Pronunciation: (lOOs'strīf"),[key] —n. 1. any of various plants belonging to the genus Lysimachia, of the primrose family, having clusters of usually yellow flowers, as L. vulgaris(garden loosestrife) or L. quadrifolia(whorled loosestrife). 2. any of several plants belonging to the genus Lythrum, of the loosestrife family. Cf. purple loosestrife.