"The nearly muticous involucred, the deep purple flowers, and the leaves bare and green above, principally distinguish this from some forms of C. undulatum, which moreover grows in high and dry ground (Gray 1853)." Flowers deep purple (Kearney & Peebles 1951). Phyllary edges have double rows of serratations, the anther tips are long attenuate (observed from isotype). "The scabrous-ciliolate edges of the principle involucral bracts give a good diagnostic character (Gray 1883)."