Taxonomic revision of Korean Salix section Subviminales based on comparative morphology and complete plastome analysis

Salix section Subviminales, including only three species, is endemic to East Asia. In this study, we revised three species, S. gracilistyla, S. graciliglans, and S. blinii in Korea based on their plastomes and extensive morphological analyses to provide a comprehensive understanding of their taxonomic relationships. Based on our findings, we identified the morphological characteristics of S. blinii endemic to Korea, including its small size and distinct leaf shapes, which are well distinguished from both S. gracilistyla and S. graciliglans. Most of the morphological characteristics of S. gracilistyla and S. graciliglans overlapped, particularly leaf shape, floral structure, and growth habits. Next, we sequenced the plastomes of these three species using on high-throughput sequencing. The complete chloroplast genomes of the three Salix species ranged from 155,513 to 156,612 bp in length, including 112 unique genes; rps16, rpl32, and ycf68 were lost, which is typical within the genus. They have a conserved genome structure within the Salix genus, reflecting their close evolutionary relationships. Based on the plastome phylogenetic tree, S. blinii is sister to a large clade that includes three S. gracilistyla and other species. The three samples of S. gracilistyla were not monophyletic, possibly because of incomplete lineage sorting or hybridization events. Conclusively, S. blinii is taxonomically distinct owing to its smaller quantitative characteristics, whereas S. graciliglans is treated as a synonym for S. gracilistyla. This study provides valuable information for future research on Salix and contributes to the overall understanding of the genus.