Epilobium lactiflorum; the milky willowherb differs from all other willowherb species on Iceland in the white flowers instead of purple/mauve flower colors. Except for some desert highland regions and southern coastal regions this species grows almost everywhere on Iceland. From what I have seen the distribution of this species in all regions seems to be quite sparse.
It is a member of the Willowherb family (Onagraceae). The Icelandic name of this species is Ljósadúnurt.