The Collaborative International Dictionary
Spiraea prunifolia
bridalwreath \bridalwreath\ n. a shrub ( Spiraea prunifolia) having copious small white flowers in spring.
Syn: bridal wreath, Saint Peter's wreath, St. Peter's wreath.
Wikipedia
Spiraea prunifolia
Spiraea prunifolia, commonly called bridalwreath spirea, is a species of the genus Spiraea, sometimes also spelled Spirea. It flowers mid-spring, around May 5th, and is native to Japan, Korea, and China.