Caltha palustris; The marsh-marigold is typically a plant of the lowlands but is very sensitive to salinity. It is quite a conspicuous plant growing along streams, bogs and roadsides. From Icelandic farmers I heard this plant gives much joy to the people as it announces with their blooms in spring the end of winter and heralds the coming summer.
It is a member of the Ranunculaceae (buttercup family). The Icelandic name of this species is Hófsóley or Lækjasóley.