John, surely Oxalis pes-caprae doesn't strain your philosophy! I don't think this invader even expects a welcome itself, as it sneaks up on us so furtively, getting its foot in the door before we have a chance of slamming it in its face! (And so unfair on poor Bermuda for us to call this south African weed "Bermuda buttercup", as it doesn't come from there - the first time I ever saw it in the Mediterranean, years ago, the people I was with said it was called Bermuda clover, and that's what I've thought of it as ever since, as its leaves look so much more like clover than buttercup.)