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)	New South Wales	introduced invasive	National Herbarium of New South Wales (2013) Naturalised
Australia Australia (continental)	Australia (continental)	introduced invasive	National Herbarium of New South Wales (2013) South Australia?, Tasmania, Victoria, Western Australia 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)
British Columbia (province of Canada) Province of British Columbia	Canada (British Columbia)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Central America Central America (Pacific rim)	El Salvador (Republic of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
Central America Central America (Pacific rim)	Nicaragua (Republic of)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
China China	China (People's Republic of)	introduced cultivated	Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013) Known from a cultivated fish pond, Guangdong.
Japan Japan	Japan	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)
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.