Cirsium rhothophilum
Surf thistle
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Family: Asteraceae · Type: Herb · Native
Conservation status: CNPS 1B.2
Cirsium rhothophilum (Surf thistle) is a native California herb in the Asteraceae family, recognized by coastal habitat, succulent texture, and pale flowers diagnostic.
Surf thistle is a rare (CNPS 1B.2) California native perennial found in southern coastal California in San Luis Obispo and northern Santa Barbara counties on coastal dunes and bluffs at elevations below 20 meters. Flowering from April to August, this plant produces white to pale yellow flowers in heads 3 to 4 centimeters wide, clustered closely among the plant's upper leaves. Growing with 1 to several stems 10 to 100 centimeters tall, it forms a distinctive bush-like or low mounded shape completely covered in dense gray felt-like hairs. Its strongly wavy leaves are densely gray or white-felted, with lower leaves up to 25 centimeters long, wing-petioled, and having spines 1 to 4 millimeters long. The plant's upper leaves become progressively more lobed and spinier, creating a distinctive architectural form characteristic of coastal dune environments.
Identification and appearance
Key characters: 11 sympatric species; coastal habitat, succulent texture, and pale flowers diagnostic
Habitat and range
Habitat: Dunes, bluffs
Elevation: < 20 m
Bloom period
Cirsium rhothophilum blooms Apr-Aug.
Conservation status
CNPS 1B.2
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 rhothophilum native to California?
Yes. Cirsium rhothophilum is native to California (recorded as native).
When does Cirsium rhothophilum bloom?
Cirsium rhothophilum blooms Apr-Aug.
What plant family does Cirsium rhothophilum belong to?
Cirsium rhothophilum is in the Asteraceae family, genus Cirsium.
Is Cirsium rhothophilum rare or endangered?
Cirsium rhothophilum carries California Rare Plant Rank 1B.2, state rank S1.
What habitat does Cirsium rhothophilum grow in?
Cirsium rhothophilum grows in Dunes, bluffs.
Related species
Other California species in the same genus, family, or bioregion.
- Cirsium scariosum — Meadow thistle
- Cirsium scariosum var. americanum — Dinnerplate thistle
- Cirsium scariosum var. citrinum — Southern meadow thistle
- Cirsium scariosum var. congdonii — Rosette thistle
- Cirsium scariosum var. loncholepis — La graciosa thistle
- Cirsium scariosum var. robustum — Shasta valley thistle
Sources: Jepson eFlora · CNPS Rare Plant Inventory · Index of California Plant Names · CalPhotos · CDFW CNDDB
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.