Achillea ptarmica; the Sneezewort is a close relative of the Yarrow (A. millefolium) though both leaves and flowers are different. The leaves of the Sneezewort are long, very narrow with entire margins (finely toothed). Yarrow characteristically has leaves that are highly numerously incised - hence the name "millefolium" meaning thousand-leaf. The flower heads of the Sneezewort are larger and contain more single flowers than the Yarrow. Also the flower heads are not arranged in umbel-like inflorescences. Having said this though, when looking at the flower of the Sneezewort one immediately "senses" the close relationship of these two species.
The Sneezewort grows in rather wet conditions. It is not common, but sometimes found near human settlements. I took pictures of this plant in the wetland reserve near Eyrarbakki (Flói Nature Reserve).
It is a member of the Asteraceae family (= Compositae ), the daisy family. The Icelandic name of this species is Silfurhnappur.