Phylogenetic relationships in Saxifragaceae sensu lato: A comparison of topologies based on 18S rDNA and rbcL sequences

Relationships among the morphologically diverse members of Saxifragaceae sensu late were inferred using 130 18S rDNA sequences. Phylogenetic analyses were conducted using representatives of all 17 subfamilies of Saxifragaceae sensu late, as well as numerous additional taxa traditionally assigned to subclasses Magnoliidae, Caryophyllidae, Hamamelidae, Dilleniidae, Rosidae, and Asteridae. This analysis indicates that Saxifragaceae should be narrowly defined (Saxifragaceae sensu stricto) to consist of similar to 30 herbaceous genera. Furthermore, Saxifragaceae s. s. are part of a well-supported clade (referred to herein as Saxifragales) that also comprises Iteoideae, Pterostemonoideae, Ribesioideae, Penthoroidene, and Tetracarpaeoideae, all traditional subfamilies of Saxifragaceae sensu late, as well as Crassulaceae and Haloragaceae (both of subclass Rosidae), Paeoniaceae (Dilleniideae), and Hamamelidaceae, Cercidiphyllaceae, and Daphniphyllaceae (all of Hamamelidae). The remaining subfamilies of Saxifragaceae sensu lato fall outside this clade. Francoa (Francooideae) and Bauera (Baueroideae) are allied, respectively, with the rosid families Greyiaceae and Cunoniaceae. Brexia (Brexioideae), Parnassia (Parnassioideae), and Lepuropetalon (Lepuropetaloideae) appear in a clade with Celastraceae. Representatives of Phyllonomoideae, Eremosynoideae, Hydrangeoideae, Escallonioideae, Montinioideae, and Vahlioideae are related to taxa belonging to an expanded asterid clade (Asteridae sensu late). The relationships suggested by analysis of 18S rDNA sequences are highly concordant with those suggested by analysis of rbcL sequences. Furthermore, these relationships are also supported in large part by other lines of evidence, including embryology, serology, and iridoid chemistry.