Amaranthus retroflexus L., Amaranthaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Common name(s): [more details]

Chinese: fan zhi xian

English: American pigweed, careless weed, common amaranth, pigweed redroot, redroot, redroot amaranth, redroot pigweed, reflexed amaranth, rough pigweed, wild-beet amaranth

French: amarante réfléchie, amarante recourbee

Japanese: aogeito

Spanish: amaranto, amaranto común, atacu, bledo, marxant, moco de pavo, penacho, quelite, yuyo

Habit:  herb

Description:  "A monoecious, erect, finely hairy, freely-branching, herbaceous annual growing up to 2 m tall; taproot pink or red, depth varies with soil profile; leaves alternate, egg-shaped or rhombic-ovate, cuneate at base, up to 10 cm long, margins somewhat wavy, veins prominent on underside, apex may be sharp, petiole shorter or longer than leaf; flowers numerous, small, borne in dense blunt spikes 1 to 5 cm long, densely crowded onto terminal panicle 5 to 20 cm long but may be smaller on upper axils; 3 spiny-tipped, rigid, awl-shaped bracts surround the flower, exceeding calyx, length 4 to 8 mm, persistent; tepals 5, much longer than fruit, usually definitely recurved at tips, obovate or highly spatulate, 1 pistil and 5 stamens; style branches erect or a bit recurved; fruit a utricle, membranous, flattened, 1.5 to 2 mm long, dehiscing by a transverse line at the middle, wrinkled upper part falling away; seed oval to egg-shaped, somewhat flattened, notched at the narrow end, 1 to 1.2 mm long, shiny black or dark red-brown.  The species can be initially identified by the rounded (not pointed) shape of its recurved tepals and the shorter, more crowded branches of its inflorescence, and if nee be by a more detailed examination of the floral structures"  (Holm et al., 1997; pp. 51, 53).

Habitat/ecology:  "The weed thrives in cultivated fields, home gardens, waste places and on ditch banks.  It prefers open, sunny areas and appears quickly when soil is disturbed" (Holm et al., 1997; p. 56).

Propagation:  Seed

Native range:  North America, naturalized nearly worldwide (GRIN).

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./Shannon, Robynn K./Herbst, Derral R. (1997) (p. 51) Voucher cited: Herbst 5907 (US) Apparently naturalized, present status unknown.
Philippines Philippine Islands	Philippine Islands	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)

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	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Australia Australia (continental)	Queensland	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
China China	China (People's Republic of)	introduced invasive	Li-ying, Li/Ren, Wang/Waterhouse, D. F. (1997) (p. 172)
China China	China (People's Republic of)	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Indonesia Indonesia	Indonesia (Republic of)	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Japan Japan	Japan	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Japan Japan	Japan	introduced	Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 182)
South Korea South Korea	South Korea (Republic of)	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013) Coahuila
New Zealand New Zealand	New Zealand (country)	introduced invasive	Webb, C. J./Sykes, W. R./Garnock-Jones, P. J. (1988) (p. 107) "Waste places, cultivated ground".
South America (Pacific rim) South America (Pacific rim)	Chile (Republic of)	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
South America (Pacific rim) South America (Pacific rim)	Colombia	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
South America (Pacific rim) South America (Pacific rim)	Ecuador (Republic of) (continental)	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
South America (Pacific rim) South America (Pacific rim)	Perú (Republic of)	introduced invasive	Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)

Also reported from
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Canada Canada	Canada	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (continental except west coast) United States (other states)	United States (other states)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (continental except west coast) United States (other states)	USA (Florida)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)

Control:  Some varieties have developed resistance to herbicides (Holm et al., 1997; pp. 63-64).