Stonecrop

White stonecrop is a mat-forming, evergreen succulent of the stonecrop family, native to Europe, north Africa and western Asia and widely grown as a rock plant. Wikipedia says its fleshy, nearly cylindrical leaves are sometimes tinged with pink in drought, and that in July and August the stems lengthen and carry dense cymes of starry white flowers with five petals and ten stamens. Grieve says it is found on rocks and walls and, when it grows on garden walls and cottage roofs, is a garden escape. She notes that Culpeper called it the small houseleek, that older herbalists used it for inflammation, and that it was pickled and eaten.