- Centaurea calcitrapa is a biennial to perennial plant. It grows 2-3 ft. (0.61-0.91 m) tall.
- The stems and leaves are covered with fine hairs. Lower and basal leaves are divided or deeply lobed. Leaves become less divided toward the apex of the plant.
- Flowering occurs from July to October, when purple to pink blooms develop at the ends of the stems. Floral bracts are tipped with 1 in. (2.5 cm) long, straw colored spines.
- The fruit is an achene 0.08-0.16 in. (2-4 mm) long which lacks a pappus.
- Ecological Threat
- A native of southern Europe, Centaurea calcitrapa produces prolific seeds and often invades floodplains, dry forests and grasslands.
Oregon Department of Agriculture Plant Programs, Noxious Weed Control 
Washington State Noxious Weed Control Board 
University of California, Jepson Flora Project 
Flora of North America, www.eFloras.org 
Nevada Department of Agriculture 
California Invasive Plant Council 
USDA NRCS PLANTS 
USDA ARS GRIN 
Images from Bugwood.org