What is Nephrolepis ‘bostoniensis’?: Unravelling the origin of Nephrolepis hybrids and cultivars with molecular data

• We used gapCp and chloroplast markers successfully to study hybridity in Nephrolepis.
• Nephrolepis “bostoniensis” originated by hybridization.
• Hybridization in Nephrolepis has repeatedly bridged a deep gap in the phylogeny.
• Hybridization in Nephrolepis has repeatedly produced plants similar to N. exaltata.

Hybridization, polyploidization, and reticulate evolution are major mechanisms that shape the current fern diversity. Based on molecular phylogenetic analyses of chloroplast DNA (psbA-trnH, trnG-trnR) and low-copy nuclear DNA (gapCp) sequences and flow cytometric analysis, we attempt to clarify the origin of putative Nephrolepis hybrids and cultivars. Our results confirm the presence of several hybrids, among which Nephrolepis ‘bostoniensis’ and Nephrolepis x hippocrepicis. Two widespread species, Nephrolepis biserrata and Nephrolepis cordifolia are revealed as the central species in the formation of these hybrids, with Nephrolepis brownii probably occasionally contributing as well. The C-values range indicates that all analysed Nephrolepis taxa are diploid except for Nephrolepis hirsutula, which is probably a tetraploid. All hybrids and cultivars are found to be diploid or homoploid hybrids. Additionally, our results suggest that Nephrolepis davallioides might also be a hybrid, possibly of multiple origins.