florida Early Detection Network


Scotch thistle


Onopordum acanthium L.


Aster family


Onopordum acanthium


Basal Rosettes


Flower Close-up

Spines on Leaves


Synonyms: None


Botanical Glossary

Onopordum acanthium is an herbaceous biennial that grows up to 2 m (6.5 ft.) in height or rarely taller. The plant is coarse, many-spined and is highly branched. The stems of Onopordum acanthium are winged. The whole plant is densely tomentose, giving it a bluish-white appearance. 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 30 cm (1 ft.) long. Since this plant is a biennial, only the basal rosette of leaves is present in the first year of its growth. The flower heads are purple and measure 2.5-5 cm (1-2 in.) in diameter. All of the bracts of the involucre are tipped with flat, pale, orange-colored spines. Onopordum acanthium flowers from July to October. The seeds of this plant are 4-5 mm (0.2 in.) long. They are gray in color, and attached to a brown-colored pappus that can be two times as long as the seed. Page References Bailey 1029, Fernald 1543, Gleason & Cronquist 614, Holmgren 584, Magee & Ahles 1022, Peterson & McKenny 302. See reference section below for full citations.


Other native and invasive thistles


The seeds of Onopordum acanthium are dispersed by wind and water, by means of its pappus.


Onopordum acanthium is native to west, central and southern Europe as well as some parts of Russia. In the United States the plant is found in most states, from Vermont to Virginia, Alabama and Florida and west to California, Oregon, and Washington. In New England this plant has been reported from Vermont, Massachusetts, Connecticut and Rhode Island.


Though the actual date of introduction of Onopordum acanthium is unknown, it was most likely introduced in the 19th century as a garden plant. Since it is easily dispersed via wind and water, it likely escaped from gardens onto the landscape.


Abandoned Field, Agricultural Field, Edge, Open Disturbed Area, Pasture, Roadside, Vacant Lot, Yard or Garden. Onopordum acanthium can still be found in gardens in New England. However, it is more common in agricultural settings, where it is the most problematic.


Onopordum acanthium is a major agricultural weed in the western United States. If the soil is moist enough, it has the ability to resprout when its roots are cut up during cultivation. This plant spreads easily because each plant can produce over 20,000 lightweight seeds that are dispersed by wind as well as water. The seeds can also be dispersed by becoming attached to livestock. Onopordum acanthium should be monitored in New England in order to avoid it becoming as problematic as it is in many western states.


Washington State Noxious Weed Control Board


Documentation required: A specific photograph or mounted snippet of the flowers, leaves, and/or rosettes. Best time for documentation: Spring, summer, fall.


Integrated Taxonomic Information System Taxonomic information

PLANTS Database General information and map

Global Invasive Species Database Images, description, and general information

Washington State Noxious Weed Control Board Fact sheet with description and photographs

Field Guide to Noxious and Other Selected Weeds of British Columbia Images and description


Bailey, L. H. 1949. Manual of Cultivated Plants. Macmillan, New York.

Britton, N. L. and A. Brown. 1970. An Illustrated Flora of the Northeastern United States vol. 3. Dover Publications Inc., New York.

Fernald, M.L. 1950. Gray's Manual of Botany 8th ed. American Book Co., Boston.

Gleason H.A. and A.C. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed. New York Botanical Garden, Bronx, New York.

Holm, L.G., J.V. Pancho, J.P. Herberger, D.L. Plucknett, D.L. 1979. A Geographical Atlas of World Weeds. John Wiley and Sons, New York, USA.

Holmgren N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual. New York Botanical Garden, Bronx, New York.

Magee D.W and H.E. Ahles. 1999. Flora of the Northeast. University of Massachusetts Press, Amherst.

Peterson R.T. and M. McKenny. 1968. A field Guide to Wildflowers of Northeastern and North-central North America. Houghton Mifflin, Boston.

Qaderi, M.M. and P.B. Cavers. 2000. Variation in germination response within Scotch thistle, Onopordum acanthium L., populations matured under greenhouse and field conditions. Ecoscience 7 (1): 57-65.

Qaderi, M.M. and P.B. Cavers. 2000. Variation in germination response among local populations of Scotch thistle, Onopordum acanthium L. Seed Science and Technology 28 (3): 881-886.

Qaderi, M.M. and P.B. Cavers. 2000. Interpopulation variation in germination responses of Scotch thistle, Onopordum acanthium L., to various concentrations of GA(3), KNO3, and nahco3. Canadian Journal of Botany-Revue Canadienne De Botanique 78 (9): 1156-1163.

Stubbendieck, J., G.Y. Friisoe, M.R. Bolick. 1994. Weeds of Nebraska and the Great Plains. Nebraska Department of Agriculture, Bureau of Plant Industry. Lincoln, Nebraska. 589 pp.

USDA, NRCS. 2001. The PLANTS Database, Version 3.1. (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Whitson, T.D. (ed), L.C. Burril, S.A. Dewey, D.W. Cudney, B.E. Nelson, D.L. Richard, R.P. Parker. 1996. Weeds of the West. The Western Society of Weed Science, Newark.