Phylogeny of the fern subfamily Pteridoideae (Pteridaceae; Pteridophyta), with the description of a new genus: Gastoniella.

As the second most genera-rich fern family, Pteridaceae contain more than 1000 species contributing to ca. 10% of extant leptosporangiate fern diversity. The subfamily Pteridoideae is one of the five subfamilies often recognized. The circumscription of Pteridoideae has not been clear. A large number of species have not yet been included in any molecular analyses before. In this study, DNA sequences of six plastid loci of 154 accessions representing ca. 87 species in 14 genera of Pteridaceae subfam. Pteridoideae and four accessions representing two species in subfam. Parkerioideae and one species of subfam. Adiantoideae as outgroups were used to infer a phylogeny using maximum likelihood and maximum parsimony. Our analyses show that (1) Pteridoideae is monophyletic and the newly defined subfamily is composed of 14 genera including a newly described genus; (2) Pteridoideae is resolved into four strongly supported monophyletic clades: the Pteris clade, the Actiniopteris+Onychium clade, the JAPSTT clade, and the GAPCC clade, these being supported by not only molecular data but also morphological features and distribution information; (3) Onychium is confirmed as monophyletic and accessions of Onychium are resolved into two strongly supported clades, the O. cryptogrammoides clade and the O. siliculosum clade; and (4) Accessions of the traditionally defined Anogramma are resolved as paraphyletic in relation to Cerosora, Cosentinica, and Pityrogramma. Three species traditionally treated in Anogramma are in fact more closely related to Cerosora and Pityrogramma than they are to Anogramma. Gastoniella Li Bing Zhang & Liang Zhang, gen. nov. is described to accommodate these species and three new combinations are provided. Three currently known species of Gastoniella are distributed in the Ascension Island in South Atlantic Ocean, central Mexico, and tropical America, respectively. The new genus is distinct from Anogramma s.s. in having ultimate segments linear not obviously broadening toward the upper portion.