Elucidating time divergence and biogeography of Euonymus hamiltonianus complex using complete plastome analysis

The evolutionary history of Euonymus L., within the Celastraceae family has been understudied. Within this genus E. hamiltonianus Wall., belonging to E. sect. Biloculares have slight variations in morphology due to their high ecological range, leading to different varieties and subspecies. This has caused debate on the species status of many taxa. This study we investigate the plastome of E. hamiltonianus complex and related species in E. sect. Biloculares. It was aimed to observe the similarities and differences in the plastome, to clarify the ambiguities and evolutionary relationships within this complex. Plastome showed high similarities in coding regions and conserved quadripartite structure (156,881-158,434 bp). E. hamiltonianus complex had rps19 located in the LSC region. ndhF was reportedly a pseudogene in E. hamiltonianus (Mugabsan, South Korea). In all the investigated species, rps16 lacked introns. A resolved relation was observed among the taxa of E. hamiltonianus complex, and the species closely related to these (100% Bootstrap & 1.0 PP). E. sieboldianus Blume was observed at a position between the two taxa of E. hamiltonianus, making it a possible synonymy. E. europaeus L., and E. velutinus Fisch. & C.A.Mey., formed separate lineages. Molecular dating suggests that E. hamiltonianus complex originated in East Asia during the Middle Miocene Transition, which is a significant phase within the Neogene era, supporting the hypothesis that Euonymus originated in East Asia and E. hamiltonianus complex is estimated to develop in East Asia and diversified across the Far East during this period.