Myriophyllum spicatum L., Haloragaceae

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Present on Pacific Islands?  no

Primarily a threat at high elevations?  no

Risk assessment results:  Reject, score: 25 (Go to the risk assessment).

Common name(s): [more details]

Chinese: sui zhuang hu wei zao

English: Eurasian water milfoil, Eurasian watermilfoil, spike watermilfoil

Japanese: hozakinofusamo, kingyomo

Habit:  aquatic herb

Description:  "A perennial or biennial, submersed, aquatic herb; stems flexible, sparsely or much branched, slender, becoming leafless toward base, 1 to 4 m length, with extreme of 12 m reported from western Himalayas in Asia; adventitious roots on lower side of stem when on or in mud with additional at the upper surface prior to fragmentation; leaves dimorphic, grayish-green, in whorls of 4 to 5, usually with 14 to 24 pairs of filiform obtuse segments, 6 to 12 mm in length, extending outward from axis to give feather-like appearance; bracts inconspicuous, shorter than stem internodes; inflorescence borne on terminal spike of main stem and branches, 5 to 20 cm long, usually plink, below the spike are 5 to 20 nodes with diameter twice that of remainder of stem, rigid, lying parallel to water surface, spike erect at anthesis, parallel to water surface at fruit set; flowers, staminate flowers on upper axils; pistillate flowers below, often with bisexual flowers in the transition zone, flowers verticillate in whorls of 4, 2-ranked, lower 2 to 4 whorls of floral bracts usually comb-like, often longer than flowers, upper bracts entire, broader than long and shorter than flowers; staminate flower sepals ovate to triangular, 0.5 by 0.3 mm, erect, petals wine red, auriculate, 2.5 mm long, falling at anthesis, stamens 8; pistillate flower sepals strongly reduced, semiorbicular, erect, 0.2 to 0.3 mm, petals spreading, 0.3 to 0.5 mm, falling soon after anthesis; bisexual flower sepals and petals as in pistillate flowers, petals reddish; fruit muricate (a rough surface with sharp projections), globoseovoid, about 2.5 mm long, 4-grooved with 2 somewhat wrinkled ridges adjacent to lines of dehiscence, separating into 4 nut-like fruits"  (Holm et al., 1997; p. 482).

"Perennial aquatic herb with submerged stems to 2 m long.  Leaves in whorls of four, sessile, feathery; 2-3.5 cm long.  Inflorescence an aerial, terminal spike 3-8 cm long with 4 flowers at each node.  Female flowers in lower whorls with petals to 1 mm long; male flowers in upper whorls, with 4 reddish petals to 2.5 mm long, and 8 stamens.  Fruit ovoid, to 2.5 mm long, with 4 dry, 1-seeded nutlets."  (Waterhouse & Mitchell, 1998; pp 45-46).

Habitat/ecology:  "Freshwater wetlands, lakes, coastal estuaries.  This aquatic is most common in waters of 1-3 m depth, but can invasde waters up to 10 m deep.  It forms dense stands that shade out other species and alter the temperature profile of the water body.  It flourishes in lakes with nutrient rich water, and the spread of the plant is promoted by eutrophication"  (Weber, 2003; p. 278).  "Lakes, canals and reservoirs. Tolerates a wide pH range and brackish water. Can survive stranding, and depths up to 17 m. It chokes lakes and water storages, affecting fish and shellfish production, recreation and boat traffic." (Waterhouse & Mitchell, 1998; pp 45-46).

Propagation:  "Vegetative fragments and seed spread by moving water and water birds" (Waterhouse & Mitchell, 1998; pp 45-46).

Native range:  Eurasia (Waterhouse & Mitchell, 1998; pp 45-46).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
State of Hawaii Hawaiian Islands	Maui Island	introduced	Wester, Lyndon (1992) (p. 141)
Philippines Philippine Islands	Philippine Islands		Waterhouse, B. M./Mitchell, A. A. (1998) (p. 46)
Philippines Philippine Islands	Philippine Islands		Merrill, Elmer D. (1923) (p. 221) In shallow water of Lake Lanao, altitude 670 m.

