Pacific Island Ecosystems at Risk (PIER)

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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 recourbee, amarante réfléchie

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)
Chile (continental)
Chile
Chile (Republic of) 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)
Colombia
Colombia
Colombia (Republic of) introduced
invasive
Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Ecuador (Mainland)
Ecuador
Ecuador (Republic of) (continental) 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 (country) introduced
invasive
Holm, Leroy/Doll, Jerry/Holm, Eric/Pancho, Jaun/Herberger, James (1997) (p. 55)
Japan
Japan
Japan (country) 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".
Perú
Perú
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 (except British Colombia)
Canada
Canada (country) 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).


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

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This page was created on 25 JAN 2007 and was last updated on 8 JAN 2011.