Scotch thistle, Onopordum acanthium (Aster family) RN 32

Scotch thistle, Onopordum acanthium, a non-native plant was introduced into the United States during the late 1800's and has spread into all western states.
Highly disturbed sites where moisture is plentiful are prime habitat for Scotch Thistle. Roadside rights-of-way that are disturbed by road construction and maintenance are good examples of land where Scotch Thistle infestations occur. Due to its moisture cool weather requirements, most Arizona Scotch Thistle populations are found at elevations of 4500 to 8000 feet.
This species can become 5 to 6 feet tall with basal (rosette) leaves over 1 foot long. Scotch thistle typically germinates in late fall or late winter and flowers in May or June, then it dies during early summer.
Photographed by Jim Morgan near Watson Lake in Prescott Arizona on 8/20/06. My thanks to Dr. Francis E. Northam, University of Arizona, for species identification and technical and historical information.