This name is a synonym of Carduus occidentalis Nutt..
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record F40898C8-1FD1-4D3B-85E1-18DEEA3D428A).
This name record (from TICA) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Carduus occidentalis in version 1 of The Plant List.