Erigeron bonariensis
Flax-leaved horseweed
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Family: Asteraceae · Type: Herb · Not Native
Erigeron bonariensis (Flax-leaved horseweed) is a non-native California herb in the Asteraceae family, recognized by non-native with distinctive gray-hairy appearance and essentially rayless heads.
Flax-leaved horseweed is a naturalized annual herb found in northern California regions including the Central Valley, Coast Ranges, Sierra Nevada foothills, and desert mountains at elevations up to 1,300 meters. Flowering throughout the year, this plant produces white to green-white and purple flowers in small disciform heads arranged in raceme-like clusters. Growing with erect or ascending stems 10 to 100 centimeters tall, densely covered in gray hairs and becoming branched towards the top. Its leaves range from oblanceolate basal leaves up to 8 centimeters long and 25 millimeters wide to narrow linear distal leaves 1 to 5 centimeters long. The fruit is pale tan, with 15 to 25 cream-colored pappus bristles 3 to 4 millimeters long.
Identification and appearance
Key characters: 42 sympatric species; non-native with distinctive gray-hairy appearance and essentially rayless heads
Habitat and range
Habitat: Disturbed sites
Elevation: < 1300+ m
Outside California: to eastern North America, native to South America
Bloom period
Erigeron bonariensis blooms All year.
How to tell it apart
vs Bellis: Erigeron has double-layered pappus (outer scales + inner bristles); Bellis completely lacks pappus.; vs Symphyotrichum: Erigeron has double pappus (2 layers); Symphyotrichum has single layer of uniform bristles.; vs Corethrogyne: Erigeron has simple unbranched stems; Corethrogyne has branched stems.; vs Pseudognaphalium: Erigeron has flat button-like flower heads; Pseudognaphalium has woolly clustered heads without rays.; vs Artemisia: Erigeron has obvious ray petals around yellow disk; Artemisia lacks ray petals entirely.
Frequently asked questions
Is Erigeron bonariensis native to California?
No. Erigeron bonariensis is not native to California (recorded as not native).
When does Erigeron bonariensis bloom?
Erigeron bonariensis blooms All year.
What plant family does Erigeron bonariensis belong to?
Erigeron bonariensis is in the Asteraceae family, genus Erigeron.
What habitat does Erigeron bonariensis grow in?
Erigeron bonariensis grows in 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.