Idaho Trillium, a native species, has been added to the USWildflowers database (06/27/2011.)  Scientific name is Trillium petiolatum.   It is also known by the common names Long-petioled Trillium, Purple Trillium, Round Leaf Trillium, and Purple Wakerobin.  Photo below was taken in the Payette National Forest in Adams County, ID on June 18, 2011.  Go to the Idaho Trillium detail page  for more photos and information.

Idaho Trillium, Long-petioled Trillium, Purple Trillium, Round Leaf Trillium, Purple Wakerobin - Trillium petiolatum