Ambrosia acanthicarpa
Annual bur-sage, Annual Bur-Sage
Photo by Chez Brungraber
Family: Asteraceae · Type: Herb · Native
Ambrosia acanthicarpa (Annual bur-sage) is a native California herb in the Asteraceae family, recognized by annual habit and straight-spined burs.
Annual bur-sage is a California native annual found in the North Coast Ranges, Sierra Nevada, San Joaquin Valley, Central Western California, southwestern deserts, Great Basin, and Mojave Desert in sandy plains and disturbed sites at elevations from 30 meters below sea level to 2,450 meters. Flowering from July to December, this plant produces pale yellow or greenish flower heads in small clusters, with distinctive staminate heads 2 to 5 millimeters in diameter. Growing with one to several ascending branches from a slender taproot, it reaches 40 to 150 centimeters tall and has a grayish, bristly appearance. Its lower leaves are opposite with large petioles 1 to 6 centimeters long, featuring deltate blades 1 to 8 centimeters wide that are shallowly lobed or pinnately divided. The fruit is a distinctive bur 5 to 7 millimeters long, golden or dark purple, with up to 30 sharp, spiraled spines that help with seed dispersal.
Identification and appearance
Key characters: 16 sympatric species; annual habit and straight-spined burs are diagnostic
Habitat and range
Habitat: Sandy plains, disturbed sites, many communities
Elevation: -30-2450 m
Outside California: to southern Canada, Michigan, Missouri, Texas, northwestern Mexico
Bloom period
Ambrosia acanthicarpa blooms Jul-Dec.
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 acanthicarpa native to California?
Yes. Ambrosia acanthicarpa is native to California (recorded as native).
When does Ambrosia acanthicarpa bloom?
Ambrosia acanthicarpa blooms Jul-Dec.
What plant family does Ambrosia acanthicarpa belong to?
Ambrosia acanthicarpa is in the Asteraceae family, genus Ambrosia.
What habitat does Ambrosia acanthicarpa grow in?
Ambrosia acanthicarpa grows in Sandy plains, disturbed sites, many communities.
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.