Phylogenetic relationships of Neotropical lady ferns (Athyriaceae), with a description of Ephemeropteris, gen. nov.

We carried out a molecular phylogenetic analysis of Neotropical lady ferns (Athyrium s.str. and Anisocampium) using five plastid markers. We found two major results. First, three Neotropical species (Anisocampium skinneri, Athyrium palmense, A. tejeroi) formed a clade, and this clade was sister to the rest of Athyrium. The three members of this clade differ from Athyrium s.l. by creeping rhizomes with internodes 1-2 mm long, and rhizome apices that protrude beyond the current season's cluster of leaves. Also, the leaves are distichously arranged, lack trophopods, have petiole bases broadly U-shaped in transverse section, and bear thin, membranous laminae. We recognize this clade as a new genus, Ephemeropteris, and provide three new combinations: E. palmensis, E. skinneri, and E. tejeroi. The name of the new genus is derived from the seasonal production of its leaves, which are produced during the wet season and die back (i.e., are ephemeral) at the beginning of the dry season. Ephemeropteris is largely restricted to the Pacific side of Central America, a region that exhibits a marked dry season from November to May. We provide a key to the seven genera (including Ephemeropteris) we now recognize in the Athyriaceae, and a taxonomic treatment of the three species of Ephemeropteris. The treatment includes descriptions, illustrations, nomenclatural data, specimens cited, and a dot-distribution map. Our second major result from the phylogenetic analysis is that the remaining three Neotropical species of Athyrium s.str. are polyphyletic. One of our seven samples was resolved in the A. filix-femina clade (sect. Athyrium), to which all species of Neotropical Athyrium were previously assumed to belong to. Our six other samples of Neotropical Athyrium were resolved in A. sect. Mackinnoniana, previously construed as entirely Asian.