Invasive Plants, Pacific Northwest
Spotted knapweed is a biennial to short lived perennial and considered regionally noxious under the BC Weed Control Act. Currently distributed throughout southern BC. It first appeared on Vancouver island in 1905 and has established itself quite well with many very large patches showing up on the North Island.
It has hairy, deeply cut leaves and purple flowers on one or more upright stems. The flower heads lower leaves have a black tipped fringe that gives a spotted appearance. Spotted knapweed has a large taproot and can grow to up to 1 meter in height.
It is a big seed producer, with some individual plants producing up to 140,000 seeds per square meter.
It prefers open areas and well drained soils. You can find it growing in grasslands, open forests, and along roadsides. It is intolerant to dense shade and prefers moist habitats.