Phylogenomic reconstruction reveals deep reticulate evolutionary history and polyphyletic genus (Boeica) in the subtribe Leptoboeinae (Gesneriaceae), with description of a novel genus

The subtribe Leptoboeinae (Gesneriaceae) has undergone numerous taxonomic revisions due to ambiguous generic boundaries, complicating conservation and utilization efforts. In this study, we employed transcriptomes from a representative clade within the subtribe to construct a low-copy nuclear (LCN) gene data set. Plastid genomes and LCN genes, assembled from 66 samples, were used to investigate the phylogenetic structure, reticulate evolution and divergence times among the species of this subtribe. Firstly, phylogenetic analysis revealed that Boeica is polyphyletic and identified a new genus, Crassicaulis, which forms a sister group to the remaining genera within the subtribe. Secondly, complex cytonuclear conflicts and gene tree incongruence at genus-level nodes were identified. Multiple lines of evidence revealed two reticulate evolutionary events within this lineage, suggesting that Boeica porosa and B. stolonifera, as well as Boeica enpingensis, underwent hybridization during their speciation processes. Finally, divergence time estimation revealed that most genera emerged between 17 and 12 Ma. This study provides a well-resolved phylogenetic framework for the subtribe Leptoboeinae, describes a new genus and elucidates the subtribe’s intricate reticulate evolutionary history. Furthermore, we propose that the mid-Miocene East Asian monsoon played a pivotal role in the diversification of this lineage.