Ambrosia trifida

Ambrosia trifida_C022-07
Photo: UC Davis Weeds of California

Common names: giant ragweed

Ambrosia trifida (giant ragweed) is an annual herb (family Asteraceae) with a long cluster of green-yellow flowers and opposite leaves found in the central western and southwestern areas of California. Giant ragweed has both female and male flower parts. It is native to the central and eastern United States. It favors grasslands. It spreads via seeds, and easily re-sprouts after being cut.

Cal-IPC Rating: Watch

CDFA Rating: B*?


Plant Risk Assessment - An evaluation of the potential for a plant to be invasive in California.

Weed Management Notes

No Weed RIC Management Notes are available for this species. Check for information on other species in the genus on the Weed RIC site.

Cal-IPC Newsletter Articles

There are no newsletter articles associated with this species yet.

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

There are no Symposium presentations associated with this species yet.

Other Ambrosia trifida Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - Distribution map and records of this species in California.
  • CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
  • EDDMapS - Distribution of this species in North America.
  • Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.
  • Additional photos

    Ambrosia trifida_leaf, stem, male and female flowers_copyright_DeanKelch(CDFA)
    Ambrosia trifida (giant ragweed) leaf, stem, male and female flowers. Photo: &#169 Dean Kelch, CDFA
    Ambrosia trifida_inflorescence_RichardSpellenberg
    Ambrosia trifida (giant ragweed) inflorescence. Photo: Richard Spellenberg
    Ambrosia trifida_male flowers_RichardSpellenberg
    Ambrosia trifida (giant ragweed) male flowers. Photo: Richard Spellenberg