Cerastium tomentosum
Cerastium tomentosum (Snow-in-summer) is a flowering plant.
It grows in a low, spreading clump. The stems are silvery-grey, the flowers white and about 15 mm across.
Cerastium tomentosum is best grown in dry, sandy, well-drained soils in full sun. It can be used as a groundcover or in rock gardens.
Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Cerastium tomentosum". Image Credit.