Hooker’s Thistle, a native species, has been added to the USWildflowers database (11/09/2012.) Scientific name is Cirsium hookerianum.  It  is also known by the common name White Thistle.  Photo below was taken in the Boise Foothills, Ada County, ID on June 21, 2011.   Go to the Hooker’s Thistle detail page for more photos and information.

Hooker’s Thistle, White Thistle – Cirsium hookerianum