: Onopordum acanthium L. ssp. acanthium
: Scotch cotton thistle, cotton thistle, heraldic thistle
: Introduced to North America as an ornamental plant for its bold foliage and large flowers.
: Herbaceous biennial that grows up to 2 m (6.5 ft) in height, coarse, many-spined and highly branched. Stems are winged, densely tomentose, giving it a bluish-white appearance.
: Oblong and prickly, being toothed or slightly lobed along the margins. Apex of the leaf is acute, mostly sessile with some of the lower leaves having petioles. Blades of the lower leaves can measure up to 30 cm (1 ft) long, only basal rosette of leaves is present the first year of growth.
: Erect, branched, broadly spiny-winged, 2 m (6 ft) tall.
: Purple in color, 2.5-5 cm (1-2 in) in diameter, bracts of the involucre are tipped with flat, pale, orange colored spines; blooms from July to October.
Fruit and seeds
: 4-5 mm (0.2 in) long, gray in color, attached to a brown colored pappus that can be two times as long as the seed.
: Native to Eurasia. Found in waste places, dry pastures, fields, rangeland, fence lines, along railroads, highways and around old buildings.
: By seed.
: Native thistles such as marsh thistle (Cirsium muticum
) and exotic thistles such as Bull thistle (Cirsium vulgare
), European swamp thistle (Cirsium palustre
), and musk thistle (Carduus nutans
Monitoring and rapid response
: Small infestations should be physically removed by hand-pulling or cutting a few inches below soil surface. buried seed may persist for up to 20 years, therefore several years of re-treatment may be necessary; use Dicamba and 2,4-D herbicides; the thistle crown weevil (Trichosirocalus horridus
) feeds on musk, bull, plumeless, Italian and Canada thistles will also feed on Scotch thistle.
: 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).