Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.
Microstegium vimineum, Japanese stiltgrass, is an annual grass native to Asia. The history of invasiveness for M. vimineum is classified as “High.” It was introduced into the United States in the early 1900’s as a packing material for porcelain in China and has since spread through natural dispersion from its initial introduction in Tennessee. M. vimineum spreads rapidly in disturbed areas and has a high potential to spread further throughout the eastern United States. The plant can form dense monocultures in forest understories, displacing native species and changing soil chemistry. Climate matching indicated the contiguous United States has a high climate match. The areas of highest climate match were concentrated where there are already established M. vimineum populations. The certainty of assessment is high. The overall risk assessment category is high.