Orlaya grandiflora

Orlaya grandiflora, the white laceflower, is a species of flowering plant in the family Apiaceae, native to Mediterranean Europe. Growing to, this is a multi-branched annual with divided ferny leaves, and flattish panicles of pure white flowers over a long period in summer. The uneven size of the individual florets gives it the appearance of lace, especially when planted in large swathes.
It is a recipient of the Royal [Horticultural Society]'s Award of [Garden Merit]. It prefers a sunny, well-drained position.