Not a very exotic plant but it has suddenly shot up in the garden next to our pond - semi-shady and quite damp clay soil. It is getting on for 2 metres tall with frothy white flowers. Any help gratefully received - may have planted it sometime in the past but it has certainly kept itself hidden (until now) if I did.
It is goatsbeard, Aruncus dioicus
Update 2jul14: please see post following for Liz's correct ID.