MATK AND RBCL GENE SEQUENCE DATA INDICATE THAT SAXIFRAGA (SAXIFRAGACEAE) IS POLYPHYLETIC

The large genus Saxifraga, which consists of 2400 morphologically and cytologically diverse species, has long been considered taxonomically complex. Phylogenetic analysis of over 2500 bp of chloroplast sequence data derived from matK and rbcL was employed to examine relationships among sections of Saxifraga, the segregate genera Zahlbrucknera, Saxi fragopsis, and Cascadia, and the relationships of these taxa to other Saxifragaceae sensu stricto. Phylogenetic trees resulting from separat e analyses of the matK and rbcL sequences were highly congruent; phylo genetic analysis of a combined matK-rbcL data matrix was therefore als o conducted. Our analyses indicate that Saxifraga is polyphyletic, com prising two well-differentiated clades. One clade, Saxifraga sensu str icto, is the sister to the remainder of the family and consists of Sax ifraga sections Irregulares, Heterisia, Trachyphyllum, Cymbalaria, Mes ogyne, Xanrhizoon, Porphyrion, Ciliarae, Cotylea, Ligulatae, Saxifraga , and Gymnogera. With the exception of Gymnopera, the species-rich sec tions of this clade are monophyletic, Also part of this clade is the p roblematic Zahlbrucknera paradoxa, which is allied with members of sec tion Saxifraga. A second major clade of Saxifraga species, Micuanthes sensu late, comprises the large section Micranthes, as well as the seg regate genus Cascadia, and S. tolmiei of section Merkianae. This clade is allied with the Heuchera, Darmera, and Chlysosplenhm-Peltoboykinia groups of genera. The segregate genus Saxifragopsis is only distantly related to species of Saxifraga, and is instead the sister to Astilbe . The monotypic Oresitrophe is confirmed as a member of the Darmera gr oup of genera. These results suggest that the floral features used to define Saxifraga may simply be symplesiomorphic in these well-separate d Saxifraga lineages. Furthermore, the enormous cytological diversity encompassed by Saxifraga likely represents two independent instances o f extensive aneuploidy and polyploidy in Saxifragaceae.