Deep (and even not so deep) in the Frederick City Watershed in Frederick, Md., the Japanese stiltgrass grows in thick, luscious bunches. To the untrained eye, it's pretty, with its leafy layers blanketing the forest and transforming the ground into something out of a Grimm fairytale. But to those who know plants, the stiltgrass, along with several other invasive species , is less of a...