Non-natives

I know that Rhododendron are a non-indigenous plants and that they spread like crazy. Also that they poison the ground beneath them against other plants, but when they are in bloom they can be lovely. The Stornoway Castle Grounds (surrounding our campus) were planted as a landscaped policy, with imported earth and lots of exotic trees and bushes. It is now a site of special scientific interest, and a wonderful recreational area. These things are all relative!