Eastern Forest Threat Center - Purple Star Thistle

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Purple star thistle flowers

Purple star thistle flowers

Steve Dewey, Utah State University, Bugwood.org

Purple Star Thistle
Centaurea calcitrapa

Purple starthistle is native to the Mediterranean region of southern Europe and northern Africa. It was first detected in the U.S. in the early 1900s.

Keywords: Asteraceae, biennial, cobwebby hairs, spiny flower bracts, prickles; Common names: red star thistle, St. Barnaby's thistle, golden starthistle

Distribution Map Distribution Source Image

Threat Description

Purple star thistle is a biennial that reproduces rapidly by seed. Its stems and leaves are covered with cobwebby hairs that are lost on the leaves of mature plants. The lower leaves are deeply divided, and upper leaves are narrow and undivided. Flower heads are ¾ to 1 in. long and lavender to deep purple. Flower bracts have rigid, straw-colored spines about 1 in. long, with 1 to 3 pairs of lateral prickles near their base. The plumeless seeds have no bristles and are straw-colored and mottled with dark brown. Purple star thistle infests rangeland, pastures, and roadsides and invades and displaces native vegetation. This plant is unpalatable, but may replace valuable forage species. It is very competitive and capable of adapting to diverse climatic and soil conditions.