Phylotranscriptomics of Swertiinae (Gentianaceae) reveals that key floral traits are not phylogenetically correlated

Establishing how lineages with similar traits are phylogenetically related remains critical for understanding the origin of biodiversity on Earth. Floral traits in plants are widely used to explore phylogenetic relationships and to delineate taxonomic groups. The subtribe Swertiinae (Gentianaceae) comprises more than 350 species with high floral diversity ranging from rotate to tubular corollas and possessing diverse nectaries. Here we performed phylogenetic analysis of 60 species from all 15 genera of the subtribe Swertiinae sensu Ho and Liu, representing the range of floral diversity, using data from the nuclear and plastid genomes. Extensive topological conflicts were present between the nuclear and plastome trees. Three of the 15 genera represented by multiple species are polyphyletic in both trees. Key floral traits including corolla type, absence or presence of lobe scales, nectary type, nectary position, and stigma type are randomly distributed in the nuclear and plastome trees without phylogenetic correlation. We also revealed the likely ancient hybrid origin of one large clade comprising 10 genera with diverse floral traits. These results highlight the complex evolutionary history of this subtribe. The phylogenies constructed here provide a basic framework for further exploring the ecological and genetic mechanisms underlying both species diversification and floral diversity.

Automated summary

Establishing phylogenetic relationships among lineages with similar traits is crucial for understanding the origin of biodiversity on Earth. This study focused on the subtribe Swertiinae in the Gentianaceae family, which includes more than 350 species with diverse floral traits. Through phylogenetic analysis using nuclear and plastid genome data, the study revealed extensive conflicts between the trees constructed from the two genomes and the polyphyletic nature of three of the genera. Key floral traits showed random distribution without phylogenetic correlation. Additionally, the study suggested an ancient hybrid origin for a clade comprising 10 genera with diverse floral traits. These findings highlight the complex evolutionary history of the subtribe and provide a foundation for further research on species diversification and floral diversity.