Inner Mongolia steppe is one of the suitable habitats for Didymodon species and a new species, Didymodon manhanensis C. Feng & J. Kou from Manhan Mountain in semi-arid region in Inner Mongolia, China is described and illustrated. It is characterised by leaves incurved and slightly twisted when dry, spreading when moist, narrowly lanceolate from an ovate base; subulate and fragile leaf apices; distally bistratose leaf margins that are recurved in proximal 2/3–3/4; excurrent costa with guide cells in 2–3 layers and without ventral stereids; smooth laminal cells and red KOH laminal colour reaction. Our morphological analyses and molecular results, based on DNA sequences of ITS, rps4 and trnM-trnV, confirm that D. manhanensis belongs to a group that includes D. obtusus J. Kou, X.-M. Shao & C. Feng and D. daqingii J. Kou, R.H. Zander & C. Feng. This new species is compared with similar species and its phylogenetic position and ecology are discussed.

Asia, Manhan Mountain, phylogenetic analysis, taxonomy

Inner Mongolia, situated in Inner Eurasia, is located in the northern part of China and presents a strip distribution from the northeast to the west. The district habitats are temperate continental monsoon climate. The annual mean temperature is 8 °C, which increases from east to west and the annual precipitation is 35–530 mm, which decreases from southeast to northwest (Miao 2017). The area of grassland accounts for 60% of the whole Inner Mongolia and more than one-quarter of the total area of grassland in China. The grassland in Inner Mongolia is divided into three types: meadow steppe formed by, for example, Stipa baicalensis Roshev, Leymus chinensis (Trin.) Tzvelev; typical steppe formed by, for example, Stipa grandis P. Smirn., Stipa krylovii Roshev, Leymus chinensis (Trin.) Tzvelev and desert steppe formed by, for example, Stipa klemenzii Roshev, Stipa glareosa P.A. Smirn., Stipa breviflora Griseb (Hua et al. 2021). The main vegetation types of the steppes present distinct zonal features (Wu et al. 2005). The Inner Mongolia steppe is a suitable habitat for the Didymoodn Hedw. species and several new species were recently discovered (e.g. Kou et al. 2016a; Kou et al. 2019; Feng et al. 2022).

The taxonomy of genus Didymodon is complicated, involving the differentiation from related genera, such as Barbula Hedw. and the circumscriptions of its infrageneric sections (Zander 1993; Zander 2007; Zhang et al. in press). A recent important event associated with Didymodon s. lat. was the split of the genus into seven smaller genera: Aithobryum R.H. Zander, Didymodon s. str., Exobryum R.H. Zander, Fuscobryum R.H. Zander, Geheebia Schimp., Trichostomopsis Card. and Vinealobryum R.H. Zander, based on macro-evolutionary analysis and the dissilient genus concept applied (Zander 2013; Zander 2019). Although initially this revolutionary concept was considered unnecessary or unsupported (Blockeel and Kučera 2019), it has later been supported by molecular phylogenetic data, but with some alterations (Jiménez et al. 2022; Zhang et al. in press) and has gained acceptance by some other authors (e.g. Kou and Feng 2018; Osman et al. 2021; Feng et al. 2022). During our continuous investigations of xerophilic mosses, especially Pottiaceae Hampe, in China (e.g. Feng et al. 2016a, b; Kou et al. 2016b, 2018, 2019; Kou and Feng 2018), many specimens have been collected from different provinces. Amongst them, two samples collected from Manhan Mountain in Inner Mongolia of Didymodon s. lat. from stony habitats are different from species previously reported in the area (Li et al. 2001). They mostly resemble Didymodon obtusus J. Kou, X.-M. Shao & C. Feng. To clarify their taxonomic identity, we conducted phylogenetic analysis and confirm that these samples belong to the genus Didymodon s. str. (Zander 2013), but do not match with any species known in the genus. Here, we describe this unknown moss as a new species.

The chloroplast (cp) and ITS alignments comprised 1313 and 1364 nucleotide sites, respectively. The BI and ML phylogenetic trees have a consistent topology, although there are different levels of support depending on the method. Hence, only the topologies with branch lengths from the BI trees are presented, with added support from the ML method on the respective trees (Figs 3–4). Although the inference from analysed chloroplast regions (Fig. 3) and the ITS (Fig. 4) agrees in most aspects, the position of the new species is different between the two above phylogenetic trees and, thus, both of them are reserved. The topology of the ITS dataset shows that D. manhanensis is nested within the monophyletic group comprising Didymodon epapillatus J. Kou, X.-M. Shao & C. Feng, Didymodon mongolicus D.-P. Zhao & T.-R. Zhang, Didymodon validus Limpr., Didymodon wisselii (Dixon) D.H. Norris & T.J. Kop. and Vinealobryum guangdongensis C. Feng & J. Kou and is sister to D. obtusus, but with weakly-supported values. In the combined plastid dataset, D. manhanensis is nested within the group including Didymodon cordatus Jur. and is sister to D. daqingii and Didymodon anserinocapitatus (X.J. Li) R.H. Zander, with well-supported values.

