Historical hybridization and asymmetric introgression in two sympatric species of Paepalanthus (Eriocaulaceae)

While interspecific hybridization is a recognized key driver of plant diversification in recently diverged lineages, the resulting introgression can generate complex patterns of genetic and morphological variation that often challenge the recognition of species boundaries. In Paepalanthus (Eriocaulaceae), interspecific hybridization has long been hypothesized but remains largely underexplored, particularly from a genetic perspective. Here, we investigate the evolutionary dynamics of hybridization between two sympatric species of Paepalanthus in Central Brazil by integrating morphological and population genomic analyses. Our morphological assessments revealed that hybrids generally exhibited intermediate or asymmetric trait expression and a lack of gynoecium development, suggesting reduced female fertility. Genomic analyses identified an absence of contemporary F 1 hybrids, with most individuals assigned to advanced-generation hybrid classes. Furthermore, we detected bidirectional and asymmetric introgression, characterized by contrasting patterns of allele sharing, while morphological traits were decoupled from genomic ancestry, highlighting the mosaic nature of hybrid genomes. These results provide the first integrative evidence of natural hybridization in Paepalanthus , suggesting incomplete reproductive isolation and recurrent introgression between divergent lineages, thereby emphasizing the role of reticulate evolution in shaping diversification and species boundaries within this group.