Onopordum acanthium (Scotch Thistle)
|Also known as:||Scotch Cotton-thistle|
|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):|
|National distribution (click map to enlarge):|
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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:
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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Photos courtesy 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?