Common Name: Bighead Knapweed
Scientific Name: Centaurea macrocephala
Habitat: ornamental beds, farmland, grassland
Provincial Designation: Prohibited Noxious
Prohibited Noxious weeds are plant species designated in the Alberta Weed Control Act. Prohibited noxious weeds must be destroyed, meaning all growing parts need to be killed or the plant's reproductive mechanisms need to be rendered non-viable.
Bighead knapweed is native to Eastern Europe and was introduced to North America as an ornamental garden plant. It is sold locally - please do not purchase!
It out-competes grasses and other forage species, reducing food sources for wildlife and livestock, and competing with native vegetation for nutrients and light. Washington state has been attempting to eradicate an infestation of 4 hectares for about 25 years.
Bighead knapweed has conspicuously large, yellow flowers that are 3-8 cm wide.
The leaves are large, broad, rough, hairy, and lance-shaped with pointed tips, alternating on the stem. The leaves grow pointing upwards and blades of the leaves extend down along the stem creating characteristic vertical “wings” on the stem.
This is the largest ‘thistle-like’ plant in Alberta, which makes it easier to identify. Bighead knapweed grows up to 150 cm tall, usually in a single stalk.
Can Be Confused With
Thistles and other knapweeds when not in bloom.
Bachelor’s Buttons - Centaurea montana - and related garden cultivars and hybrids which are ornamental garden plants and fine for you to grow!
Learn more about this species:
See Fact Sheet - Alberta Invasive Species Council