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slender flowered thistle (Carduus tenuiflorus)
ODA rating: B
USDA symbol:  CATE2
Oregon slender flower thistle distribution
Other common names
Shore thistle

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Images courtesy of Eric Coombs, Oregon Dept. of Agriculture.
If images are downloaded and used from the ODA web site please be sure to credit the photographer.

Annual or sometimes biennial; blooms May to June. Grows 1 to 4 ft tall. Stems have spiny wings. Leaves deeply cut into 2 to 5 pairs of lobes and undersurface slightly woolly. Flowers purplish to pinkish, borne in cylindrical heads either solitary or in clusters of 2 to 5. Bracts hairy; fruits from outer part of flower head gray, inner portion are yellowish to tan. Nearly identical to Italian thistle, but has larger clusters of flower heads.

It infests roadsides and waste areas, and has become a major problem on hill pasture land in Douglas county, Oregon. Once established, it spreads rapidly and forms dense stands which displace more desirable vegetation and exclude livestock.
Slender-flowered thistle is native to southern Europe. Heavy infestation in southwestern Oregon and smaller infestation in northwestern counties in Oregon.
Distribution in Oregon
The first documented site in Oregon was 1939 in Coos County.

Biological controls
Two approved biocontrol agents, a seed head weevil and a stem-boring fly, have been successfully established in Oregon.
Cheilosia corydon
Rhinocyllus conicus
Trichosirocalus horridus