Onopordum acanthium (Scotch Thistle): Minnesota Wildflowers

Onopordum acanthium (Scotch Thistle)

Plant Info
Also known as:	Scotch Cotton-thistle
Genus:	Onopordum
Family:	Asteraceae (Aster)
Life cycle:	biennial
Origin:	Eurasia
Status:	Invasive - ERADICATE!
Habitat:	sun; disturbed soil, fields, roadsides, waste areas
Bloom season:	June - September
Plant height:	3 to 9 feet
USDA PLANTS database:	Minnesota county distribution map

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Detailed Information

Flower:

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.

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

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 (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.

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More photos

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

Comments

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