A1 Refereed original research article in a scientific journal
Resolving fuzzy species limits: nuclear evidence for speciation by hybridisation in Amazonian Trichomanes ferns; 
Authors: Frederiksen, Laura Kragh; Sundström, Jami; Eiserhardt, Wolf L.; Tuomisto, Hanna
Publisher: Elsevier BV
Publication year: 2026
Journal: Molecular Phylogenetics and Evolution
Article number: 108674
Volume: 224
ISSN: 1055-7903
eISSN: 1879-2707
DOI: https://doi.org/10.1016/j.ympev.2026.108674
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Partially Open Access publication channel
Web address : https://doi.org/10.1016/j.ympev.2026.108674
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/526971427
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Unclear species boundaries are a common challenge in ecological studies and species inventories, obscuring patterns of biodiversity and complicating inferences about ecological and evolutionary processes. One possible cause of fuzziness is hybridisation, but little information exists on hybridisation in the tropics. Here we aim to address the question of potential hybridisation in the tropical American fern genus Trichomanes (Hymenophyllaceae) and to clarify evolutionary relationships within the genus. We take advantage of nuclear target-capture sequencing, haplotype phasing and off-target plastid reads to detect phylogenetic relationships and reticulate histories. We sampled 303 individuals that represent 41 known Trichomanes species. Our analyses recovered a robust backbone for the genus, strongly supporting subgenus Trichomanes as sister to subgen. Feea, and subgen. Davalliopsis as sister to subgen. Lacostea. Trichomanes pinnatum proved to be a complex where six different unnamed morphs represent four different kinds of evolutionary history. Two morphs appear to be stabilised, relatively old hybrid-derived species, one represents a recent hybrid, one reflects repeated spontaneous hybridisation between the same parent species, and one represents within-species morphological variation without any obvious genomic signal. Excluding the four hybrids makes T. pinnatum s.s. morphologically and genetically much more uniform, but its geographic distribution still covers practically all tropical America, indicating that the species may be approaching panmixia.
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Funding information in the publication:
Funding from Aarhus University Research Foundation (grant AUFFE-2023-7-3 to HT), Danish National Research Foundation (grant DNRF179 to HT), and Research Council of Finland (grant 351460 to HT) is gratefully acknowledged.