Windflower. In swedish it's called vitsippa.

Windflower starts blooming soon after the foliage emerges from the ground.
The leaves are divided into three segments and the flowers, produced on short stems, are held above the foliage with one flower per stem. They grow from underground root-like stems called rhizomes and the foliage dies back down by mid summer.
The flower is open on daytime, in the evening it's closed and hanging to the ground.
The flower is 2 cm diameter, with six or seven petal-like segments with many stamens. In the wild the flowers are usually white, but may be pinkish, lilac, blue or yellow and often have a darker tint to the back of the 'petals'.
(This information comes from Wikipedia).

Yesterday I picked some windflowers and put them in a vase. I've been told when taking away two of three leaves you have much longer pleasure of these flowers.