Alternanthera philoxeroides (Mart.) Griseb., Amaranthaceae

Click on an image for links to BIGGER PICTURES

Present on Pacific Islands?  no

Primarily a threat at high elevations?  no

Risk assessment results:  Reject, score: 22 (Go to the risk assessment)

Other Latin names:  Bucholzia philoxeroides Mart.

Common name(s): [more details]

Chinese: xi han lian zi cao

English: alligator grass, alligator weed

Spanish: lagarto

Habit:  herb

Description:  "Perennial herb; stems creeping or floating, ascending towards apex, rooting at the lower nodes, branched, hollow, with a longitudinal hairy groove on 2 opposite sides.  Leaves subsessile or with petiole to 5 mm long, with a ring of white hairs between the 2 opposite leaf bases.  Lamina 3-13 x 1-3.5 cm, elliptic to oblanceolate or obovate, glabrous or slightly hairy near the attenuate base; apex obtuse or acute.  Inflorescences in upper axils, mostly 1-2 cm in diameter, capitate, white; pedicles to 9 cm long with 2 opposite longitudinal hairy grooves, occasionally heads shortly pedunculate and terminal.  Bracts 2.5-3.5 mm long, ovate-acuminate; bracteoles similar to bracts, somewhat smaller, persistent.  Tepals 5-7 mm long, oblong to ovate, acute or obtuse.  Fertile stamens 5; staminodes = stamens.  Style short, thick; stigma capitate."  (Webb et al, 1988; p. 101).

Habitat/ecology:  "The plant grows best in aquatic sites but may establish as a terrestrial species in wet and poor pastures and on irrigated lands.  The weed prefers level areas of shore or shallow water where it is protected from wave erosion.  As with many weeds it thrives in eutrophic conditions and thus often increases where urban and industrial development have polluted and degraded water quality.  Severe storms may strip the leaves from anchored mats or tear the tangled vegetation loose and move it to a new location.  Terrestrial pants may remain under water for several days without ill effects.  The plant prefers fresh water but is found along the inland tidal reaches of rivers that run to the sea.  In summary, alligatorweed probably grows in a wider range of water and soil conditions than any other major aquatic weed.  Its growth is equally startling whether free floating, loosely attached and forming a mat, or as an emersed plant in a wet or relatively dry field.  It loves fresh water of high fertility but can tolerate saline soils and waters"  (Holm et al., 1997; pp. 39-40).  "...can grow as either a trailing, terrestrial herb or as a floating aquatic (usually attached to the bank)" (Csurhes & Edwards, 1998; p. 137).  A serious problem in waterways in tropical and warm-temperate regions of the world.

In New Zealand, "drains, streams, swamps and similar wet places. Alligator weed forms dense floating mats in stagnant or slow moving water, and also grows in dune hollows behind beaches" (Webb et al., 1988; p. 101).

Propagation:  Primarily by stem fragments carried by water (Csurhes & Edwards, 1998; p. 137).

Native range:  South America; cultivated and naturalized elsewhere (GRIN).

Presence:

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 cultivated	Csurhes, S./Edwards, R. (1998) (p. 137)
Australia Australia (continental)	Queensland	introduced cultivated	Csurhes, S./Edwards, R. (1998) (p. 137)
Central America Central America (Pacific rim)	Honduras (Republic of)		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 16)
China China	China (People's Republic of)	introduced invasive	Li-ying, Li/Ren, Wang/Waterhouse, D. F. (1997) (pp. 172, 178)
China China	Hong Kong	introduced invasive	Wu, Te-lin (2001) (p. 77) In wet places.
Indonesia Indonesia	Indonesia (Republic of)	introduced invasive	Csurhes, S./Edwards, R. (1998) (p. 137)
Japan Japan	Japan	introduced	Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 182)
Mexico Mexico	Mexico (United Mexican States)		Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (pp. 37, 44)
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 101)
Singapore Singapore	Singapore (Republic of)	introduced invasive	Chong, Kwek Yan/Tan, Hugh T. W./Corlett, Richard T. (2009) (p. 12) Naturalised
South America (Pacific rim) South America (Pacific rim)	Colombia		Holm, Leroy/Pancho, Juan V./Herberger, James P./Plucknett, Donald L. (1979) (p. 16)
South America (Pacific rim) South America (Pacific rim)	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Taiwan Taiwan Island	Taiwan Island	introduced invasive	Li-ying, Li/Ren, Wang/Waterhouse, D. F. (1997) (pp. 172, 178)
Thailand Thailand	Thailand (Kingdom of)	introduced invasive	Csurhes, S./Edwards, R. (1998) (p. 137)
United States (west coast) United States (west coast states)	USA (California)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
Vietnam Vietnam	Vietnam (Socialist Republic of)		Waterhouse, D. F. (1993) (p. 63)

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 invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)
United States (continental except west coast) United States (other states)	USA (Florida)	introduced invasive	U.S. Dept. Agr., Nat. Res. Cons. Serv. (2013)

Comments:  Listed as a noxious weed in Australia and New Zealand.  A "weed of national significance" in Australia.

Control:  For additional control information see the information sheet from Weedbusters New Zealand.

Physical: Attempts at physical control usually only serve to spread the weed.

Chemical: Resistant to most herbicides. "Dicamba, triclopyr, and bentazone are used to control this plant" (Weber, 2003; p. 40).

Biological: A biological control program has been initiated in New South Wales, Australia. A beetle (Agasicles hygrophila) is somewhat successful in controlling the aquatic form, but does not control the terrestrial form (Csurhes & Edwards, 1998; p. 137). Use of this agent has been successful in New Zealand and Thailand (Julien, 1992; p. 1-3).

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