Comparative Analysis of the Chloroplast Genomes of the Melliodendron (Styracaceae) Species: Providing Insights into Molecular Evolution and Phylogenetic Relationships

<i>Melliodendron xylocarpum</i> is a member of the Styracaceae family, which is well-known for its remarkable ornamental and medicinal properties. In this research, we conducted comparative analysis of the chloroplast genomes from four samples of <i>M. xylocarpum,</i> representing <i>Melliodendron</i>. The results demonstrated that the chloroplast genome of four <i>M. xylocarpum</i> samples ranging from 157,103 bp to 158,357 bp exhibited a typical quadripartite structure, including one large single-copy (LSC) region (90,131 bp to 90,342 bp), one small single-copy (SSC) region (18,467 bp to 18,785 bp), and two inverted repeat regions (IRs) (24,115 bp to 24,261 bp). Different levels of expansion and contraction were observed in the IR region of four <i>M. xylocarpum</i> samples. Besides, <i>accD</i> and <i>ycf1</i> have been identified under positive selection, potentially linked to the adaptive response of <i>Melliodendron</i> to various environmental changes. Conflicting phylogenetic relationships were identified among various genera within the Styracaceae family in the phylogenetic tree constructed using CDS sequences and complete chloroplast genomes. Furthermore, the significance of a large sample size was also highlighted in this study for enhancing the accuracy of findings from phylogenetic analyses. The findings of this research will provide significant insights for future investigations into the evolutionary trends and conservation of the <i>Melliodendron</i> species.