices handbook"  for control information (large file, PDF format).

Chemical: Diquat (Reglone) or acrolein.

Additional information:
Information on the Environment Bay of Plenty, New Zealand, web site.
Fact sheet from the Bay of Plenty Regional Council, New Zealand.
Photo at University of Florida, Center for Aquatic and Invasive Plants.
Information from the Global Invasive Species Database.
Fact sheet from the Government of Queensland, Australia. (PDF format).
Information sheet from Weedbusters New Zealand.
See information in the book "Biology and control of aquatic plants: A best management practices handbook"  (large file, PDF format).

Additional online information about Egeria densa is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Egeria densa as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Egeria densa may be available from the Germplasm Resources Information Network (GRIN).

References:

Bishop Museum (Honolulu). 1982. Voucher specimen #BISH 699484 (Florence, J. 3165).

Bishop Museum (Honolulu). 1983. Voucher specimen #BISH 554435 (Florence, J. 4622).

Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. 2013. Base de données botaniques Nadeaud de l'Herbier de la Polynésie Française (PAP). (online resource).

Gettys, Lyn A./Haller, William T./Bellaud, Marc; eds. 2009. Biology and control of aquatic plants: A best management practices handbook. Aquatic Ecosystem Restoration Foundation, Marietta, Georgia. ISBN 978-0-615-32646-7. 200 pp.

Healy, A. J./Edgar, E. 1980. Flora of New Zealand, Volume III: Adventive cyperaceous, petalous & spathaceous monocotyledons. Government Printer, Wellington, New Zealand. 220 pp.

McCormack, Gerald. 2013. Cook Islands Biodiversity Database, Version 2007.2. Cook Islands Natural Heritage Trust, Rarotonga.

Mito, Toshikazu/Uesugi, Tetsuro. 2004. Invasive alien species in Japan: the status quo and the new regulation for prevention of their adverse effects. Global Environmental Research 8(2)/2004: 171-191.

National Herbarium of New South Wales. 2013. PlantNet: New South Wales Flora online. The Plant Information Network System of the Botanic Gardens Trust Version 2.0. Online resource.

Oppenheimer, Hank L. 2003. New plant records from Maui and Hawai‘i Counties. In: Evenhuis, Neal L. and Eldredge, Lucius G., eds. Records of the Hawaii Biological Survey for 2001-2002. Part 1: Articles. Bishop Museum Occasional Papers. 73:3-30.

Owen, S. J. 1997. Ecological weeds on conservation land in New Zealand: A database. Working draft. Wellington, New Zealand. Department of Conservation.

Queensland Herbarium. 2002. Invasive Naturalised Plants in Southeast Queensland, alphabetical by genus. Modified from: Batianoff, George N. and Butler, Don W. (2002). Assessment of Invasive naturalized plants in south-east Queensland. Appendix. Plant Protection Quarterly 17, 27-34. 11 pp.

Stone, Benjamin C. 1970. The flora of Guam. Micronesica 6:1-659.

Swarbrick, J. T. 1997. Environmental weeds and exotic plants on Christmas Island, Indian Ocean: a report to Parks Australia. 101 pp. plus appendix.

U.S. Dept. Agr., Agr. Res. Serv. 2013. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

U.S. Dept. Agr., Nat. Res. Cons. Serv. 2013. The PLANTS Database. National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. 1999. Manual of the flowering plants of Hawaii. Revised edition. Bernice P. Bishop Museum special publication. University of Hawai‘i Press/Bishop Museum Press, Honolulu. 1919 pp. (two volumes).

Welsh, S. L. 1998. Flora Societensis: A summary revision of the flowering plants of the Society Islands. E.P.S. Inc., Orem, Utah. 420 pp.

Zhengyi, Wu/Raven, Peter H./Deyuan, Hong. 2013. Flora of China (online resource).


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This page was created on 1 JAN 1999 and was last updated on 20 APR 2013.