SYSTEMATICS, TAXONOMY AND BIOGEOGRAPHY OF THE COSMOPOLITAN AND FOSSIL-RICH BUCKTHORN FAMILY (RHAMNACEAE JUSS.)

My thesis combines taxonomy, phylogenetics, divergence time estimations and ancestral area reconstructions, nomenclature, and other methods to shed light on the evolutionary processes that shaped the extant biodiversity of the buckthorn family (Rhamnaceae Juss.). In a first step, this thesis provides a major contribution to the taxonomic assessment and arrangement within the buckthorns. By describing the new genus Pseudoziziphus Hauenschild, and resurrecting four genera, this thesis highlights and compensates underestimated diversity. Simultaneously, it provides a phylogenetic framework based on the largest molecular data set in the family so far. In a second step, the taxonomic and phylogenetic framework was used to reconstruct solid divergence time estimates and ancestral area estimates for Rhamnaceae, with a focus on the ziziphoid lineage, and the genus complex Alphitonia Reissek ex Endl. sensu lato. By this, it was possible to unravel evolutionary processes within the history of Rhamnaceae and provide a biogeographic scenario for the ziziphoid lineages, including Alphitonia s.l.:General Introduction 1 Bibliography 19 Chapter 1 36 Phylogenetic relationships within the cosmopolitan buckthorn family (Rhamnaceae) support the resurrection of Sarcomphalus and the description of Pseudoziziphus gen. nov. 37 Bibliography 48 Appendix 1 50 Supplements 55 Chapter 2 56 Analysis of the cosmopolitan buckthorn genera Frangula and Rhamnus s.l. supports the description of a new genus, Ventia 57 Bibliography 67 Appendix 1 68 Supplements 71 Erratum 72 Chapter 3 74 The influence of the Gondwanan break-up on the biogeographic history of the ziziphoids (Rhamnaceae) 75 Bibliography 96 Appendix 1 105 Appendix 2 115 Supplements 117 Chapter 4 118 Biogeographic analyses support an Australian origin for the IndomalesianAustralasian wet forest-adapted tropical tree and shrub genus Alphitonia and its close allies (Rhamnaceae) 119 Bibliography 144 Appendix 1 153 Appendix 2 161 Appendix 3 166 General Conclusions 172 Bibliography 182 Appendix 186 Spatio-temporal evolution of Allium L. in the Qinghai-Tibet-Plateau region: Immigration and in situ radiation 187 Curriculum Vitae 200 Declaration of Independent work 207 Author contributions 20