Bull thistle is a biennial with a short, fleshy taproot that spreads by wind-dispersed seeds. The plant grows anywhere from 2-5 feet high. The flowers are pinkish-purple and appear on terminal stems; they also have narrow, spine-tipped bracts on their flowers. The leaves are dark green, rough, pinnately divided, and have long spines.
Bull thistle has a long history of being a weed in the United States and is found in every state including Hawaii. In Teton County, we often see bull thistle invading riparian areas that have high levels of moisture.
For advice on controlling this invader or for a free consultation of your Teton County residence, please contact Teton County Weed & Pest District at 733-8419.