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Scotch Thistle (Onopordum acanthium)

Scotch thistle is a member of the Aster (sunflower) family, Thistle tribe. It is a biennial that was introduced from Europe or eastern Asia and can reach a height of 8 feet. Large, coarsely lobed, hairy leaves have a velvety-grey appearance. The rosette forms the first year and can have leaves up to 2 feet long and 1 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 impassable obstacle to livestock on rangeland and pastures. It is increasing in densities throughout Colorado.

In the Pueblo area a different species of Scotch thistle, Onopordum tauricum, is found. This species is bright green in color and has no hair on the plant like the 0. acanthium species. Both species are similar in management practices.

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