Didymochlaenaceae: A new fern family of eupolypods I (Polypodiales)

The pantropical monospecific fern genus Didymochlaena had long been placed in the family Dryopteridaceae before the advent of molecular phylogenetics. Recent molecular studies confirmed that it is a member of eupolypods I, but its familial placement has been controversial. It has been resolved using molecular data either as a member of Hypodematiaceae or as sister to the rest of eupolypods I. In the present study we performed phylogenetic analyses (MP, ML, BI) based on DNA data from five plastid loci (atpA, rbcL, rps4-trnS, trnL, trnL-F) of 88 accessions representing 79 species in 20 genera of all 9 families currently recognized in eupolypods I as ingroup and 5 species from 3 families of eupolypods II as outgroups. Our analyses resolved Didymochlaena as sister to the rest of eupolypods I with strong support. The results of an analysis of nuclear 18S data available from GenBank did not contradict those based on plastid data. This resolution is consistent with its sorus/indusium shape and a previous phylogenetic analysis based on both plastid and nuclear loci. Sorus shape, spore characters, and chromosome number previously used to place the genus in Dryopteridaceae are in fact not synapomorphies of the family. Our study clearly showed that the family Didymochlaenaceae should be recognized and we hereby validate this name previously proposed by Ching.