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A new species, Didymodon imbricatus C. Feng & J. Kou, is described and illustrated from Nianzishan District, Heilongjiang Province, China. It is characterized mainly by short‐lanceolate to ovate‐lanceolate leaves with broadly acute to obtuse and strongly cucullate apex, leaf margins recurved throughout and bistratose in distal part, lamina red with KOH, costa ending below apex and usually spurred above midleaf, with guide cells in 2 layers below midleaf and without ventral stereids, and the presence of gemmae in the leaf axils. The new species is contrasted with similar species in the genus.

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It is characterized mainly by its ovate to ovate-lanceolate leaves appressed to weakly erect when dry, margins recurved from leaf base to apex, laminal cell superficial walls markedly thicker than the internal walls, laminal papillae present only on both sides of costa, short-excurrent costa, undifferentiated basal cells and differentiated perichaetial leaves. This species is compared with similar species and its ecology is discussed.

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.

Both papillae and mammillae are important structural characteristics for Pottiaceae classification, but these characters are diverse and their nomenclature is confused, hindering the classification of Pottiaceae. So, we selected representative species that cover all types of papillae and mammillae of Chinese Pottiaceae and observed and compared differences between them using light and scanning electronic microscopy. We corrected the chaotic descriptions of papillae of representative species, and have provided a uniform set of terms (“simple”, “forked”, “branched”, and “pedicellate”) to describe the shapes of papillae. In addition, we described how to quickly and accurately use papillae and mammillae to classify representative species in Chinese Pottiaceae.

A new species belonging to Didymodon sensu lato, Vinealobryum guangdongensis, is described and illustrated from Nanling National Forest Park of Guangdong, China. It is characterized by noteworthily thick‐walled cells of the cauline central cylinder, ovate‐lanceolate leaves that are appressed when dry, acuminate to acute leaf apices, leaf base abruptly broadened and quickly narrowed to the insertion, leaf margins recurved in proximal 2/3 to 3/4, short‐excurrent costa with 0–1 layer of ventral stereids, laminal cells with conical or elliptical papillae either over the lumina or over transverse walls, presence of gemmae in the leaf axils, and KOH laminal color reaction red to reddish orange. This new species is compared with the most similar species and its ecology is discussed.