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: 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	Ching-I Peng, ed. (2011)
Canada Province of British Columbia	Canada (British Columbia)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Canada Canada	Canada (country)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Japan Japan	Japan (country)	introduced	Mito, Toshikazu/Uesugi, Tetsuro (2004) (p. 189)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Taiwan Taiwan	Taiwan Island	introduced	Ching-I Peng, ed. (2011)
United States (west coast) United States (west coast states)	USA (Oregon)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
United States (west coast) United States (west coast states)	USA (California)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
United States (west coast) United States (west coast states)	USA (Washington)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

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)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
United States (continental except west coast) United States (other states)	USA (Florida)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

Additional information:
Fact sheet from USDA Forest Service Fire Effects Information System (FEIS).
Fact sheet from the Australian National Weeds Strategy.
Impact assessment from Victoria, Australia.

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

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

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

References:

Ching-I Peng, ed. 2011. Digital flora of Taiwan (online resource).

Flora of North America Editorial Committee, eds. 2011. Flora of North America North of Mexico (online edition).

MacKee, H. S. 1994. Catalogue des plantes introduites et cultivées en Nouvelle-Calédonie. Muséum National d'Histoire Naturelle, Paris, 164 p.

Mito, Toshikazu/Uesugi, Tetsuro. 2004. Invasive alien species in Japan: the status quo and the new regulation for prevention of their adverse effects. Global Environmental Research 8(2)/2004: 171-191.

U. S. Government. 2011. Integrated Taxonomic Information System (ITIS) (on-line resource).

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.