Phylogenomic study of Orostachys using Angiosperms353: Polyphyly of subsections with taxonomic consequences

Ha-Rim Lee¹Halam Kang¹Yoo-Jung Park¹Ho-Kwon Kwak¹Hyeyeon Kim¹Jieun Park¹Hyeok Jae Choi²Kyung-Ah Kim^3*Kyeong-Sik Cheon^1*

• ¹Sangji University, Wonju, Republic of Korea
• ²Changwon National University, Changwon, Republic of Korea
• ³Kangwon National University, Chuncheon-si, Republic of Korea

The genus Orostachys (Crassulaceae) has been subject to considerable disagreement regarding its taxonomic boundaries because of extensive morphological similarities among taxa and widespread intraspecific variation. Additionally, previous phylogenetic studies based on molecular markers have consistently demonstrated that the two subsections of Orostachys (subsect. Orostachys and subsect. Appendiculatae) do not constitute a monophyletic group, leaving the generic boundaries unresolved to date. Therefore, we aimed to evaluate the generic boundaries and accurate taxonomic positions of individual taxa via the Angiosperms353 target enrichment approach. We analyzed a total of 43 individuals representing 25 taxa from 5 genera, including 14 Orostachys taxa and closely related genera such as Hylotelephium and Meterostachys. High-quality genomic data were obtained, with an average gene recovery rate of 99.1% (349.5/353 genes) and substantial sequence length recovery (average 1,223 bp per locus), resulting in concatenated datasets of 397-400 kbp sequences. Phylogenetic analyses using concatenation and coalescent-based approaches with datasets based on different threshold values revealed exceptionally high concordance across all the phylogenetic trees, demonstrating the high reliability of our results. Our findings confirmed the polyphyletic nature of Orostachys, with O. subsect. Orostachys forming a monophylum distinct from O. subsect. Appendiculatae and related genera. Particularly significant is our discovery that, unlike previous studies, O. subsect. Orostachys constituted a monophyletic group rather than exhibiting a paraphyletic relationship with Hylotelephium, which we consider the most important finding of this study. At the species level, we resolved several taxonomic issues. O. ramosa and O. japonica f. polycephala were confirmed as synonyms of O. malacophylla and O. japonica, respectively. Furthermore, the endemic Korean species O. margaritifolia, O. latielliptica, O. chongsunensis, and O. iwarenge f. magnus were effectively identified as independent taxa. Most nodes in the phylogenetic tree constructed in this study had UFBoot values ≥95% and LPP values ≥0.95, indicating high reliability. Therefore, this study represents another demonstration of the effectiveness of the Angiosperms353 approach in resolving complex evolutionary relationships within morphologically challenging plant groups.