The RHS Encyclopedia says this plant is clump-forming and non-invasive. I say wrong and wrong again, but I love it just the same. It doesn’t take over in no time, but it’s definitely spreading, and filling up a large area of the shade garden. I haven’t touched it. The Plant Bible also says it flowers from late spring to summer… wrong yet again. Well, maybe in the UK, but not here.
I got this plant in the woods up in the hills above Padova, (i Colli Euganei) the same day I dug up a bunch of wild garlic (Allium ursinum). Double score. Free, gorgeous invasive plants!