As indicated by Zander (1993), Didymodon s. lat. is heterogeneous and could be profitably split. In our phylogenetic analyses, this genus is polyphyletic and its species can be classified within several well-supported monophyletic clades, which correspond to other phylogenetic studies of the genus (Feng et al. 2022; Jiménez et al. 2022; Zhang et al. in press). Our results reveal a close relationship between D. manhanensis and two recently-described species in China: D. daqingii and D. obtusus. Although the latter two species were considered identical by Sollman et al. (2020), they are not closely related in our phylogenetic analyses, based on both ITS and chloroplast data.

Didymodon manhanensis is distinguished from all congeners by the following combination of diagnostic features: leaves incurved and slightly twisted when dry, spreading when moist, narrowly lanceolate from an ovate base; subulate and fragile leaf apices; distally bistratose leaf margins that are recurved in proximal 2/3–3/4; costal guide cells in 2–3 layers and without ventral stereids, smooth laminal cells and red KOH laminal colour reaction. This combination of characters suggests the placement of D. manhanensis in the sect. Didymodon (Zander 1978, 1993, 1998). Following the recent revolutionary work on the genus Didymodon s. lat. by Zander (2013, 2019), morphologically, it belongs in the amended genus Didymodon s. str. Its systematic position in Didymodon s. str. was also confirmed by our phylogenetic analyses, based on both ITS and chloroplast data.

Chloroplast data support that D. manhanensis is closely related to D. cordatus and sister to both D. daqingii and D. anserinocapitatus. However, D. manhanensis differs morphologically from D. cordatus by the costa with guide cells in 2–3 layers and without ventral stereids and smooth laminal cells. It differs from D. daqingii by the leaves that are narrowly lanceolate from an ovate base, smooth laminal cells and red KOH laminal colour reaction; it differs from D. anserinocapitatus by the distally bistratose leaf margins and lack of swollen and deciduous leaf apex (Zander 2007). In the ITS analyses, there is successive branching of clades, including D. obtusus J. Kou, X.-M. Shao & C. Feng, D. manhanensis, D. epapillatus J. Kou, X.-M. Shao & C. Feng, D. mongolicus D.-P. Zhao & T.-R. Zhang, D. validus Limpr., Vinealobryum guangdongensis C. Feng & J. Kou and D. wisselii (Dixon) D.H. Norris & T.J. Kop. Amongst these species, D. manhanensis is most similar to D. obtusus, a species that was recently described from Tibet in China (Kou et al. 2018), but the former can be distinguished from the latter by its narrowly lanceolate leaves from an ovate base and spreading when moist, subulate and somewhat fragile leaf apex and unistratose distal lamina.

There are three species distributed in China that have excurrent costa and smooth laminal cells may be confused with the new species. Didymodon ditrichoides (Broth.) X.-J. Li & S. He, a species known from North American, Asia (China) and the Atlantic Islands (Iceland) (Li et al. 2001; Zander 2007), differs from the new species by the unistratose leaf margins, costa with 1–2 layers of guide cells and with 0–1 layer of ventral stereids and yellowish KOH laminal colour reaction (Zander 2007). Didymodon validus Limpr. can be separated from D. manhanensis by the twisted and incurved leaves when dry, unistratose leaf margins, costa with 1 layer of guide cells and with 1–3 layers of ventral stereids and yellowish-green KOH laminal colour reaction (Shuayib et al. 2017).

The lanceolate to long-lanceolate leaves with a widely ovate base, distally bistratose leaf margins, excurrent costa and epapillose laminal cells are likewise found in Didymodon ochyrarum J.A.Jiménez & M.J.Cano, a species described from tropical South America (Jiménez and Cano 2019), which may be confused with the new species. However, D. ochyrarum can be separated from D. manhanensis by its plane leaf margins, marginal basal cells running up the margin forming a distinctly differentiated area of transversely thick-walled cells and yellowish KOH laminal colour reaction.

Taxonomic treatment

 Didymodon manhanensis C. Feng & J. Kou, sp. nov.

Figs 1, 2 Chinese name: 蛮汉山对齿藓

Type

China. Inner Mongolia: Ulanqab City, Manhan Mountain, 40°39'19.2931"N, 112°19'36.3792"E, on soil under the grass, elevation 1417 m, 20 June 2016, Chao Feng 2016060162 (holotype: NMAC!; isotype: MO!).

Diagnosis

It is distinguished from all congeners by the following combination of diagnostic features: leaves incurved and slightly twisted when dry, spreading when moist, narrowly lanceolate from an ovate base; subulate and fragile leaf apices; distally bistratose leaf margins that are recurved in proximal 2/3–3/4; costal guide cells in 2–3 layers and without ventral stereids, smooth laminal cells and red KOH laminal colour reaction.

