Diplazium zangnanense, a new species of the twinsorus-fern genus Diplazium (Athyriaceae) from Xizang Province, China

Diplazium zangnanense, a new species of Diplazium Sw. from Medog county, Xizang Autonomous Region, China, is described and illustrated. Morphological comparisons between this new species and similar ones (e.g., D. kawakamii, D. medogense, D. muricatum, D. multicaudatum, and D. spectabile, etc.) are provided. Molecular evidence shows that the new species is closely related to D. multicaudatum. The most distinctive characters of D. zangnanense are its decumbent to erect rhizomes, bicolorous scales with toothed margin on the stems, and oblong sori.

Methods
We combined all six chloroplast markers(atpA,atpB, matK , rps4-trnS IGS, trnL-F, matK ) in one dataset and analyzed them using the maximum likelihood (ML) and Bayesian inference (BI) methods. For ML and BI analyses, we used PartitionFinder v.2.1.1 (Lanfear et al., 2012) to determine the appropriate DNA substitution model according to the corrected Akaike information criterion (AICc). The ML analysis was conducted using IQ-Tree v.1.6 (Nguyen et al., 2014), with bootstrap values (BS) calculated based on 1,000 bootstrap replications. The BI analysis was performed in MrBayes v.3.2.6 (Ronquist et al., 2012) based on the same partitioning schemes and substitution model as indicated in the ML analysis. Four Markov Chain Monte Carlo (MCMC) chains were run, and every chain was generated for 3,000,000 generations with one cold chain and three hot chains. We sampled the cold chain every 1,000 generations. We combined the independent runs to obtain majority-rule consensus trees and to calculate posterior probabilities (PP).