Centaurea nigrescens (Tyrol knapweed, short-fringed knapweed or Tyrol thistle) is a perennial plant of the star thistle genus that grows natively in Central and South-eastern Europe (from Southern Germany and Northern Italy to Romania and Bulgaria), but has also been introduced and is now a noxious weed in the Northern United States, Canada and Southern Australia. It has purple flowers and it flowers in the summer (June to September). (Wikipedia)