At the moment, I'm camping in the Great Basin surrounded by Bromus tectorum (cheatgrass) and whitetop (Cardaria pubescens). The cottonwoods, willows, and native grasses and forbs don't have a chance.
And I won't even begin to describe the destruction the salt cedar (Tamarix ramosissima) has wrought on the Southwest...
OTOH, let us not forget Kentucky bluegrass, which isn’t from KY at all. It’s from Europe.