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Dryad

Supplemental data for: Lineage diversification and rampant hybridization among subspecies explain taxonomic confusion in the endemic Hawaiian fern Polypodium pellucidum

Abstract

Premise: Polypodium pellucidum, a fern endemic to the Hawaiian Islands, encompasses a broad spectrum of morphological and ecological variation, suggesting a complex history involving divergence and hybridization. In contrast to angiosperm systems, spore dispersal in ferns presents a unique opportunity to study how highly dispersible organisms diversify in the dynamic landscape of the archipelago.

Key Results: We infer P. pellucidum is monophyletic, dispersing to the Hawaiian archipelago 11.53 to 7.77 Mya, with diversification into extant clades 5.66 to 4.73 Mya. We identify four non-hybrid clades with unique morphologies, ecological niches, and distributions. Additionally, we elucidate several intraspecific hybrid combinations and evidence for undiscovered or extinct 'ghost' lineages contributing to extant hybrids populations.

Conclusions: We provide a roadmap for revising the taxonomy of P. pellucidum to account for cryptic lineages and intraspecific hybrids. Geologic succession of the Hawaiian Islands through cycles of volcanism, vegetative succession, and erosion has determined the available habitats and distribution of ecologically specific divergent clades within P. pellucidum, with intraspecific hybrids arising as a result of ecological and or geological transitions, often persisting after the local extinction of their progenitors. This research contributes to our understanding of the evolution of Hawaii's diverse fern flora and allows for better conservation efforts that are often complicated by the presence of cryptic taxa and hybridization.