Ambrosia trifida
giant ragweed
WTU specimens
Other herbaria

Distribution: Native and widespread in central and eastern United States; an occasional introduction in the Pacific Northwest.

Habitat: Waste places, usually in moist soil.

Flowers: July-October

Origin: Introduced

Conservation Status: Not of concern

Description:
General:

Monoecious, coarse annual from a few decimeters to several meters tall with short, stiff hairs above.

Leaves:

Leaves opposite, petiolate, ovate or sub-orbicular, serrate, palmately 3- to 5-lobed, or without lobes in small plants, the blade 2 dm. long or more, rough on both sides.

Flowers:

Staminate heads small, numerous, short-pedunculate, in an elongate, bractless, spike-like inflorescence, the involucres 3-nerved; pistillate heads borne below, in the leaf axils, the involucres 5-10 mm. long in fruit, several-ribbed, each bearing a short spine at the summit.

Accepted Name:
Ambrosia trifida L.
Publication: Sp. Pl. 2: 987. 1753. 1753.

Synonyms & Misapplications:
Ambrosia aptera DC.
Ambrosia trifida L. var. integrifolia (Muhl. ex Willd.) Torr. & A. Gray
Ambrosia trifida L. var. texana Scheele
Ambrosia trifida L. var. trifida [HC]
Additional Resources:

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

WA Flora Checklist: Ambrosia trifida checklist entry.

E-Flora BC: Ambrosia trifida atlas page.

CalPhotos: Ambrosia trifida photos.

USDA Plants: Ambrosia trifida information.

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