Carduus tenuiflorus may exceed 2 metres (6.6 ft) in height. Its tall stem is ridged with wings and has long spines which may be several centimeters in length. The dull olive-green leaves are lobed and wrinkled and may fold and crease themselves.
The inflorescences may hold up to 20 flower heads which are somewhat rounded, covered in wide, spiny phyllaries, and packed with pale pink to bright purple long-tubed disc florets. This is a tenacious weed of roadsides, fields, and disturbed areas.