The current circumscription of Polystichum Roth (Dryopteridaceae) goes back to Ching’s removal of Cyrtogonellum Ching and Cyrtomidictyum Ching from Polystichum and allies. As one of the most species-rich fern genera, Polystichum Roth (Dryopteridaceae) is very nearly a cosmopolitan genus with its natural distribution in every continent except in Antarctica. Its highest species diversity, however, is undoubtedly found in Asia, especially in Southwest China and adjacent regions. Estimates of the number of species of Polystichum worldwide have ranged from at least 200, slightly more than 225, to ca. 300. The most recent explorations in the limestone areas in southern China demonstrate that there are far more species in the genus than had been thought. The application of molecular phylogenetics in the study of Polystichum also allows to identify numerous cryptic or semi-cryptic species of Polystichum previously unknown to science. The current estimate of species number of Polystichum in new circumscription is about 450, which makes Polystichum probably the fourth largest fern genus in the world..In this project, I will sample up to 400 accessions of Polystichum and allies genera. Both chloroplast genes (rbcL, rps4-trnS, trnL-F) and nuclear genes, gapCp and others, will be sampled to reconstruct a phylogeny of Polystichum sensu lato. Most importantly, I plan to develop nuclear markers. If successful, the results of nuclear markers should have long and lasting impact on not only on the evolution of one of the largest genera in ferns but also the phylogeny and evoltion of ferns in general. Most notably, a phylogeny of a large genus in vascular plants with over 400 accessions (samples) sequenced has never been published in the whole world before. This is going to be the first of its kind and will be significant work in the plant systematics community for many years to come.