Eight New Sedum Plastomes: Comprehensive Analyses and Phylogenetic Implications

Background: Sedum, with the largest number of species in the family Crassulaceae, 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. Methods: In this study, we conducted sequencing and comparative analyses of plastomes from eight Sedum 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—Saxifragales. Results: Our IR junction analyses of the eight investigated Sedum species detected a unique 110 bp IR extension into rps19, a feature highly conserved across Crassulaceae species, indicating a remarkably family-specific pattern. Additionally, we obtained 79 PCGs from 148 Saxifragales species and constructed a phylogenetic tree using a larger set of plastomes than in previous studies. Our results confirm the polyphyly of Sedum and reveal that S. emarginatum is more closely related to S. makinoi than to S. alfredii, which is sister to S. plumbizincicola. Furthermore, we also performed analyses of codon usage, putative RNA editing sites, and microsatellite repeats. Conclusions: These findings and the generated sequence data will enrich plastid resources and improve understanding of the evolution of Sedum, Crassulaceae, and Saxifragales.