Onopordum acanthium (Scotch Thistle)

Plant Info
Also known as: Scotch Cotton-thistle
Genus:Onopordum
Family:Asteraceae (Aster)
Life cycle:biennial
Origin:Eurasia
Status:
  • 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

Pick an image for a larger view. See the glossary for icon descriptions.

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

Notes:

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.

Please visit our sponsors

  • Minnesota Native Plant Society

Where to buy native seed and plants ↓

Map of native plant purveyors in the upper midwest

  • Natural Shore Technologies - Using science to improve land and water
  • Itasca Ladyslipper Farm - Native orchids, container grown
  • Prairie Restorations - Bringing people together with the land
  • Shop for native seeds and plants at PrairieMoon.com!
  • Shooting Star Native Seeds - Native Prairie Grass and Wildflower Seeds

More photos

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

Comments

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.

Post a comment

Note: All comments are moderated before posting to keep the riff-raff out. An email address is required, but will not be posted—it will only be used for information exchange between the 2 of us (if needed) and will never be given to a 3rd party without your express permission.

For info on subjects other than plant identification (gardening, invasive species control, edible plants, etc.), please check the links and invasive species pages for additional resources.



(required)




Note: Comments or information about plants outside of Minnesota and neighboring states may not be posted because Id like to keep the focus of this web site centered on Minnesota. Thanks for your understanding.