- Carduus acanthoides is an annual or biennial herbaceous plant that grows to 5 ft. (1.5 m) tall.
- This thistle may exceed two meters in height and can form weedy monotypic stands. The stem and foliage are spiny and sometimes woolly.
- Flowering occurs from May to August. The flower heads are reddish-purple in color and up to 1 in. (2.5 cm) in diameter. Flower stems are branched with spiny wings extending to the flower heads.
- Seeds are oblong, striate, and slightly curved.
- Ecological Threat
- Carduus acanthoides infests open, disturbed areas such as pastures, roadsides, and railroad right-of-ways. It can form thick stands that reduce the forage potential of pastures and suppress the growth of desirable vegetation.
Colorado Department of Agriculture, Conservation Services Division 
Washington State Noxious Weed Control Board 
Colorado Weed Management Association 
Oregon Department of Agriculture 
Flora of China, www.eFloras.org 
California Invasive Plant Council 
USDA NRCS PLANTS 
USDA ARS GRIN 
Images from Bugwood.org