Carduus acanthoides is an annual or biennial herbaceous plant that grows to 5 ft. (1.5 m) tall.
Foliage
This thistle may exceed two meters in height and can form weedy monotypic stands. The stem and foliage are spiny and sometimes woolly.
Flowers
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.
Fruit
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.