Regional Noxious. Biennial or perennial.
Scotch thistle has woody, branched stems with long, spine-edged
wings running up the sides. It has numerous, large, bright violet to reddish
flowers supported by large spine-tipped bracts.
Woolly hairs cover large, irregularly-lobed
leaves that have sharp yellow spikes. Mature plants can be up to 3 m tall.
Scotch thistle can be competitive with desirable native forage
plants when it forms dense stands that are impenetrable to livestock.
This species can occasionally invade field crops.
In British Columbia, Scotch thistle is found at low elevations
along roadsides, irrigation ditches, on rangelands and disturbed areas.
The seeds contain a water-soluble germination inhibitor, so it is often
successful in moist areas such as riverbanks. It is regarded as a major
concern only in the North Okanagan region.
Scotch thistle spreads by seed, mainly on the wind, but also in
hay and water, and by attaching to clothing or animal fur.