From the Himalayan region or the Malay Archipelago: Molecular dating to trace the origin of a fern genus Phymatopteris (Polypodiaceae)

Phymatopteris Pic. Serm., a derived polypodiaceous fern, is one of the many fern genera that still suffer from nomenclatural confusion. Its generic circumscription and phylogenetic relationships with other selligueoid ferns have been controversial, and its geographic origin, whether in the Himalayan region of continental Asia or in Malay Archipelago, is still unknown. A phylogeny of all selligueoid ferns based on 4 cpDNA (rbcL, trnL-F, rps4 and rps4-trnS) regions indicates that Phymatopteris is not monophyletic. Phymatopteris species are distributed in 5 well-supported clades that can be distinguished with frond-shape and frond-margin characters. All early-divergent species are from the Malaysian Archipelago, while the remaining species are all from the Himalayan region and form a recently diverged group that is largely unresolved, most likely having resulted from an explosive radiation. Divergence-time estimation suggests that the first diversification of selligueoid ferns occurred at ca. 27 Ma in the Malaysian Archipelago, followed by migration into the Himalayan region around 20 Ma. The radiation of the Himalayan species occurred mostly within the last 20 million years, within the period of recent major uplifts of the Qinghai-Tibetan Plateau (between the early Miocene and the Pleistocene) and late-Cenozoic global cooling. Our evidence leads us to propose that the Malaysian Archipelago is the ancestral area for Phymatopteris.