We are working in a yard where this plant has taken over the flower beds. It was initially planted intentionally, but it has spread EVERYWHERE. My boss doesn't know what it is, and I can't find it in any of my books.

It is about 12-15" tall, with heart shaped grayish-green leaves. I don't think it flowers. It is growing in full sun. It grows on upright stems, and spreads with sturdy white roots underground. The roots are really hard to pull, so we have ended up snapping most of the stems off at the base. When pulled, it has a vaguely unpleasant odor which I can't describe. It is growing in huge clumps, and the ones around the edges fall forward so it has a mounded appearance.

I wish I had thought to take a picture, I'll try to remember if we go back tomorrow.

Thanks!