I have a lovely perennial that is disciduous, height 18-24", spreads by runners underground, and has light purple flowers in a 1" bell shape. I wouldn't call it invasive, but you have to keep at it or it will take over a large portion of the garden. It looks like a form of campanula but cannot find any pictures of the particular kind I have. The leaves are heart shaped and all up and down the stems. The flowers are all along the stems too. I purchased it from a greenhouse years ago when first establishing my perennial garden. CM
