Page authors: Don Knoke, David Giblin
Silybum marianum
milk-thistle
WTU specimens
Other herbaria
WTU images

Distribution: Occurring in scattered locations on both sides of the Cascades crest in Washington; British Columbia to California, east across Canada and the southwestern U.S. to eastern North America.

Habitat: Roadsides, fields, wastelots, and other disturbed areas.

Flowers: May-July

Origin: Introduced from the Mediterranean region

Conservation Status: Not of concern

Description:
General:

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

Leaves:

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.

Flowers:

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.

Fruits:

Achenes flattened, glabrous, about 6 mm. long.

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