Eight New Sedum Plastomes: Comprehensive Analyses and Phylogenetic Implications

<b>Background:</b><i>Sedum</i>, with the largest number of species in the family <i>Crassulaceae</i>, is a taxonomically complex genus and an important group of horticultural plants within this family. Despite extensive historical research using diverse datasets, the branching patterns within this genus and the family remain debatable. <b>Methods:</b> In this study, we conducted sequencing and comparative analyses of plastomes from eight <i>Sedum</i> species, focusing on the diversities in nucleotide, microsatellite repeats, putative RNA editing, and gene content at IR junctions. The phylogenetic inferences were further conducted at the order level-<i>Saxifragales</i>. <b>Results:</b> Our IR junction analyses of the eight investigated <i>Sedum</i> species detected a unique 110 bp IR extension into <i>rps19</i>, a feature highly conserved across <i>Crassulaceae</i> species, indicating a remarkably family-specific pattern. Additionally, we obtained 79 PCGs from 148 <i>Saxifragales</i> species and constructed a phylogenetic tree using a larger set of plastomes than in previous studies. Our results confirm the polyphyly of <i>Sedum</i> and reveal that <i>S. emarginatum</i> is more closely related to <i>S. makinoi</i> than to <i>S. alfredii</i>, which is sister to <i>S. plumbizincicola</i>. Furthermore, we also performed analyses of codon usage, putative RNA editing sites, and microsatellite repeats. <b>Conclusions:</b> These findings and the generated sequence data will enrich plastid resources and improve understanding of the evolution of <i>Sedum</i>, <i>Crassulaceae</i>, and <i>Saxifragales</i>.