Description

Plants medium, growing in turfs, green-blackish distally, brown-blackish proximally. Stems very seldom branched, 0.8–1.6 cm in length, not papillose, transverse section rounded to rounded-pentagonal, central strand developed, sclerodermis present, hyalodermis absent; axillary hairs filiform, of 4–8 hyaline cells, the basal cell brown. Leaves crowded on stem, incurved and slightly twisted when dry, spreading when moist, narrowly lanceolate from an ovate base, constricted just above the base, 1.3–2.3 × 0.43–0.55 mm, distal lamina narrowly channelled ventrally; margins plane distally, recurved in proximal 2/3–3/4 of leaf, entire, distal margins bistratose; apex subulate, somewhat fragile; leaf base ovate, not sheathing, not decurrent; costa stout, tapering distally, 57.5–75 µm wide at base, excurrent as a long, thick subula, not spurred, ventral cells of costa in upper middle part of leaf quadrate or subquadrate, smooth, 4 rows of cells across costa ventrally at mid-leaf, dorsal cells of costa in upper middle part of leaf quadrate or subquadrate, smooth, transverse section semicircular to nearly rounded, epidermis present adaxially and abaxially, not or weakly bulging, ventral stereids absent, guide cells 10–16 in 2–3 layers, 2–4 layers of dorsal stereids, reniform or crescent-shaped, without hydroids; upper laminal cells quadrate to rhombic, usually with angular lumens, 7.5–10 × 5–10 µm, smooth, slightly thick-walled, weakly convex on both surfaces, distal lamina unistratose, basal cells weakly differentiated juxtacostally, rectangular, 12.5–37.5 × 5–7.5 µm, thin-walled, smooth; basal marginal cells subquadrate or quadrate, 5–8.75 × 6.25–7.5 µm, with weakly-thickened walls, smooth. Gemmae absent. Dioicous. Sporophytes unknown. KOH laminal colour reaction red.

Additional specimens examined

China Inner Mongolia: Ulanqab City, Manhan Mountain, on soil under the grass, 20 June 2016, Chao Feng 2016060176 (NMAC).

Etymology

The specific epithet refers to Manhan Mountain, the type locality.

Habitat and distribution

Manhan Mountain is situated in Liangcheng County in the southern section of the Yinshan Mountains in the middle of Inner Mongolia, with an average altitude of approximately 1500 m (Huang et al. 2014). Its soil types are mainly leaching grey, cinnamonic soil (Lyu et al. 2012). The vegetation on Manhan Mountain is typical forest shrub vegetation, including natural forest that consists of Betula platyphylla Sukaczev and Populus davidiana Dode, plantation that consists of Larix principis-rupprechtii Mayr and Pinus sylvestris var. mongolica Litv., natural shrubs that consists of Ostryopsis davidiana Decne., Spiraea salicifolia L. and Rosa davurica Pall. and the herbaceous plants including Stipa bungeana Trin., Cleistogenes squarrosa (Trin.) Keng, Lespedeza bicolor Turcz., Carex spp. and Leymus chinensis (Trin.) Tzvelev (Zhang et al. 2017; Li et al. 2021). Didymodon manhanensis is currently known only from the type locality at the foot of the Manhan Mountain, north-western Liangcheng County, Inner Mongolia, China, growing on soil under the grass.

Figure 1. 

Didymodon manhanensis A dry plants B moist plants C cross-section of stem D leaves E leaf apex F upper part of costa (dorsal) G upper part of costa (ventral) H axillary hairs. Photographed on 21 November 2021 by Chao Feng from the holotype (NMAC!).

Figure 2. 

Didymodon manhanensis A median leaf cells B basal juxtacostal cells C basal marginal cells; D–H cross-sections of leaves, sequentially from apex to base. Photographed on 21 November 2021 by Chao Feng from the holotype (NMAC!).

Figure 3. 

Phylogenetic relationships (50% majority consensus tree) from the Bayesian Inference of the concatenated rps4 and trnM-trnV datasets. Numbers above branches indicate posterior probability from the BI analysis, followed by bootstrap values for the ML analysis.

Figure 4. 

Phylogenetic relationships (50% majority consensus tree) from the Bayesian Inference on the ITS dataset. Numbers above branches indicate posterior probability from the BI analysis, followed by bootstrap values for the ML analysis.

Sincerest thanks are given to Dr Richard H. Zander, Missouri Botanical Garden, for his consistent help during the authors’ study of the Pottiaceae in China and for his valuable comments on the manuscript. We really appreciate Dr Jan Kučera, University of south Bohemia, for providing many valuable suggestions on the molecular experiment and help to obtain the sequences of D. daqingii and D. obtusus. We are very grateful to Dr Matt von Konrat of the Field Museum, Dr Grzegorz J. Wolski of University of Lodz and one anonymous reviewer for their constructive criticisms. This work was supported by the Natural Science Foundation of China (grant no. 42001045, 32060051, 31660051), Shenzhen Key Laboratory of Southern Subtropical Plant Diversity (grant no. 99203030) and the Innovative team of China’s Ministry of Education-Research on the sustainable use of grassland resources (IRT_17R59).