Phylogenetic analyses of Searsia (Anacardiaceae) from eastern Asia and its biogeographic disjunction with its African relatives

• First presentation of the phylogenetic and biogeographic relationships of Searsia.
• Eastern Asian Searsia was monophyletic closely related to the African Searsia.
• A reticulate evolution resulted from a hybrid/introgressed lineage was deduced.
• The closure of Tethys would enable an expansion of the African Searsia to Asia.

Searsia is an Old World genus in the sumac family Anacardiaceae segregated from the Rhus complex. The genus is widely distributed in Africa with three species in eastern Asia, of which Searsia paniculata was commonly recognized as Terminthia paniculata in China. In this study, we conducted phylogenetic analyses of the eastern Asian Searsia to test the relationships to the African relatives, based on both nuclear (ETS and ITS) and chloroplast (trnL–F and ndhF) sequences. Phylogenetic analyses based on different genomic sequences strongly support that the Searsia taxa from eastern Asia are monophyletic. However, topological incongruence is observed between the nuclear and chloroplast data, especially concerning the phylogenetic position of the eastern Asian group. The divergence time of the genus between eastern Asia and Africa was dated to 23.36 Ma (million years ago), with a 95% highest posterior density (HPD) of 14.30–36.31 Ma, using the Bayesian relaxed-clock estimation. It is hypothesized that the closure of the Tethys Sea and the formation of the “Gomphotherium Landbridge” likely had enabled the expansion of the Searsia lineage between Africa and Asia in the late Oligocene to early Miocene.