Trillium undulatum f. enotatum photographed by Jim McClements near the Blue Ridge Parkway in North Carolina.
COMMENT BY Mike Slater:
There were a few typical Trillium undulatum plants in this population with nearly unmarked flowers so comparisons could be easily made. After much close examination of the plants, Jim and Carl Denton convinced me that these were a form of T. undulatum. In all aspects except the flowers the two forms appeared identical and they were growing together in very acid soil in deep shade.
But in addition to the almost complete lack of red markings on the petals, the petals were quite noticeably different in shape, as you can see in these two photos. The petals of typical T. undulatum are quite long and tapering with "undulating" margins, while the f. enotatum specimens we found had shorter petals which tapered abruptly short pointed little tip (apiculate) and the margins are straight. Therefore I wouldn't consider these plants to be simply a "white flowered form" of T. undulatum but a morphological form as well.