Pacific Island Ecosystems at Risk (PIER)

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Hydrilla verticillata
(dummy value for TaxonCode Authority; this value should be replaced!!).......Hydrocharitaceae


Reject, score: 20 (Go to the risk assessment)

Chinese: hei zao

English: Florida elodea, hydrilla, Indian stargrass, water thyme, water weed

Japanese: kuromo

Tagalog: ináta, lomolomótan

"A wholly submerged branching perennial herb...  Stems:  Pale green, vertical, slender, branching above and rooting freely from the lower nodes, to 8 m long depending on water depth; stolons, which are short slender lateral stems, form on or slightly below the surface of the bottom mud.  Vegetative reproductive organs, tubers and turions are produced, respectively, on the stolon and stem apices and as short lateral branches along the upper stems.  Leaves:  Pale to bright green, often red-streaked on the prominent midrib and margins, sessile; upper leaves in distinct whorls of 4 to 6, sometimes 3 to 8, linear-lanceolate, 1 to 3 cm long, margins with strong forward-pointing teeth; lower leaves smaller and fewer, often in opposite pairs only.  Flowers:  Solitary, inconspicuous, 3 mm across, exserted from spathes in leaf axils and carried to the surface on thread-like perianth tubes (hypanthia), perianth segments 6; female flower, spathe sessile, usually one in each leaf whorl, 3 filamentous stigmas, male flower, exserted from spathes on short stems, usually several to each leaf whorl, stamens 3.  Fruit:  Cylindrical, 5 to 15 mm long, 3 to 6 mm diameter, develops within spathe and contains 0 to 6 seeds.  Seed:  Green to dark brown, shiny, 2 to 2.5 mm long, seedcoat extended at each end.  Root:  Filamentous, rising from the lower stem nodes"  (Parsons and Cuthbertson, 1992; pp. 567-570). Warm freshwater ponds and slow-moving streams.  Can grow in cool and brackish water.  The plant is normally firmly rooted in the bottom mud but occasionally breaks free and forms free-floating mats.

