ant haven

I was happily focussing on this flower when I realised there were little ants crawling all over it!. I can't remember what this flower is called - the flower itself is just at the top of the plant, which I liked when I first bought it, then realised that it quietly burrows under the soil and throws up new shoots where you don't want them. I removed a lot of them this year but left a couple in as they add a nice dimension to the back border, being about 2 feet tall. If someone knows what it's called I would like to know, thanks.