Europe, western Asia, and northern Africa
Bull thistle is an upright forb that typically grows as a biennial but can also behave as an annual or very short-lived perennial. Plants are generally 3 ft (0.9 m) tall and have a long taproot. Leaves are 3–12 in (8–30 cm) long, lance-shaped, and lobed. They have coarse hairs and long, yellow, very sharp spines. Stems are stout and hairy with spiny wings. Flower heads have numerous purplish-pink florets as well as rows of narrow, spiny bracts tipped in white or yellow. The cream-colored seeds are streaked in brown and topped by a tuft of fine hairs.
Introduced thistles currently infest millions of acres across North America, primarily occurring in or along roadways, waterways, agricultural fields, rangelands, pastures, forests, and disturbed areas. They are responsible for millions of dollars of damage annually in reduced agricultural yields and lowered forage value in grazing systems. Introduced invasive thistles can also displace native vegetation, negatively impacting wildlife and threatening the delicate ecological balance within many habitats.
Randall, C.B., J.E. Andreas, and J. Milan. 2024. Introduced Thistles: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2024-8- INTRODUCED THISTLES-P. https://bugwoodcloud.org/resource/files/29168.pdf