Appearance: Biennial herbaceous plant, between 3 - 6' tall with one erect branched stem. It grows a rosette in its first year and blooms in its second year.
Leaves: Alternate, coarsely lobed, each lobe with a spine at its tip. Spines extend downward from the leaves along prominent ridges of the stem. Upper leaf surface is rough.
Flowers: Disk-shaped flowerheads contain hundreds of tiny individual purple flowers which bloom from July through August.
Seeds: Numerous straw-colored seeds with plume-like bristles are dispersed by wind. They remain viable in the soil for over 10 years.
Roots: Each plant has a fleshy taproot.
- US Forest Service Fact Sheet
- University of Minnesota Extension
- MISIN bull thistle identification training module