: Common thistle, Spear thistle
: This species is listed as a prohibited noxious weed by the Michigan Department of Agriculture.
: Biennial and sometimes annual or monocarpic perennial; Juvenile phase produce a single rosette with a taproot up to 28 in long, rosettes may develop up to 3.3 ft in diameter. Taproots do not spread but develops several smaller lateral roots.
: More or less lance-shaped and 3-12 in long, prickly hairy on the top and very hairy underneath. Lobes are tipped with stout spines.
: Upright, covered with spiny wings and grow 1-6.6 ft tall with many spreading branches, and sometimes a single stem.
: 1.5-2 in in diameter, 1-2 in long, usually solitary, and more or less clustered at the ends of shoots and branches, subtended by narrow, spine-tipped bracts; blooms June through October.
Fruit and seeds
: Fruits are achenes, 1/16 in long with a long, hairy plume that is easily detached.
: Native to Europe, western Asia and northern Africa. Found in pastures, overgrazed rangelands, recently burned forests, forest clear-cuts, and along roads, ditches, and fences.
: By seed. Bull thistle typically produces 100 to 300 seeds per flower and can have over 400 flowers per plant; may require cross-fertilization to produce fertile seed.
: Swamp Thistle (Cirsium muticum
), Field Thistle (Cirsium discolor
) do not have spiny, winged stems. European swamp thistle (Cirsium palustre
) has spiny winged stems but its flowers are much smaller at 1.5 cm (0.8 in) or less in diameter.
Monitoring and rapid response
: Mow to prevent seeding; effectively controlled using any of several readily available general use herbicides such as glyphosate, triclopyr, or dicamba; natural enemies include the seed-feeding fly, Urophora stylata Fabricius.
: The information provided in this factsheet was gathered from the U.S. Forest Service.
Individual species images that appear with a number in a black box are courtesy of the Bugwood.org network (http://www.invasive.org).Individual photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (http://images.google.com).