Phylogenetic analyses place the Australian monotypic Revwattsia in Dryopteris (Dryopteridaceae)

Revwattsia fragilis (Watts) D.L. Jones (Dryopteridaceae), originally described as a Polystichum Roth by the pioneer Australian botanist Reverend W.W. Watts in 1914, is a rare epiphytic fern endemic to northeastern Queensland, Australia. Known from only a few populations, it is restricted to tropical rainforests in the Atherton Tablelands. We used the cpDNA markers psbA-trnH, rbcL, rbcL-accD, rps4-trnS, trnG-trnR, trnL-trnF, and trnP-petG to infer the relationships of Revwattsia fragilis within Dryopteridaceae. Based on our molecular analysis, we were able to reject Watts's 1914 hypothesis of a close relationship to Polystichum. Its closest allies are a suite of Asian Dryopteris Adans. species including Dryopteris labordei, Dryopteris gymnosora, Dryopteris erythrosora and Dryopteris cystolepidota; maintaining Revwattsia renders Dryopteris paraphyletic. The epiphytic habit and distinctive long-creeping rhizome of Revwattsia appear to be autapomorphies and do not warrant its generic status. In the course of our investigation we confirmed that polyphyly of Dryopteris is also sustained by the inclusion of Acrorumohra (H.Itô) H.Itô, Acrophorus C.Presl, Arachniodes Blume, Diacalpe Blume, Dryopsis Holttum & P.J.Edwards, and Peranema D.Don. The epithet fragilis is occupied in Dryopteris, therefore we provide the name Dryopteris wattsiinom. nov. to accommodate Revwattsia fragilis in Dryopteris.