Distribution: Occurring east of the Cascades crest in Washington; British Columbia to California, east across North America to the Atlantic Coast.
Habitat: Roadsides, fields, wastelots, and other disturbed open areas.
Flowers: July-October
Origin: Native
Growth Duration: Perennial
Conservation Status: Not of concern
Pollination: Wind
Monoecious perennial from creeping rhizomes, 1-10 dm. tall.
Leaves opposite below and alternate above, usually pinnatifid, lance-ovate or elliptic in outline, 3-10 cm. long, sub-sessile.
Staminate heads small, numerous, short-pedunculate, in an open inflorescence of several spike-like flowering shoots arising from the upper leaf axils; pistillate heads borne below, in the leaf axils; fruiting involucre a short-beaked bur, 3-5 mm. long, with a few rounded projections.
Achene
PNW Herbaria: Specimen records of Ambrosia psilostachya in the Consortium of Pacific Northwest Herbaria database
WA Flora Checklist: Ambrosia psilostachya checklist entry
OregonFlora: Ambrosia psilostachya information
E-Flora BC: Ambrosia psilostachya atlas page
CalPhotos: Ambrosia psilostachya photos