Page author: Don Knoke
Silybum marianum
milk thistle
WTU specimens
Other herbaria

Distribution: Introduced weed now well established in California; occasional at scattered locations in the Pacific Northwest.

Habitat: Waste places.

Flowers: May - July

Origin: Introduced from the Mediterranean region

Conservation Status: Not of concern


Glabrous, herbaceous winter annual or biennial, spiny throughout, the stems 6-15 dm. tall.


Leaves pinnately lobed, up to 6 dm. long and 3 dm. wide, petiolate below, becoming sessile and clasping above, spiny margined, marked with white along the main veins.


Heads large, globose, terminating the branches; involucre bracts imbricate in several series, broad, firm, mostly spiny-margined and strongly spine-tipped, the coarse, spreading tips widened at the base; flowers all tubular and perfect; corollas purple, with slender tube and 5 long, narrow lobes; filaments glabrous, united at the base; receptacle flat, densely bristly; pappus of numerous, slender, unequal bristles.


Achenes flattened, glabrous, about 6 mm. long.

Accepted Name:
Silybum marianum (L.) Gaertn.
Publication: Fruct. Sem. Pl. 2: 378. 1791. 1791.

Synonyms & Misapplications:
(none provided)
Additional Resources:

PNW Herbaria: Specimen records of Silybum marianum in the Consortium of Pacific Northwest Herbaria database.

WA Flora Checklist: Silybum marianum checklist entry.

E-Flora BC: Silybum marianum atlas page.

CalPhotos: Silybum marianum photos.

USDA Plants: Silybum marianum information.

20 photographs:
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