Nuclear loci developed from multiple transcriptomes yield high resolution in phylogeny of scaly tree ferns (Cyatheaceae) from China and Vietnam

The scaly tree ferns, Cyatheaceae, form a large natural group of ca. 640 species. They comprise an ideal model for studying the biogeography of plants due to their broad distribution across the tropical to south-temperate areas of the world. However, tracing the biogeographic history of this highly diversified group has been hampered by unresolved evolutionary relationships among the major clades. Here, we generated transcriptome sequences of five species in three genera of Cyatheaceae (Alsophila, Gymnosphaera, and Sphaeropteris) and used them to search for single-copy nuclear loci for phylogenetic reconstruction. We identified a total of 818 candidate single-copy loci across multiple Cyatheaceae species. To test their phylogenetic utility, we further obtained sequence data of 12 of these loci for 76 samples representing all 13 known species of scaly tree ferns in China and Vietnam. Phylogenetic analyses based on multispecies coalescent and, alternatively, concatenation models yielded congruent results with high resolution. Additionally, we used the 12 loci to identify genetic signals of hybridization. Overall, our results demonstrated that multiple, single-copy loci are informative and efficient tools for phylogenetic or evolutionary studies of scaly tree ferns.