Scotch thistle is a member of the Aster family, Thistle tribe. It is a biennial that was introduced from Europe or eastern Asia and can reach a height of eight feet. Large, coarsely lobed, hairy leaves have a velvety-gray appearance. The rosette forms the first year and can have leaves up to two feet long and a foot wide.
The spiny-edged, alternate leaves form leaf wings that extend down onto the stem. This branching plant has reddish-purple to violet flowers and a large, fleshy taproot. Seeds are about 3/16 inch long and tipped with slender bristles.
It is found primarily along roadsides and railroads, but can become an impassible obstacle to livestock on range land and pastures. It is increasing in densities throughout Colorado.
In the Pueblo area a different species of Scotch thistle, Onopordumtauricum, is found. This species is bright green color and has no hair on the plant like the Oancanthium species. Scotch thistle has been sold in Arizona as a native xeric species.
Scotch thistle Info/Fact Sheet (PDF) Click Here
Dig up the Scotch rosettes before they get bigger and more widespread!