Cirsium undulatum
Wavyleaf thistle
(c) Matt Lavin, some rights reserved (CC BY-SA) · licence
Family: Asteraceae · Type: Herb · Native
Cirsium undulatum (Wavyleaf thistle) is a native California herb in the Asteraceae family, recognized by runner roots, yellow spines, and large flowers diagnostic.
Wavyleaf thistle is a California native perennial found in the Modoc Plateau in disturbed areas, dry grasslands, and open scrublands at elevations below 1,600 meters. Flowering from May to October, this thistle produces white to pale lavender or pink flowers in heads 2.5 to 4.5 centimeters wide, arranged in flat-topped clusters. Growing 20 to 230 centimeters tall with white-tomentose stems that are generally simple at the base and few-branched toward the top, it emerges from runner roots. Its leaves are distinctively gray-tomentose on the upper surface and white-gray-tomentose underneath, with lower leaves 15 to 30 centimeters long, elliptic to oblanceolate, and shallowly lobed with spiny margins. The plant's phyllaries have distinctive spreading to reflexed tip-spines 2 to 5 millimeters long, with a sticky-resinous ridge along the midrib.
Identification and appearance
Key characters: 14 sympatric species; runner roots, yellow spines, and large flowers diagnostic
Habitat and range
Habitat: Disturbed areas, dry grassland, open scrubland
Elevation: < 1600 m
Outside California: to southern Canada, central United States
Bloom period
Cirsium undulatum blooms May-Oct.
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 undulatum native to California?
Yes. Cirsium undulatum is native to California (recorded as native).
When does Cirsium undulatum bloom?
Cirsium undulatum blooms May-Oct.
What plant family does Cirsium undulatum belong to?
Cirsium undulatum is in the Asteraceae family, genus Cirsium.
What habitat does Cirsium undulatum grow in?
Cirsium undulatum grows in Disturbed areas, dry grassland, open scrubland.
Related species
Other California species in the same genus, family, or bioregion.
- Cirsium vulgare — Bull thistle
- Cirsium andersonii — Anderson's thistle
- Cirsium andrewsii — Franciscan thistle
- Cirsium arizonicum — Arizona thistle
- Cirsium arizonicum var. arizonicum — Arizona thistle
- Cirsium arizonicum var. tenuisectum — Desert mountain thistle
- Cleomella arborea var. globosa — Bladderpod
- Constancea nevinii — Nevin's woolly sunflower
- Constancea sp.
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.