Cirsium douglasii
Swamp thistle, Swamp Thistle
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Family: Asteraceae · Type: Herb · Native
Cirsium douglasii (Swamp thistle) is a native California herb in the Asteraceae family.
Swamp thistle is a California native perennial herb found in wet meadows and riparian areas across the state's coastal and central regions. Flowering from June to September, this plant produces dark rose-purple (occasionally white) flowers in clustered heads 2 to 4.5 centimeters wide, with distinctive involucres featuring phyllaries tipped with dark purple patches and spreading spines. Growing 60 to 250 centimeters tall with multiple much-branched stems covered in gray, felt-like hairs, it develops a robust taproot or woody base. Its leaves are particularly notable, with basal leaves 30 to 110 centimeters long, featuring coarsely toothed or deeply lobed blades and spiny-toothed petioles, while cauline leaves have ear-like expanded bases with spiny wings. The plant's fruit is small, approximately 5 to 6 millimeters long, accompanied by a pappus 15 to 20 millimeters in length.
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 douglasii native to California?
Yes. Cirsium douglasii is native to California (recorded as native).
What plant family does Cirsium douglasii belong to?
Cirsium douglasii is in the Asteraceae family, genus Cirsium.
Related species
Other California species in the same genus, family, or bioregion.
- Cirsium douglasii var. breweri — Brewer's swamp thistle
- Cirsium douglasii var. douglasii — Douglas' swamp thistle
- Cirsium fontinale — Fountain thistle
- Cirsium fontinale var. campylon — Mount hamilton thistle
- Cirsium fontinale var. fontinale — Fountain thistle
- Cirsium fontinale var. obispoense — Chorro creek bog thistle
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.