Jimin Lee1, Jeongheon Park1, Sinyeong Park1, Jong-Soo Kang1P

1Department of Forest Resources, College of Forest and Environmental Sciences, Kangwon National University, Chuncheon 24341, Republic of Korea

The genus Spiraea L. (Rosaceae) comprises approximately 80–120 species distributed across temperate and subtropical regions of the Northern Hemisphere. Based on morphological characters, the genus has traditionally been divided into four sections. However, recent phylogenetic studies have shown that these sections are not monophyletic, particularly sect. Chamaedryon, and phylogenetic incongruence has been reported among different gene trees. To investigate the evolutionary history underlying these issues, we conducted a comprehensive phylogenetic reconstruction using transcriptome and plastid genome (plastome) data from 16 Spiraea taxa distributed in the Korean Peninsula, with Aruncus dioicus included as an outgroup, representing a total of 17 taxa. A total of 705 single- or low-copy nuclear genes were identified through orthologous gene selection and paralog removal. Phylogenetic analyses based on these nuclear genes revealed that Spiraea trichocarpa occupied two alternative phylogenetic positions, forming a sister relationship with five species of sect. Chamaedryon in 388 single-gene trees, while appearing as sister to sect. Glomerati in 317 single-gene trees. Species network inference using all 705 single-gene trees consistently supported a hybrid origin of S. trichocarpa across five proposed hypotheses, suggesting that it likely arose through hybridization between the common ancestor of the five species in sect. Chamaedryonand the common ancestor of sect. Glomerati. Phylogenetic analysis based on maternally inherited plastome data placed S. trichocarpa as sister to sect. Glomerati, indicating that the common ancestor of sect. Glomerati served as the maternal lineage. A haplotype-resolved genome study is currently underway to address this hypothesis in greater detail.