An erect, spiny perennial in the Aster family, one to five feet tall, with spreading fleshy roots that produce shoots, thus forming spreading colonies. As the plant matures it elongates and leaves develop irregular indentations with prominently spiny margins. Stems are grooved and branch only at the top of the plant. Canada thistle flowers throughout the summer. Seeds are enclosed in a dandelion-like head of feathery bristles.
Fleshy roots are thick and up to a three-feet deep.
Plants die back with a hard frost, but dead stems and prickly leaves may persist. It is increasingly common in western North Carolina. Plants tolerate a wide range of soil types and cropping systems but tend to be more common in perennial crops and under reduced tillage systems. Plants are spread by cultivation and transportation of broken root pieces. Long distance transport has been documented in contaminated hay.