Scotch thistle USDA PLANTS Symbol: ONAC
U.S. Nativity: Exotic
Habit: Forbs/Herbs
Onopordum acanthium L.

Jump to: Resources | Images | Distribution Maps | Sources
Taxonomic Rank: Magnoliopsida: Asterales: Asteraceae
Synonym(s): Scottish thistle, cotton thistle, heraldic thistle, Scotch cottonthistle
Native Range: Europe to cent. Asia ()

Appearance
Onopordum acanthium is an herbaceous biennial plant that can grow up to about 6.5 ft. (2 m) in height. The plant is coarse, many-spined and is highly branched. The stems of O. acanthium are winged. The whole plant is densely tomentose, giving it a bluish-white appearance.
Foliage
The leaves are oblong and prickly, being toothed or slightly lobed along the margins. The apex of the leaf is acute. The leaves are mostly sessile, with some of the lower leaves having petioles. The blades of the lower leaves can measure up to 1 ft. (30 cm) long. Since this plant is a biennial, only the basal rosette of leaves is present in the first year of its growth.
Flowers
The flower heads are purple and measure 1-2 in. (2.5-5 cm) in diameter. All of the bracts of the involucre are tipped with flat, pale, orange-colored spines. Flowering occurs from July to October.
Fruit
The seeds of this plant are 0.2 in. (4-5 mm) long. They are gray in color, and attached to a brown-colored pappus that can be two times as long as the seed.
Ecological Threat
O. acanthium is a major agricultural weed in western United States. With enough moisture, it can resprout from roots cut up during cultivation. This plant spreads easily because each plant can produce over 20,000 wind dispersed seeds. The seeds can also be dispersed by water or by being caught in the fur of animals.

Identification, Biology, Control and Management Resources

Selected Images from Invasive.orgView All Images at Invasive.org


Plant(s);
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Plant(s);
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Flower(s);
Eric Coombs, Oregon Department of Agriculture, Bugwood.org
Additional Resolutions & Image Usage

Flower(s);
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Plant(s); in flower
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Feature(s); Flower and foliage
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Feature(s); Spines on Leaves
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Additional Resolutions & Image Usage

Plant(s);
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Plant(s); Rosette
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Flower(s);
Lesley Ingram, , Bugwood.org
Additional Resolutions & Image Usage

Foliage;
Bonnie Million, National Park Service, Bugwood.org
Additional Resolutions & Image Usage

Plant(s); Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 3: 556.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
Additional Resolutions & Image Usage

Fruit(s);
Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org
Additional Resolutions & Image Usage

Fruit(s); Young fruit with pappus and corolla remnant still attached. Note the reddish color of the bristles.
D. Walters and C. Southwick, USDA, Bugwood.org
Additional Resolutions & Image Usage

Plant(s);
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Infestation;
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Infestation;
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage

Infestation; on river bank, seeds travel down water way
Vince Belleci, , Bugwood.org
Additional Resolutions & Image Usage

EDDMapS Distribution:
This map is incomplete and is based only on current site and county level reports made by experts and records obtained from USDA Plants Database. For more information, visit www.eddmaps.org
 


State(s) Where Reported invasive.
Based on state level agency and organization lists of invasive plants from WeedUS database.

U.S. National Parks where reported invasive:
Grand Canyon National Park (Arizona)



Invasive Listing Sources:
California Invasive Plant Council
Faith Campbell, 1998
Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995.
Missouri Department of Conservation,
Pacific Northwest Exotic Pest Plant Council, 1998