I would be grateful if anyone could identify this, what I think is a weed - it has a mass of top layer roots and then sends out one long root that goes for miles. If I leave it to flower it produces a single stem with a pink 4-5cm bottle brush type head. It's taken over my rockery, marched right across the other side of the garden trying to overgrow my heuchera bed. In one hour I removed three bucket loads of leaves and roots. Every spring I spend hours uprooting the thing.