Filipendula ulmaria; the meadowsweet grows on moist grounds favourable to plantgrowth. I photographed this plant in the eastern part of the Snæfellsness district at the edge of dense birch/rowan brush. It is easily recognizable because it is a rather large herb with inflorescense's of white flowers and pinnate-divided leaves. On the photo the flowers are still in bud and the inflorescence's not yet longitudinal stretched.
It is member of the rose family (Rosaceae). The Icelandic name of this species is Mjaðjurt.