Onopordum acanthium (Scotch Thistle)

Plant Info
Also known as: Scotch Cotton-thistle
Family:Asteraceae (Aster)
Life cycle:biennial
  • Weedy
Habitat:sun; disturbed soil, fields, roadsides, waste areas
Bloom season:June - September
Plant height:3 to 9 feet
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: round

[photo of flowers] Typical thistle reddish purple to pink, occasionally white. Flower receptacle however is broad and flatter than most thistles, fleshy and covered with spreading, thick, spiny bracts. The 1½ to 2 inch flower heads can be solitary or in clusters up to five at the ends of branching stems.

Leaves and stem: Leaf attachment: alternate Leaf type: lobed Leaf type: simple

[photo of leaves] Entire plant is covered with a velvety white bloom. Leaves are alternate, coarsely lobed or toothed with somewhat wavy edges, spiny, broad and up to 12'' long at base of the plant. Stems are much branched and guarded by broad spiny winged extentions of the leaf base that extends to the next leaf node below it. Stems have a sturdy taproot


This is Minnesota's newest and least distributed alien purple flowered thistle species. While sightings are being made at locations more southerly (this is likely moving up from south western populations from South Dakota, Kansas and Nebraska) it is not common here (yet). Reports of invasiveness include range/pasture land stands that cattle cannot penetrate. Some question its hardiness this far north but likely it will adapt just fine. At the site where these photos were taken, new construction has destroyed all traces of these plants, though the seed bank can potentially escape on construction equipment. While the bracts of Scotch Thistle may resemble those of Bull Thistle (Cirsium vulgare) or Plumeless Thistle (Carduus acanthoides), the silvery green leaves and stem make this one easy to distinguish.

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More photos

Photos by Peter M. Dziuk, taken across University Avenue behind Regions Hospital in dowtown St. Paul


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Samuel - Battle Creek Park, Ramsey county
on: 2013-07-14 11:13:35

Quite prolific breeders.

Posted by: K. Chayka
on: 2013-07-18 11:13:56

Samuel, Battle Creek Park has a fairly large amount of Carduus nutans, nodding thistle, and is probably what you saw instead. It has broad, showy bracts and more deeply lobed, hairless green leaves, where Scotch thistle has narrow, sharply pointed bracts and is a silvery green color all over.

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