Didymodon Hedw., with approximately 140 species in the family Pottiaceae, is distributed nearly throughout the world, with the greatest diversity and important ecological functions in drought lands and alpine ecosystems. Several studies involving morphology, molecular systematics, and macro‐systematic analysis have addressed the infrageneric classification of Didymodon, but controversy over the position of the infrageneric and species classification remains due to its high degree of morphological variation in micro‐habitats and strong sensitivity to climate change at regional and global scale. To date, only a few phylogenetic studies have been conducted with an incomplete number of Didymodon species; further, there is no study published regarding the divergence time of Didymodon. Consequently, we conducted a comprehensive phylogenetic analysis of Didymodon species, sampling a total of 107 species, based on one nuclear (ITS) and five chloroplast DNA. Moreover, divergence time analysis was conducted to infer the age of origin and divergence of Didymodon species. Our results presented the largest scale phylogenetic relationship of Didymodon to date and resolved the phylogenetic status of some controversial taxa and the new species. The divergence time estimation showed that Didymodon species originated around the early Cretaceous, and the diversification was concentrated in the Cretaceous and Eocene. Paleoclimate and environmental change have a direct impact on the origin and divergence of Didymodon species by shaping their morphology, resource availability and ecological niche. Our study will help understand species origin and speciation of Didymodon as well as reflecting species adaptability and experience to historical events.

A new species, Didymodon sinicus C. Feng & J. Kou, is described and illustrated based on materials collected from Inner Mongolia, Yunnan and Tibet of China. It is characterized by ovate‐lanceolate to ovate‐triangular leaves that are erect to patent when wet, auriculate leaf base, acute leaves apices, distally bistratose leaf margins, the yellowish color in KOH, short‐excurrent costa with guide cells in 2–3 layers and without ventral stereids, and smooth laminal cells. A phylogenetic analysis based on DNA sequences of ITS, rps4, trnM‐trnV confirms D. sinicus as a sister to the clade of D. obtusus J. Kou, X.‐M. Shao & C. Feng and the new species belongs to the genus Didymodon s.str.

Both a complex topography and climate change have huge impacts on the distribution and genetic structure of extant species. Due to the lack of relevant molecular research, little is definitively known about the phylogeography of herbaceous plants in East Asia. Here we investigate the genetic diversity, population structure and historical population dynamics ofIris dichotomaPallas, a widespread perennial herbaceous species in northeastern and northern China. Twenty‐nine populations, totalling 297 individuals, were sampled throughout the Chinese distributional range ofI. dichotoma. The combined sequences of six chloroplast DNA fragments (petA‐psbE,rps18‐clpp,psbJ‐petA,trnD‐trnT,rps16andndhA) were used to identify 13 haplotypes, of which six were private ones restricted in a single population. Genetic differentiation amongI. dichotomapopulations, enabled us to infer potential refugia during the glacial period in the Yinshan Mountains–Yanshan Mountains, where high levels of haplotype and nucleotide diversity were detected. The results of a neutral test and mismatch distribution analysis both indicated thatI. dichotomaunderwent a recent population expansion. In East Asia, postglacial environmental and climatic changes appear to have promoted genetic diversification not only in better‐studied woody species, but also in herbaceous ones likeI. dichotoma. Future studies of more herbaceous plant species are needed to obtain better insight into how modern temperate biodiversity has developed in East Asia.

Didymodon heilongjiangensis is described as a new species from Nianzishan District, Heilongjiang Province, China. It is mainly characterized by triangular to ovate‐lanceolate leaves that are erect to erect‐patent when moist, acute leaf apices, leaf margins recurved to near leaf apex, yellowish color in KOH, percurrent to short‐excurrent costa that is widened toward apex, laminal cells with low papillae over the transverse walls, which reach the two adjacent cells, and marginal basal cells with thickened transverse walls. A phylogenetic analysis based on DNA sequences of ITS, rps4, trnM‐trnV confirms that D. heilongjiangensis belongs to the genus Didymodon s.str. The new species is fully illustrated and its affinities are discussed in detail.