Common biennial – prefers a dry climate.
Similar growth habit and size to Scotch thistle. Has red-purple flowers a bit larger than Scotch thistle, and they droop long before maturity.
More difficult to control than Scotch thistle. Three insects have been introduced for biological control, one by feeding on the seed in the flower head, one that forms galls and a third that attacks
the rosettes. Herbicide-resistant ecotypes have developed in many parts of the country.