This plant seems to have been intentionally planted in the garden of the house we purchased. It spreads like wildfire - by thin roots it seems, and infiltrates even thick plantings of perennials.

I can never get rid of it because the roots are grown through those of other plants - the stem is almost succulent - seemingly fragile - but I'm lucky if I can find the bottom of a group of them to pull several out at a time.

The most I can to is pull out as much as possible piecemeal to hold back its advance.