- Centaurea jacea is a perennial plant that grows 1-4 ft. (0.3-1.2 m) tall. The stems are ridged and may have purple stripes.
- The basal leaves are oblanceolate to elliptic and 2-10 in. (5 -25 cm) long. Leaves become smaller as they ascend the stem. These smaller leaves are lanceolate and attach directly to the stem.
- The brown bracts of the inflorescence give this plant its common name. Flowering occurs from June to October, when rose to purple flowers appear in 1-1.25 in. (2.5-3.2 cm) wide, solitary heads at the tips of the branches.
- Centaurea jacea produces small light brown, plumeless seeds; about 12 per head.
- Ecological Threat
- Centaurea jacea is an aggressive invader preferring moister, cooler conditions than other knapweed species. It can tolerate partial shade. It can invade grasslands, open woods, meadows, pastures, woodland clearings, and cutover areas of forest crowding out native plants or forage. Centaurea jacea is native to Europe.
USDA Forest Service, Forest Health Staff, Newtown Square, PA Weed of the Week 
Washington State Noxious Weed Control Board 
University of California, Jepson Flora Project 
Flora of North America, www.eFloras.org 
California Invasive Plant Council 
USDA NRCS PLANTS 
USDA ARS GRIN 
Images from Bugwood.org