Trillium cuneatum?

Can anyone share thoughts on the identification of this Trillium? I'm labeling photos from 2010 and not sure what it is. Trillium cuneatum seems likely, though it would be a significant range extension where it was found in southern Michigan. It seems possible that it was introduced at the site, a rich forest remnant where it was growing by the hundreds with several other Trillium species. Thanks for any help!