Monophyly and relationships of the enigmatic family Peridiscaceae

A brief history of Saxifragales. — The composition of Saxifragales as revealed in recent analyses is one of the major surprises of molecular phylogenetic studies of angiosperms (e.g., Chase & al., 1993; Morgan & Soltis, 1993; D. Soltis & al., 1997a, 2000; Qiu & al., 1998; Hoot & al., 1999; P. Soltis & al., 1999; Savolainen & al., 2000a, b; reviewed in D. Soltis & al., 2005). The order (APG II, 2003) now includes Altingiaceae, Cercidiphyllaceae, Crassulaceae, Daphniphyllaceae, Grossulariaceae, Haloragaceae s.l. (expanded to include Tetracarpaeaceae, Penthoraceae, and Aphanopetalum [formerly of Cunoniaceae]), Hamamelidaceae, Iteaceae, Paeoniaceae, Pterostemonaceae (some times included in Iteaceae; APG II, 2003), and Saxifragaceae. The circumscription of Saxifragales based on molecular data departs markedly from previous morphology-based classifications, which placed these families in three different subclasses (e.g., Cronquist, 1981; Takhtajan 1997; Morgan & Soltis, 1993; Qiu & al., 1998; reviewed in Soltis & al., 2005): Altingiaceae, Hamamelidaceae, Cercidiphyllaceae, and Daphniphyllaceae were placed in Hamamelidae; Saxifragaceae, Iteaceae, Pterostemonaceae, Grossulariaceae, Crassulaceae, and Haloragaceae s.l. were treated in Rosidae; and Paeoniaceae were placed in Magnoliidae or Dilleniidae (reviewed in Cronquist, 1981). Several members of Saxifragales were considered closely related in some previous classifications: Saxifragaceae, Grossulariaceae, Iteaceae, Pterostemonaceae, Penthoraceae, and Tetracarpaeaceae were considered Monophyly and relationships of the enigmatic family Peridiscaceae