a cultivated shrub (Spiraea prunifolia) of the rose family, bearing numerous small, white double flowers in the spring
See bridal wreath in American Heritage Dictionary 4
or bri·dal-wreath(brīdˈl-rēth)
noun
Any of various shrubs of the genus Spiraea, such as S. prunifolia, having arching branches covered with white bloom. Bridal wreath is popular as an ornamental and in flower arrangements.