genus of deciduous shrubs of the family Hydrangeaceae, including the popular garden forms commonly known as mock orange (from its characteristic orange-blossom fragrance) and sweet syringa. Philadelphus, comprising about 65 species, is native to northern Asia and Japan, the western United States, the southern Atlantic coast of the United States, and Mexico. These decorative and fragrant shrubs bloom in the late spring and grow unusually well in dry soils.