Using a supermatrix approach to explore phylogenetic relationships, divergence times, and historical biogeography of saxifragales

The Saxifragales is a morphologically and ecologically diverse clade of flowering plants with a cosmopolitan distribution. Although families and genera within the order exhibit classic biogeographical disjunctions, no studies to date have rigorously examined and described its historical biogeography. Here, we analyze the historical biogeography of Saxifragales by first generating a new chronogram for the order using a supermatrix approach, based on 61 loci from 251 representative members of Saxifragales. Our results suggest that Saxifragales originated in the early Albian approximately 107 Ma and diversified rapidly in the next 15 Ma, with all stem lineages of extant families present by the Campanian at approximately 75 Ma. The ancestral geographic range of the order is unclear, but ancestral range reconstructions point to an East Asian origin as the most tenable hypothesis. Ancestral ranges of the Haloragaceae/Crassulaceae clade suggest a strong signal for an Australasia origin for all families, and Saxifragaceae shows strong signal for bidirectional movement across the Asian-Alaskan land bridge during the Upper Cretaceous. Disjunct distributions are best explained by long-distance dispersal rather than vicariance, but we demonstrate that timing and directionality within particular disjunctions are similar within Saxifragales and consistent with results from distantly related angiosperm clades.