A few years ago, I bought one of these at a nursery: http://davesgarden.com/guides/pf/go/80953/ It's a California native, and I figured I had just the right spot for it in my Seattle back yard, in a bed on the east side of my house that gets morning sun and shade for the rest of the day. Well, it's very cool looking with crazy flowers that look like space-age Alliums... but it has now taken over the whole length of the yard. Turns out, it just spreads runners in semi-moist soil, and since its leaves (and those of the other plants around it -- including Ligularia, Rodgersia, Gunnera, Hosta, Spirea, ferns,etc.) keep the ground well-shaded even in the morning, it just keeps a-growin'. I think I've managed to get rid of it in one area, but only through an experimental use of Round-Up (which I don't like to use, but it's the only way to get all the 1/2-inch-thick runners, which form a dense network just an inch or two underground). I've taken to cutting off the leaves and using an eyedropper to squirt a little Round-Up down the hollow stems. So far, so good. We'll see how much comes back next spring. Root fragments tend to form whole new plants!