Plants and animals introduced from another country or region are called exotic species. Because they are not native to their current area, they don't have natural enemies to control their population. And soon, these exotic species outcompete the native species for both food and space, reducing diversity. Ramsey County has produced a website that lists exotic/invasive plant species.  Some of these species have only recently been introduced and can still be controlled. Others have been growing in the area for some time. Below are several species present in Minnesota.