Ambrosia artemisiifolia
Common ragweed, Common Ragweed
(c) F. D. Richards, some rights reserved (CC BY-SA) · licence
Family: Asteraceae · Type: Herb · Not Native
Ambrosia artemisiifolia (Common ragweed) is a non-native California herb in the Asteraceae family, recognized by vestigial spines on small burs.
Common ragweed is a naturalized annual found in the Klamath Ranges, northern California Rocky Forests, northern and central Sierra Nevada, Sacramento Valley, southern Coast Ranges, southern California Coast, and Peninsular Ranges in disturbed sites at elevations below 1,050 meters. Flowering from July to October, this plant produces small green flowers in raceme-like clusters with asymmetric heads. Growing with much-branched stems up to 70 centimeters tall that can be occasionally marked with red or black, it spreads widely in disturbed landscapes. Its leaves are deeply divided with 2 to 3 pinnate segments, widely ovate and measuring 3 to 12 centimeters long, covered in strigose and soft hairs. The fruit develops as a spiny green to brown bur 2 to 4 millimeters long, with 4 to 12 generally blunt spines arranged in a single whorl.
Identification and appearance
Key characters: 11 sympatric species; vestigial spines on small burs are diagnostic
Habitat and range
Habitat: Uncommon. Disturbed sites
Elevation: < 1050 m
Outside California: to Alaska, Canada, +- worldwide, native to eastern United States
Bloom period
Ambrosia artemisiifolia blooms Jul-Oct.
How to tell it apart
vs Artemisia: Ambrosia produces spiny burs as fruits; Artemisia has tiny dry fruits without spines and strongly aromatic foliage.; vs Atriplex: Ambrosia has flower heads in spikes producing spiny burs; Atriplex has inconspicuous flowers with papery bracts and scurfy gray foliage.; vs Baccharis: Ambrosia has both male and female flowers on the same plant; Baccharis has male and female flowers on separate plants.; vs Eriogonum: Ambrosia has greenish flower heads producing spiny burs; Eriogonum has showy clusters of white, pink, or yellow flowers with papery bracts.; vs Salvia: Ambrosia has inconspicuous greenish flowers in the Asteraceae; Salvia has showy tubular lipped flowers typical of mints.
Frequently asked questions
Is Ambrosia artemisiifolia native to California?
No. Ambrosia artemisiifolia is not native to California (recorded as not native).
When does Ambrosia artemisiifolia bloom?
Ambrosia artemisiifolia blooms Jul-Oct.
What plant family does Ambrosia artemisiifolia belong to?
Ambrosia artemisiifolia is in the Asteraceae family, genus Ambrosia.
What habitat does Ambrosia artemisiifolia grow in?
Ambrosia artemisiifolia grows in Uncommon. Disturbed sites.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.