Carduus acanthoides, known as the spiny plumeless thistle, welted thistle, and plumeless thistle, is a biennial plant species of thistle in the Asteraceae-sunflower family. The plant is native to Europe and Asia.
The plant is native from France, Italy, and western Turkey; through Russia and Kazakhstan; to China. In its native range the plant is found in open grasslands and disturbed areas, and in non-native ranges it's a weed of annual grasslands, roadsides, fields and pastures, and disturbed areas.
Carduus acanthoides may exceed 2 metres (6.6 ft) in height and can form weedy monotypic stands. The stem and foliage are spiny and sometimes woolly. The plant starts from a flat basal rosette and then bolts an erect stem with occasional toothed, wrinkled, spiny leaves.
At the top of each branch of the stem is an inflorescence of one to several flower heads, each rounded, covered in spiny phyllaries, and bearing many threadlike purple disc florets. The achenes are 2-3 mm long, with faint lengthwise stripes. Pappus bristles are 11-13 mm long.
Carduus acanthoides is well known in many other parts of the world, including parts of North and South America, New Zealand, and Australia, as a noxious weed. It is an invasive species in many regions of Canada and the United States, including California and West Virginia. The California Department of Food and Agriculture has an active program to control known populations.