Phylogeny, Divergence Times, And Biogeography Of Saxifragaceae

Saxifragaceae (Saxifragales) in APG III, contain approximately 640 species and 33 genera, about half of which are monotypic. Due to factors such as morphological stasis, convergent morphological evolution, and disjunct distributions, relationships within Saxifragaceae have historically been problematic. The family primarily occurs in mountainous regions of the Northern Hemisphere, with the highest generic and species diversity in western North America, but disjunct taxa are known from southern South America. The chromosome number of Saxifragaceae are from 2n= 14 to 220. Taxa within Saxifragaceae have been used as model groups for studying polyploid speciation, biogeography/phylogeography and evolution and diversification.Here, we integrate broad gene (56 loci) and taxon (223 species) sampling strategies, both the most comprehensive to date within Saxifragaceae, with fossil calibrations and geographical distribution data to address relationships, divergence times, and historical biogeography among major lineages of Saxifragaceae. The following is the results of this research:(1) Two previously recognized main clades, the heucheroids (eight groups +Saniculiphyllum) and saxifragoids (Saxifraga s.s.), were re-affirmed by our phylogenetic analyses. Relationships among the eight heucheroid groups, as well as the phylogenetic position of Saniculiphyllum within the heucheroids, were resolved with mostly high support. Heucheroids was composed of Eight groups and Saniculiphyllum guangxiense. Within Saxifraga s.s., Saxifraga and Saxifragella bicuspidata (Hook, f.) were included; but not involving Micranthes which was supposed to belong in Saxifraga. Genus Micranthes was clustered with Peltoboykinia group as sister relationships. The Saniculiphyllum guangxiens, as the endemic species in southern China, was not resolve its position within Saxifragaceae because of lacking this sample or no enough DNA data including. In this study, Saniculiphyllum guangxiense should be included into Heucheroideae (Heucheroids) with strong BI PP and ML BS support values.(2) Our analyses indicate that Saxifragella bicuspidata, a species endemic to Tierra del Fuego in southern South America and the only species in the genus, is an early-diverging member of the primarily north temperate genus Saxifraga. Based on previous rstudies, specimen in Herbarium, and our analysis, Saxifragella bicuspidata should be included within the large genus Saxifraga, and we therefore accept the name Saxifraga bicuspidata for this species, and the formal nomenclature (Saxifraga bicuspidata Hook. f.).(3) Divergence time estimates indicate that Saxifragaceae began to diversify ca.38.37 million years ago (MYA; 95%HPD= 30.99-46.11 MY A) in the Mid-Late Eocene, and that the two major lineages, the heucheroids and saxifragoids, began to diversify approximately 30.04 MYA (95%HPD= 23.87-37.15 MYA) and 30.85 MYA (95% HPD= 23.47-39.33 MYA), respectively.(4) We reconstructed ancestral geographic areas using statistical dispersal-vicariance (S-DIVA). These analyses indicate several radiations within Saxifragaceae:one in eastern Asia and multiple radiations in western North America. Long-distance dispersal and vicariance events have both played important roles in generating the diversity within this family, and there was likely considerable interchange of Saxifragaceae between eastern Asia and western North America via the Bering Land Bridge until the Late Miocene.(5) Our results also demonstrate that large amounts of sequence data coupled with broad taxon sampling can help resolve clade relationships that have thus far seemed intractable within Saxifagaceae, and also for phylogenetic studies of other taxa.