European Buckthorn from the area.
We were fortunate to have a few 'patches' of significant natives when we bought our house, one being underneath some large oak trees where there is a good quantity of Bloodroot and Virginia Waterleaf and this other area with the Nodding Trilliums, Wild Leeks, Red and White Baneberry, and Fern species.
Ant Dispersed Seeds talked about how Wild Ginger and Bloodroot seeds are dispersed by ants. Trilliums also fall in to that category having the same fleshy elaiosome that ants think are tasty caterpillars. They carry the seeds off to their nest, eat the elaiosome and dispose of the seed in their 'trash'.
Nodding trillium is different from many other trilliums because as the common name suggests, the white flower hangs downward underneath the three leaves.
Nodding Trillium is native to northeastern North America. See map.