Species delimitation and molecular diagnosis of Cyrtomium yamomotoi (Dryopteridaceae)

The genus Cyrtomium is one of the most taxonomically challenging groups, which comprises about 40 taxa globally. Cyrtomium yamamotoi is a great example showing the taxonomic difficulties in the genus. The plant was first described as a variety (C. fortunei var. intermedium), thereafter the rank was moved to a species by Tagawa in 1938. Cyrtomium yamamotoi and its related taxa including five varieties of C. fortunei are triploid apogamous taxa with high morphological variabilities. The substantial morphological variations likely resulted from hybrid origins leading to various taxonomic complications. To determine the species boundary between C. yamamotoi and the C. fortunei complex, we inferred the phylogenetic relationships among the complex and the five related taxa including C. falcatum using the two widely used cpDNA regions, rbcL and psbA-trnH IGS. We also carefully examined the nomenclatural histories of eleven Cyrtomium taxa (five taxa of C. fortunei complex and six related taxa) and the key morphological characters. According to our analysis, Cyrtomium yamamotoi is likely an independent species as the phylogenetic results revealed that C. yamamotoi was separated from the C. fortunei complex while all members of C. fortunei complex formed a monophyletic clade.