Ambrosia psilostachya DC., Asteraceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Risk assessment results:  High risk, score: 15 (Go to the risk assessment)

Other Latin names:  Ambrosia coronopifolia Torr. & A. Gray

Common name(s): [more details]

English: Dunbible-weed, Roman wormwood, artemisia, cuman ragweed, perennial ragweed, western ragweed

French: herbe à poux vivace

Habit:  herb

Description:  "Perennials,10-60 (-100+) cm. Stems erect. Leaves proximally opposite, distally alternate; petioles 0-25 mm (often ± winged); blades deltate to lanceolate, 20-60 (-140) x 8-35 (-50+) mm, pinnately toothed to 1-pinnately lobed, bases cuneate to truncate, ultimate margins entire or toothed, abaxial and adaxial faces hirsutulous to strigose and gland-dotted. Pistillate heads clustered, proximal to staminates; florets 1. Staminate heads: peduncles 0.5-2 mm; involucres obliquely cup-shaped, 2-4 (-5) mm in diameter, hirsutulous; florets 5-15 (-30+). Burs: bodies ± obpyramidal to globose, 2-3 mm, hirsutulous, spines or tubercles 0 or 1-6, mostly distal, stoutly conic to acerose, (0.1-) 0.5-1 mm, tips straight"  (Flora of North America online).

Known to hybridize with Ambrosia artemisiifolia.

Habitat/ecology:  "Disturbed sites, often wet, alkaline, clay soils; 0-2200 m"  (Flora of North America online).

Propagation:  Seed

Native range:  North America (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
New Caledonia New Caledonia Archipelago	Île Grande Terre	introduced invasive	MacKee, H. S. (1994) (p. 31) Voucher cited: MacKee 20601 Spontané

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	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
Australia Australia (continental)	Australia (continental)	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) South Australia, Victoria Naturalized
Australia Australia (continental)	Queensland	introduced invasive	U.S. Dept. Agr., Agr. Res. Serv. (2013) Naturalized
British Columbia (province of Canada) Province of British Columbia	Canada (British Columbia)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Japan Japan	Japan	introduced	Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 189)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
Taiwan Taiwan Island	Taiwan Island	introduced	Ching-I Peng, ed. (2013)
United States (west coast) United States (west coast states)	USA (Oregon)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (west coast) United States (west coast states)	USA (California)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)
United States (west coast) United States (west coast states)	USA (Washington)	native	U.S. Dept. Agr., Agr. Res. Serv. (2013)

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:  If you know of control methods for Ambrosia psilostachya, please let us know.