Eastern Forest Threat Center - Scotch Thistle

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Scotch thistle stems and flowers

Scotch thistle stems and flowers

Steve Dewey, Utah State University, Bugwood.org

Scotch Thistle
Onopordum acanthium

Scotch thistle is native to Europe and eastern Asia. It was introduced into the U.S. as an ornamental in the 1800s.

Keywords: Asteraceae, herbaceous, biennial, annual, stout taproots, spines; Common names: cotton thistle, Scots cottonthistle, heraldic thistle, woolly thistle

Distribution Map Distribution Source Image

Threat Description

Scotch thistle is an herbaceous biennial (or sometimes annual) growing 6 to 8 ft. in height with stout taproots. The plant is coarse, many-spined, highly branched, grey-green in appearance, and is distinguished from all other thistles by a very dense, white woolly covering on its stems and leaves. Leaves are oblong, prickly, and toothed or slightly lobed along the margins. In the first year, leaves form a rosette. During the second year, cottony leaves are large (1 ft.), and hairy with triangular lobes. Dark pink to lavender flower heads measuring 1-2 in. in diameter stand alone on branch tips and bloom July to October. The whorl of bracts beneath the flower is tipped with flat, pale, orange-colored spines. Each plant can produce over 20,000 lightweight plumed seeds that are dispersed by wind, water, or by becoming attached to livestock. Scotch thistle thrives in light, well drained, sandy or stony soils. It occurs in waste places, dry pastures, fields, rangeland, and fence lines; along railroads and highways; and around old buildings. It is also found along rivers, streams, canals, or other waterways. It can form dense stands where it competes with native plants for resources.