Elucidating time divergence and biogeography of Euonymus sect. Biloculares using comprehensive plastid genome analysis

Scientists have devoted considerable time to understanding the inter and intracontinental dispersal worldwide. However, Euonymus L, is the largest species containing, and worldwide distributed genus in Celastraceae, less focus has been given to its distribution and origin. Euonymus L. was taxonomically separated into two sections based on the number of cells: E. sect. Uniloculares possesses one-celled anthers and are primarily found in Asia, and globally distributed E. sect. Biloculares containing two-celled anthers. This study focused on the investigation of the chloroplast genome of E. sect. Biloculares. The plastome size of E. sect. Biloculares range from 156,881 to 158434 and, exhibit a common quadripartite structure. With few exceptions, the structure of the genomes is conserved. In contrast to E. sect. Uniloculares, E. americanus, E. spraguei, E. pauciflorus, E. verrucosus and E. hamiltonianus M, have ndhF as a pseudogene which is different from other members of E. sect. Biloculares used in these studies. In all the investigated species rps16 lacked introns. Additionally, IR junction analysis revealed a non-constant variation in expansion and shrinkage. rps19 is located in the LSC of E. pauciflorus, whereas rps19 and rpl22 were located in the IR region of E. verrucosus. The phylogeny of Euonymus L. (25 species) was inferred using the complete plastid genome. Phylogenetic analysis based on 80 protein-coding genes showed that E. sect. Biloculares is a non-monophyletic group that originated in East Asia during the in Cenozoic era. Disjunction and vicariance in East and West Asia and North America were also found in E. sect. Biloculares. This study provides information about the variability in the complete plastid genomes, phylogeny, age estimation, and biogeography of E. sect. Biloculares.