It's knot a weed!

I've had this little charmer for many years and can't remember where I got it from. My database would tell me in a second if I was on my work computer.

Polygonum runcinatum is a small perennial which grows about 15" tall. It's a bit of a spreader, but I wouldn't call it rampant - it's controllable. 

It's a fairly neat little plant and one which I would always like to have around - I might take a fragment with me when I retire! Shhh!