The Twin Cities falls within the eastern broadleaf forest biome dominated by hardwood trees such as ash, oak, and maple. However, at one time, this area was dominated by prairie and savanna ecosystems and careful observers can still spot grasses, sedges, and flowers that hint at those original plant communities. Wetland plant species still tend to dominate marshy areas. And, of course, there are plants rooted in soils underlying more permanent water bodies, such as the Mississippi and Minnesota Rivers and the lakes and ponds of the river floodplains. There are also invasive and exotic plant species that threaten those remaining pockets of natural plant communities.