Premise: Hybridization is recognized as an important mechanism in fern speciation, with many well-studied examples of allopolyploids forming among congeners, as well as evidence of ancient genome duplications. Several contemporary instances of deep (intergeneric) hybridization have been noted, invariably resulting in sterile progeny. We chose the christelloid lineage of the family Thelypteridaceae to investigate recent hybridization between deeply diverged lineages among extant taxa. We also seek to understand the ecological and evolutionary outcomes of resulting lineages across the landscape.

Methods: By phasing captured reads within a phylogenomic dataset of GoFlag 408 nuclear loci using HybPhaser, we investigated candidate hybrids to identify parental lineages within the christelloid clade. We estimated divergence ages by inferring a dated phylogeny using fossil calibrations with treePL. We investigated ecological niche conservatism between one confirmed intergeneric allotetraploid and its diploid progenitors using the centroid, overlap, unfilling, and expansion (COUE) framework, based on PCA.

Key Results: We provide evidence for at least six instances of intergeneric hybrid speciation within the christelloid clade, and estimate up to 45 million years of divergence between progenitors. The niche quantification analysis showed moderate niche overlap between an allopolyploid species and its progenitors, with significant divergence from the niche of one progenitor and conservatism to the other.

Conclusions: The examples provided here highlight the overlooked role that allopolyploidization following intergeneric hybridization may play in fern diversification and range and niche expansions. Applying this approach to other fern taxa may reveal a similar pattern of deep hybridization resulting in highly successful novel lineages.

Please refer to the methods section of the associated publication for a detailed description of datasets and analyses.