In Fiji, "near sea level, forming extensive mats in ditches and pools, and also in freshwater rivers and streams, and carried into saltwater bays by floods.  The species has become a very serious weed of many rivers on Viti Levu, especially those of the Rewa system, where it sometimes fouls the propellers of launches and outboard motors"  (Smith, 1979; pp. 125-127). In New Caledonia, "localement abondant dans des mares et des ruisseaux à courant faible" (MacKee, 1994; p. 66). Reproduces both sexually and asexually. Male and female flowers are usually borne on separate plants but occasionally plants are bisexual. Local extension may occur from tubers and stolons. Most commonly, pieces break free and float to new locations. Europe, Africa, Asia, Australia; exact native range obscure; also cultivated and naturalized (GRIN).
Pacific
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
Fiji
Fiji Islands
Viti Levu Island introduced
invasive
Smith, Albert C. (1979) (pp. 125-127)
Vouchers cited: G. Dennis 955, DA 16032, DA 16033, DA 13566, DA 16629, DA 16610, DA 16608, DA 16612, DA 16645, DA 16627, DA 16604, DA 16609, DA 16603, DA 16657, DA L.15601
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1968) (voucher ID: BISH 33986)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1968) (voucher ID: BISH 33987)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1969) (voucher ID: BISH 33989)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1969) (voucher ID: BISH 33990)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1968) (voucher ID: BISH 33991)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1968) (voucher ID: BISH 33992)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1942) (voucher ID: BISH 112348)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Fiji
Fiji Islands
Viti Levu Island   Bishop Museum (Honolulu) (1970) (voucher ID: BISH 699483)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Guam
Guam Island
Guam Island native
Stone, Benjamin C. (1970) (p. 102)
Also as Egeria densa sensu Stone (Fosberg, 1987). Vouchers cited: Stone 4468 (GUAM), Stone 4305 (GUAM)
Guam
Guam Island
Guam Island introduced
Fosberg, F. R./Sachet, Marie-Hélène/Oliver, Royce (1987) (p. 29)
Guam
Guam Island
Guam Island   Bishop Museum (Honolulu) (1962) (voucher ID: BISH 112263)
Taxon name on voucher: Egeria densa Planch.
Guam
Guam Island
Guam Island   Bishop Museum (Honolulu) (1962) (voucher ID: BISH 112341)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Guam
Guam Island
Guam Island   Bishop Museum (Honolulu) (1978) (voucher ID: BISH 438117)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Guam
Guam Island
Guam Island   Bishop Museum (Honolulu) (1983) (voucher ID: BISH 649480)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
Guam
Guam Island
Guam Island   Bishop Museum (Honolulu) (1983) (voucher ID: BISH 1000193)
Taxon name on voucher: Hydrilla verticillata (L.) Hoyle
State of Hawaii
Hawaiian Islands
Hawaiian Islands introduced
cultivated
Staples, George W./Herbst, Derral/Imada, Clyde T. (2000) (p. 22)
New Caledonia
New Caledonia
New Caledonia Islands   Swarbrick, John T. (1997) (p. 92)
New Caledonia
New Caledonia
New Caledonia Islands introduced
Meyer, Jean-Yves (2000) (p. 100)
"Potential invader".
New Caledonia
New Caledonia Archipelago
Île Grande Terre introduced
invasive
MacKee, H. S. (1994) (p. 66)
Vouchers cited: MacKee 14782, Veillon 1139 (NOU), MacKee 22542, MacKee 34796, MacKee 38205
Papua New Guinea
Papua New Guinea (eastern New Guinea Island)
Papua New Guinea (eastern New Guinea Island) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines
Philippine Islands
Philippine Islands native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Philippines
Philippine Islands
Philippine Islands   Merrill, Elmer D. (1925) (p. 26)
In shallow fresh water at low and medium altitudes; often abundant.
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) native
National Herbarium of New South Wales (2013)
South Australia, Victoria, Western Australia
Australia
Australia (continental)
New South Wales native
National Herbarium of New South Wales (2013)
Australia
Australia (continental)
Northern Territory native
National Herbarium of New South Wales (2013)
Australia
Australia (continental)
Queensland native
National Herbarium of New South Wales (2013)
Cambodia
Cambodia
Cambodia (Kingdom of)   Waterhouse, D. F. (1993) (pp. 66, 77)
China
China
China (People's Republic of) native
Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013)
Ponds, running water. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Liaoning, Shaanxi, Shandong, Sichuan, Xizang, Yunnan, Zhejiang.
China
China
Hong Kong introduced
cultivated
Wu, Te-lin (2001) (p. 292)
Colombia
Colombia
Colombia (Republic of)   Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 393)
Indonesia
Indonesia
Indonesia (Republic of) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Japan
Japan
Japan (country) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
North Korea
North Korea
North Korea (Democratic People's Republic of) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
South Korea
South Korea
South Korea (Republic of) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Malaysia
Malaysia
Malaysia (country of) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Mexico
Mexico
Mexico (United Mexican States) introduced
invasive
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Naturalized
Negara Brunei Darussalam
Brunei
Brunei (Negara Brunei Darussalam)   Waterhouse, D. F. (1993) (pp. 66, 77)
New Zealand
New Zealand
New Zealand (country) introduced
invasive
Owen, S. J. (1997)
Panama
Panama
Panama (Republic of) introduced
invasive
Cronk, Q. C. B./Fuller, J. L. (2001) (p. 162)
Singapore
Singapore
Singapore (Republic of)   Waterhouse, D. F. (1993) (pp. 66, 77)
Singapore
Singapore
Singapore (Republic of) uncertain if introduced
invasive
Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 49)
Weed of uncertain origin
Taiwan
Taiwan Island
Taiwan Island native
Zhengyi, Wu/Raven, Peter H./Deyuan, Hong (2013)
Ponds, running water.
Thailand
Thailand
Thailand (Kingdom of) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (west coast)
United States (west coast states)
USA (California) introduced
invasive
Cronk, Q. C. B./Fuller, J. L. (2001) (p. 162)
United States (west coast)
United States (west coast states)
USA (Washington) introduced
U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Vietnam
Vietnam
Vietnam (Socialist Republic of) native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Indian Ocean
Country/Terr./St. &
Island group
Location Cited status &
Cited as invasive &
Cited as cultivated &
Cited as aboriginal introduction?
Reference &
Comments
La Réunion (France)
La Réunion Island
La Réunion Island native
Comité français de l'Union Internationale pour la Conservation de la Nature en France (2013)
Mascarene Islands
Mascarene Islands (Mauritius, La Reunion, Rodrigues)
Mascarene Islands introduced
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Mauritius
Mautitius Islands (Mauritius and Rodrigues)
Mauritius Island native
U.S. Dept. Agr., Agr. Res. Serv. (2013)
Seychelles
Seychelles Islands
Seychelles Islands introduced
U.S. Dept. Agr., Agr. Res. Serv. (2013)
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
invasive
Cronk, Q. C. B./Fuller, J. L. (2001) (p. 162)
Planting of this species in the State of Florida (U.S.) is prohibited by Florida Department of Environmental Protection (Hunsberger, 2001). See "Biology and control of aquatic plants: A best management practices handbook"  for control information (large file, PDF format).

Additional control information from the Bugwood Wiki.

Physical: Mechanical methods are usually only temporarily effective, and may serve to spread the plant.

Chemical: "In flowing water acrolein is used extensively, and controlled delivery of fluridone, as the newly developed fibre formulations, has been effective in the United states.  In ponded waters overseas, chelated copper compounds, diquat, paraquat, diuron and granular formulations of endothal and 2,4-D have given good control.  The length of exposure required to give effective control varies with the herbicide used, the bipyridyls, diquat and paraquat, usually giving the quickest kill" (Parsons and Cuthbertson, 1992; pp. 567-570).

Biological: The white amur or Chinese grass carp has been used, but this species of fish is invasive in some instances. OK if sterile (triploid) fish are used. Several insects are under investigation in the US (Julien, 1992; pp. 69-70).  "In the USA, Paraponyx diminutalis (Lpidoptera:Pyralidae) was introduced accidentally; it causes some damage but does not result in full control" (Cronk & Fuller, 2001: p. 162).

Biological control information from the publication "Biological control of invasive plants in the eastern United States".


Need more info? Have questions? Comments? Information to contribute? Contact PIER! (pier@hear.org)

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