Description: This plant is a biennial forb. In the juvenile phase an individual can form a single rosette with a taproot up to 28 inches long. The rosettes can grow up to 3.3 feet in diameter. The leaves of bull thistle are lance-shaped and anywhere from 3-12 inches long. These leaves have prickly hairs on top and are very hairy on the underside. Flowers are usually solitary and clustered near the ends of shoots and branches, measuring 1-2 inches long. The fruits of bull thistle are achenes.
Ecological Threat: This plant has no nutritional value for livestock and competes with desirable forage. The sharp spines of this thistle deter livestock and wildlife alike, truly making it a pest.
Biology & Spread: Disturbed areas creative open habitats for seed production and seedling establishment of this invasive species.
Threat in Oklahoma: This invasive species is not suitable for consumption by livestock or wildlife and inhibits the growth of native flora.
Image Credit: Forest and Kim Starr, Starr Environmental, Bugwood.org - See more at: http://www.invasive.org/browse/detail.cfm?imgnum=5162039#sthash.EeSCBIzR.dpuf
Center for Aquatic and Invasive Plants