Myriophyllum aquaticum (Vell.) Verdc., Haloragaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results: 

High risk, score: 22 (Go to the risk assessment (Pacific)).
Reject, score: 20 (Go to the risk assessment (Australia)).

Common name(s): [more details]

English: Brazilian water milfoil, parrot's feather, water feather, water milfoil

French: myriophylle du Brésil

Habit:  aquatic herb

Description:  "A bright or glaucous green perennial freshwater herb that, extending from the bank or rising up through several meters of water, forms vigorous mats of tangled stems.  The species normally produces male and female flowers on separate plants but occasionally plants bearing flowers of both sexes occur.  Stems:  Yellow-green, slender, from 2 to 5 m long, creeping and rooting at the nodes near the base. Leaves bright glaucous green; feathery in appearance, in whorls of 4 to 6, distant near the base of the stem, densely packed towards the apex; broadly linear or elliptical in outline, 3 to 3.5 cm long, deeply divided into 10 to 14 pairs of thread-like segments; submerged leaves tend to decay with time leaving more or less bare stems.  Flowers solitary, risking on short stalks between 2 small bracts about 1.5 mm long in the upper leaf axils; sepals 4, white-translucent, 1 to 1.5 mm long; petals absent; stigmas prominent, bearing numerous fine white-translucent hairs; male flowers not recorded from Australia.  Fruit and seed:  Not known in Australia.  Root:  Fine and thread-like, rising from the nodes"  (Parsons and Cuthbertson, 1992; pp. 485-487).

Habitat/ecology:  Freshwater streams and adjacent saturated mud or gravel.  Tolerates a wide range of temperatures, but most prolific in the tropics.  "Freshwater wetlands, ponds, streams and lakes.  The plant has aerial stems floating on the water surface but grows also as a submerged plant.  It rapidly colonizes wetlands and forms dense stands that exclude native water plants.  Light is strongly reduced and water flow impeded"  (Weber, 2003; p. 277).

In Hawai‘i, "naturalized in permanent standing or running water, especially in taro paddies and pastures, 0-1,280 m"  (Wagner et al., 1999; p. 792).

Propagation:  Stem fragments. Widely distributed through the aquarium trade and spread as a result of aquarium dumping plants.

Native range:  South America.

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	Hawai‘i (Big) Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 792)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 792)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wagner, Warren L./Herbst, Derral R./Sohmer, S. H. (1999) (p. 792) Voucher cited: Forbes 2562.O (BISH)

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	Cronk, Q. C. B./Fuller, J. L. (2001) (p. 172)
Australia Australia (continental)	Queensland	introduced invasive	Cronk, Q. C. B./Fuller, J. L. (2001) (p. 172)
Chile (continental) Chile	Chile (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Ecuador (Mainland) Ecuador	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Owen, S. J. (1997)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 754) "Aerial or submerged in lake margins and slowly flowing rivers".
Perú Perú	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
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)

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	introduced invasive cultivated	Lavergne, Christophe (2006) "Cultivé/±envahissant"

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)	USA (Florida)	introduced	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2011)

Control: 

Physical: "1. Rake up (November-January): Leave on site to rot down. away from water, and then follow up from February to April by spraying any regrowth. 
2. Weedmat: Lay carefully to ensure fragments are not released, start at top of infestation, leave 3-4 months. 3. Lower water level, mechanically remove, use weedmat to cover the area or dry out thoroughly for 2-3 weeks"  (Weedbusters New Zealand).

Chemical: Herbicides (glyphosate, chlorsulfuron, 2,4-D) are effective but the presence of water may limit their use. Glyphosate 2% + 0.2% Pulse sprayed 4 times over a10+ week period (Smart, 1991, in Timmins and Mackenzie, 1995; pp. 183-185).

"Spray terrestrial sites (spring-autumn): glyphosate (20ml/L + penetrant) sprayed 4 times over a 10 or more week programme"  (Weedbusters New Zealand).

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

Additional information:
Photos and additional information at University of Florida, Center for Aquatic and Invasive Plants.
Fact sheet from the Bay of Plenty Regional Council, New Zealand.
Photos and additional information at the Environment Bay of Plenty, New Zealand, web site of the Bay of Plenty Regional Council.
Draft European and Mediterranean Plant Protection Organization datasheet.
Information from the Global Invasive Species Database.
Information sheet from Weedbusters New Zealand.
Photos and other information from Chileflora.

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

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

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

References:

Cronk, Q. C. B./Fuller, J. L. 2001. Plant invaders. Earthscan Publications, Ltd., London. 241 pp.

Lavergne, Christophe. 2006. List des especes exotiques envahissantes a La Reunion. Unpublished manuscript (Excel file). .

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

Parsons, W. T./Cuthbertson, E. G. 1992. Noxious weeds of Australia. Inkata Press, Melbourne/Sydney. 692 pp.

Timmins, S. M./Mackenzie, I. W. 1995. Weeds in New Zealand protected natural areas database. Wellington, New Zealand. Department of Conservation, , Technical Series No. 8. 287 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.

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).

Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. 1988. Flora of New Zealand, Volume IV: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch. 1365 pp.

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