The mock oranges - Philadelphus spp. - have been placed in several families: Saxifragaceae (Harrington 1954), Hydrangeaceae (Hitchcock and others 1961), and more recently, the Philadelphaceae (Hickman 1993). Hydrangeaceae, however, is the most widely accepted placement (Cronquist and others 1997; USDA NRCS 2001). There are about 50 to 65 species of mock orange, occurring primarily in temperate and subtropical areas of the Northern Hemisphere. Four or five species are native to the United States. Two of these - Lewis mock orange (Philadelphus lewisii Pursh) and littleleaf mock orange (P. microphyllus Gray) - occur in the western United States and are used in wildland as well as in ornamental plantings (table 1). Both western species are erect to rounded, multi-stemmed, deciduous shrubs with opposite, entire or nearly entire leaves and fragrant white flowers (Hickman 1993; Munz amd Keck 1973; Welsh and others 1987).
Shaw, Nancy L.; Hurd, Emerenciana G.; Stickney, Peter F. 2008. Philadelphus L.: mock orange. In: Bonner, Franklin T.; Karrfalt, Robert P., eds. The Woody Plant Seed Manual. Agric. Handbook No. 727. Washington, DC. U.S. Department of Agriculture, Forest Service. p. 786-789.