Family: Asteraceae
Carduus image
Robert Bierman  
1a. Phyllaries mostly 2 mm wide or more; involucres 2.8-3 cm long, heads solitary,nodding...C. nutans – nodding thistle
1b. Phyllaries rarely as much as 2 mm wide; involucres 1.4-2 cm long, heads notnodding, clustered or solitary...C. acanthoides – plumeless thistle
2 species and one hybrid in WI; 5 in US & Canada; 90 worldwide.

Introduced from Eurasia and Africa.

Spiny-leaved herbs closely resembling Cirsium, but distinguished by the non-plumose, capillary pappus.

Johnson, M.E. and H.H. Iltis. 1963. Preliminary reports on the flora of Wisconsin: No. 48. Compositae Family. Wisconsin Academy of Sciences, Arts & Letters. 52:255-342.

Other Treatments:  

Flora of North America

Species within Polk County 2016