Cirsium scariosum var. robustum
Shasta valley thistle, Shasta Valley Thistle
(c) Matt Lavin, some rights reserved (CC BY-SA) · licence
Family: Asteraceae · Type: Perennial · Native
Cirsium scariosum var. robustum (Shasta valley thistle) is a native California perennial in the Asteraceae family, recognized by branched stems with clustered heads distinguish from other varieties.
Shasta valley thistle is a California native perennial found in the Klamath Ranges and northwestern Modoc Plateau in wet ground, meadows, pastures, and marshes at elevations of 900 to 1,900 meters. Flowering from June to July, this plant produces white flowers in heads 2.5 to 4 centimeters wide, arranged in compact clusters. Growing with branched stems 25 to 70 centimeters tall, it develops a robust structure with stems that are generally branched throughout. Its leaves are distinctively textured, with upper surfaces jointed-hairy and lower surfaces densely covered in woolly tomentose, featuring phyllary tips with spines 1 to 6 millimeters long. The inner phyllary tips have expanded, scarious appendages with irregular teeth, giving the thistle a complex and intricate appearance.
Identification and appearance
Key characters: 17 sympatric species; branched stems with clustered heads distinguish from other varieties
Habitat and range
Habitat: Wet ground, meadows, pastures, marshes
Elevation: 900-1900 m
California counties: Siskiyou, Modoc
Outside California: Oregon
Bloom period
Cirsium scariosum var. robustum blooms Jun-Jul.
How to tell it apart
vs Carduus: Cirsium has fluffy, feathery seed tufts; Carduus has rough bristles or no pappus and continuous spiny wings down the stem.; vs Silybum: Cirsium leaves are plain green; Silybum has bright white marbling along the leaf veins.; vs Sonchus: Cirsium has thistle-type flowers with spine-tipped bracts; Sonchus has dandelion-like flowers and milky sap.; vs Cynara: Cirsium heads are 1-6 cm across; Cynara heads are massive (4-15 cm, tennis ball sized) with fleshy bases.; vs Centaurea: Cirsium has linear bracts without appendages; Centaurea bracts have fringed or comb-like tips.
Frequently asked questions
Is Cirsium scariosum var. robustum native to California?
Yes. Cirsium scariosum var. robustum is native to California (recorded as native).
When does Cirsium scariosum var. robustum bloom?
Cirsium scariosum var. robustum blooms Jun-Jul.
Where in California does Cirsium scariosum var. robustum grow?
Cirsium scariosum var. robustum occurs in Siskiyou, Modoc, at elevations of 900-1900 m.
What plant family does Cirsium scariosum var. robustum belong to?
Cirsium scariosum var. robustum is in the Asteraceae family, genus Cirsium.
What habitat does Cirsium scariosum var. robustum grow in?
Cirsium scariosum var. robustum grows in Wet ground, meadows, pastures, marshes.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-09-30
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.