Phylogenetic Positions of the Enigmatic Asiatic Fern Genera Diplaziopsis and Rhachidosorus from Analyses of Four Plastid Genes

Nucleotide sequences from four plastid genes (rbcL, atpB, atpA, rps4) were used to infer relationships of Diplaziopsis and Rhachidosorus. The phylogenetic positions of these two Asian fern genera have been debated, and neither had been included in the most recent global molecular systematic studies of ferns. Our four plastid gene sequence analyses supported a sister relationship between Diplaziopsis, Rhachidosorus and the North American Homalosorus, the monophyletic group of the newly-examined genera is an early diverging lineage of Woodsiaceae, and far away from athyrioid ferns. The inferred relationships of Diplaziopsis and Rhachidosorus are not consistent with most recent treatments, while, some synapomorphic characteristics are shared with these two genera. Further studies on more morphological characters and gametophytes of these two genera are needed to test these relationship hypotheses.