Exploring the evolutionary history of Sinocrassula (Crassulaceae) to provide a case study for the tree of life in succulent plants

Abstract

Sinocrassula (Crassulaceae), a small genus of Crassulaceae, distributed mainly in the Himalayan-Hengduan Mountains (HHM). In this study, with an extensive taxon samples of Sinocrassula to date, we utilized both plastomes and single-copy nuclear genes from genome skimming and transcriptome approaches to reconstruct a well-supported phylogeny and infer historical biogeographical processes, along with current distributional data. Our major results include: (1) the monophyly of Sinocrassula; (2) significant cytonuclear discordance and gene tree conflict were detected within Sinocrassula, and can be explained by incomplete lineage sorting and hybridization; (3) the genus Sinocrassula exhibits significant genome size variations, but chromosome counts suggested that they are all diploid, which may be related to hybridization and post-polyploid genome diploidization (PPD); (4) the dating result showed that Sinocrassula did not originate before the Miocene; (5) the early rapid diversification and rapid radiation of Sinocrassula in the HHM is most likely associated with the warm climate of the mid Miocene, the mountain building of the HHM, the East Asian monsoons, and environmental heterogeneity caused by the rapid incision of rivers. Our study presented here will help understand the evolution of flora of HHM and provide robust references for the speciation and evolutionary history of Crassulaceae.