PARNASSIACEAE (grass-of-Parnassus family)

One genus (but see below), about 50 species, North America, Europe, Asia.

The genus Parnassia has been included in the Saxifragaceae by most authors (Steyermark, 1963; Cronquist, 1991). However, recent phylogenetic studies (Morgan and Soltis, 1993; Soltis and Soltis, 1997; Zhang and Simmons, 2006) have shown that it is more closely related to the Celastraceae. The present treatment deviates from the standard practice in this manual of following the familial classification of Cronquist (1981, 1991) in treating Parnassia in its own family to reflect this new understanding of intergeneric relationships in the Saxifragales, as well as to make the Saxifragaceae more easily circumscribed and keyed.

Lepuropetalon spathulatum Muhl. ex Elliott, is a tiny annual with a highly disjunct distribution in wet, sandy, disturbed areas in the southeastern United States, Mexico, and portions of South America. It is often placed in the Parnassiaceae, but sometimes segregated into its own family, the Lepuropetalaceae. The biology and systematics of this odd plant, which is easily overlooked in the field, require further study.