Page author: David Giblin
Ambrosia acanthicarpa
flat spine bur-ragweed, annual bursage, bur ragweed

Distribution: Occurring east of the Cascades crest in Washington; Washington to California, east to the Great Plains.

Habitat: Sandy soils, dunes, and other well-drained soils in open areas at low to middle elevations, often locally common.

Flowers: July-October

Origin: Native

Growth Duration: Annual

Conservation Status: Not of concern

Pollination: Wind


Monoecious, branching annual, 1-8 dm. tall, coarsely rough-hairy.


Leaves mostly alternate, petiolate, bipinnatifid, the blade 2-8 cm. long.


Heads numerous in elongate, terminal racemes, sometimes chiefly staminate or chiefly pistillate; staminate heads 2-4 mm. wide, short-pedunculate, not subtended by leaves; pistillate involucres solitary or clustered in the upper leaf axils, the burs 5-10 mm. long, with several series of flattened, divergent spines



Accepted Name:
Ambrosia acanthicarpa Hook.
Publication: Fl. Bor.-Amer. 1: 309. 1833.

Synonyms & Misapplications:
Franseria acanthicarpa (Hook.) Coville
Additional Resources:

PNW Herbaria: Specimen records of Ambrosia acanthicarpa in the Consortium of Pacific Northwest Herbaria database

WA Flora Checklist: Ambrosia acanthicarpa checklist entry

OregonFlora: Ambrosia acanthicarpa information

E-Flora BC: Ambrosia acanthicarpa atlas page

CalPhotos: Ambrosia acanthicarpa photos

37 photographs:
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