Calystegia sepium

Invasive but with many medical uses.This relative of the morning glory creeps through the concrete and dilapidation of town back from a time when Natives used it to treat spider bites. Believed to have antibacterial and antifungal properties, hard to believe it's now considered a nuisance...

@columbiariver I see! I've only dealt with it on other people's properties. So it's yet to attack me. A neighbor when I was a kid, had morning glories, and I can recall my father's frustrations for these guys choking everything out. But as far as the worst plant... ever accidently stumble on bull thistle? it's like a grenade when you hit it with a weedwhacker..