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	U.S. Dept. Agr., Agr. Res. Serv. (2011) Naturalized
Cambodia Cambodia	Cambodia (Kingdom of)		Waterhouse, B. M./Mitchell, A. A. (1998) (p. 46)
Canada Province of British Columbia	Canada (British Columbia)		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 492)
Canada Canada	Canada (country)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)
China China	China (People's Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
China China	Hong Kong	native	Wu, Te-lin (2001) (p. 158)
Indonesia Indonesia	Indonesia (Republic of)		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 480)
Japan Japan	Japan (country)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
South Korea South Korea	South Korea (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 243)
Thailand Thailand	Thailand (Kingdom of)		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 480)
United States (west coast) United States (west coast states)	USA (Oregon)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)
United States (west coast) United States (west coast states)	USA (California)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)
United States (west coast) United States (west coast states)	USA (Washington)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)
Vietnam Vietnam	Vietnam (Socialist Republic of)		Waterhouse, B. M./Mitchell, A. A. (1998) (p. 46)

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. (2011)
United States (continental except west coast) United States (other states)	United States (other states)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2011) Naturalized
United States (continental except west coast) United States (other states)	USA (Florida)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)

Comments:  "A serious weed in South Africa and USA, and a principal weed in India" (Waterhouse & Mitchell, 1998; pp 45-46).

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

Physical:  "Plants can be removed by mechanical harvesters, although this may enhance stem fragmentation".

Chemical:  "The plant is highly susceptible to 2,4-D.  Regrowth is fast if plants are not killed, and repeated control is necessary"  (Weber, 2003; p. 278).

Additional information:
Fact sheet from the Plant Conservation Alliance, Alien Plant Working Group.
Information from the Global Invasive Species Database.
Information from the Southeast Exotic Pest Plant Council Invasive Plant Manual.
See information in the book "Biology and control of aquatic plants: A best management practices handbook"  (large file, PDF format).

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

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

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

References:

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.

Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James. 1997. World weeds: natural histories and distribution. John Wiley & Sons. 1129 pp.

Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. 1979. A geographical atlas of world weeds. John Wiley & Sons, New York. 391 pp.

Merrill, Elmer D. 1923. An enumeration of Philippine flowering plants, vol. 3 [reprint]. Bureau of Printing, Manila. 628 pp.

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

U.S. Dept. Agr., Nat. Res. Cons. Serv. 2011. The PLANTS Database. National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Van Driesche, Roy/Lyon, Suzanne/Blossey, Bernd/Hoddle, Mark/Reardon, Richard. 2002. Biological control of invasive plants in the eastern United States. USDA Forest Service Publication FHTET-2002-04. 413 pp.

Waterhouse, B. M./Mitchell, A. A. 1998. Northern Australia Quarantine Strategy: weeds target list. Second edition. Australian Quarantine & Inspection Service, Miscellaneous Publication No. 6/98. 110 pp.

Weber, Ewald. 2003. Invasive plants of the World. CABI Publishing, CAB International, Wallingford, UK. 548 pp.

Wester, Lyndon. 1992. Origin and distribution of adventive flowering plants in Hawai‘i. In: Stone, Charles P.; Smith, Clifford W. and Tunison, J. Timothy. Alien plant invasions in native ecosystems of Hawaii: Management and Research. University of Hawaii, Cooperative National Park Research Studies Unit, Honolulu. University of Hawaii Press. .

Wu, Te-lin. 2001. Check List of Hong Kong Plants. Hong Kong Herbarium and the South China Institute of Botany. Agriculture, Fisheries and Conservation Department Bulletin 1 (revised). 384 pp.

Zhengyi, Wu/Raven, Peter H./Deyuan, Hong. 2011. Flora of China (online resource).