Ageratina occidentalis
Western snakeroot, Western Snakeroot
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Family: Asteraceae · Type: Subshrub · Native
Ageratina occidentalis (Western snakeroot) is a native California subshrub in the Asteraceae family, recognized by differentiated by elevation range and leaf size.
Western snakeroot is a California native perennial herb or subshrub found in northwestern California, the high Cascade Range, Sierra Nevada, Warner Mountains, northern eastern Sierra Nevada, and White and Inyo Mountains on rocky sites in montane chaparral, conifer forest, and alpine areas below 3,700 meters elevation. Flowering from June to October, this plant produces white to purple flowers in heads 8 to 10 millimeters long arranged in clusters. Growing with erect or ascending green or purple stems 15 to 70 centimeters tall that are puberulent, it has a woody, somewhat rhizomatous caudex. Its proximal leaves are opposite while distal leaves are alternate, with blades 25 to 50 millimeters long, approximately triangular and somewhat serrate with glandular undersides. The fruit is 3 to 3.5 millimeters long.
Identification and appearance
Key characters: 1 sympatric species - differentiated by elevation range and leaf size
Habitat and range
Habitat: Rocky sites, montane chaparral, conifer forest, alpine
Elevation: < 3700 m
Outside California: to Washington, Idaho, Utah
Bloom period
Ageratina occidentalis blooms Jun-Oct.
How to tell it apart
vs Baccharis: Ageratina has opposite leaves and bisexual flowers; Baccharis has alternate leaves and separate male/female plants.; vs Spiraea: Ageratina has composite flower heads; Spiraea has individual 5-petaled flowers in branched clusters.; vs Venegasia: Ageratina has white rayless flowers; Venegasia has large yellow ray petals and huge triangular leaves.; vs Eupatorium: Same genus (Eupatorium is old name); plants are identical.; vs Scrophularia: Ageratina has composite flower heads; Scrophularia has tubular two-lipped flowers typical of figworts.
Frequently asked questions
Is Ageratina occidentalis native to California?
Yes. Ageratina occidentalis is native to California (recorded as native).
When does Ageratina occidentalis bloom?
Ageratina occidentalis blooms Jun-Oct.
What plant family does Ageratina occidentalis belong to?
Ageratina occidentalis is in the Asteraceae family, genus Ageratina.
What habitat does Ageratina occidentalis grow in?
Ageratina occidentalis grows in Rocky sites, montane chaparral, conifer forest, alpine.
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.