Spotted knapweed is a short-lived, tap rooted perennial that reproduces by seed.
One of the identifying characteristics is the pronounced black tip on the bracts of the seed head. The ends of these bracts have a spine that is moderately stiff, but not nearly as much as the spine on the diffuse knapweed. The knapweeds have shown that they may be alleopathic - they produce their own herbicide to reduce the vegetative growht of other plants. This results in a monoculture of knapweeds eventually. Knapweeds also are poisonous to horses causing chewing disease of which there is no cure.