Changbai Mountain, located in northeast China, is one of the areas with the most complete natural ecosystem preservation in China. A new species, Didymodon changbaiensis C.Feng, J.Kou, H.-X. Xiao & T.-T.Wu from north slope of Changbai Mountain in Jilin Province of China is described and illustrated. It is characterised by ovate or ovate-lanceolate leaves that are appressed when dry, acute leaf apex, lamina red or reddish-orange with KOH, unistratose lamina throughout, plane and unistratose leaf margins, percurrent costa with one layer of guide cells and without ventral stereids, upper and middle laminal cells with elliptical papillae over the transverse walls between two immediately adjacent cells and basal laminal cells not differentiated from the median cells. Our morphological analyses and molecular results, based on DNA sequences of ITS, rps4 and trnM-trnV, confirm that D. changbaiensis is revealed to be sister to 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, northeast China, phylogenetic analysis, taxonomy

Changbai Mountain National Reserve is located at the junction of three counties: Antu County, Fusong County and Changbai County in the southeast of Jilin Province, with a total area of 196,000 ha². It is one of the earliest national nature reserves established in China. The vertical height difference of the Nature Reserve is nearly 2000 m and the altitude is between 720 and 2691 m (Jia et al. 2020). From bottom to top, the landform can be clearly divided into three annular zones: lava platform, lava plateau and volcanic cone. The protected area belongs to the temperate humid monsoon climate, which is generally characterised by long and cold winters, short and cool summers, strong and dry winds in spring and foggy and cool autumns. The plants in the area belong to the flora of Changbai Mountain and the vegetation changes vertically with the altitude gradient. The vegetation in this area has obvious vertical zonal distribution due to the influence of climate and it is generally divided into four vertical vegetation zones. From the foot of the mountain to the top of the mountain are generally: broad-leaved Korean pine forest belt (below 1100 m), spruce fir forest belt (1100–1800 m), Yuehua forest belt (1800–2100 m) and alpine tundra belt (greater than 2100 m) (Ping et al. 2016). Due to the diverse characteristics of topography, climate and ecosystem, the area is rich in biodiversity resources. There are nine species of amphibians, 12 species of reptiles, 24 species of fish, 56 species of mammals, 230 species of birds and 1255 species of insects in the Reserve, respectively (Tang et al. 2011). In addition, there are 430 species of fungi, 200 species of lichens, 311 species of bryophyte, 78 species of ferns, 11 species of gymnosperms and at least 1325 species of neutrophils (Zhang et al. 2016).

Although the bryophyte flora of Changbai Mountain has been well studied, most of these studies were nearly twenty years ago (e.g. Koponen et al. 1983; Cao and Guo 2000; Cao et al. 2002; Guo et al. 2002). In the background of the recent revolution of genus Didymodon (Zander 2013; Zander 2019) which was split 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), a re-evaluation of Didymodon in China is being conducted by the authors (e.g. Feng et al. 2022a; Feng et al. 2022b). During a recent excursion in Changbai Mountain, many specimens have been collected. Amongst them, two samples of Didymodon s. lat. from stony habitats are different from species previously reported in the area (Li et al. 2001). They mostly resemble Didymodon tibeticus 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 combined length of ITS and cpDNA (rps4 and trnM-trnV) is 4622 bp. The position of the new species is different between the BI and ML phylogenetic trees and, thus, both of them are reserved. The topology, based on ML analyses, shows that the new species is sister to Didymodon daqingii J. Kou, R.H. Zander & C. Feng and they nested within the monophyletic group comprising Didymodon hengduanensis J.A. Jiménez, D.G. Long, Shevock & J. Guerra, D. icmadophilus (Schimp. ex Müll. Hal.) K. Saito, D. mesopapillosus J. Kou, X.-M. Shao & C. Feng, D. tibeticus and D. vulcanicus J.A.Jiménez, Hedd. & Frank Müll (Fig. 1). The BI tree was more similar to that of the ML tree, but with weakly-supported values (Fig. 2).

Figure 1. 

Maximum Likelihood tree inferred from concatenated ITS, rps4 and trnM-trnV datasets. Numbers indicate Maximum Likelihood bootstrap values. The numbers 234 and 188 show the sample of D. changbaiensis and an unknown species, respectively.

Figure 2. 

Phylogenetic relationships (50% majority consensus tree) from the Bayesian Inference of the concatenated ITS, rps4 and trnM-trnV datasets. Numbers indicate posterior probability from the BI analysis. The numbers 234 and 188 show the sample of D. changbaiensis and an unknown species, respectively.

Our molecular analyses reveal that the new species belongs to Didymodon s.str. Morphologically, the combination of characters: concave leaves, plane leaf margins, percurrent to excurrent costa, seldom papillose laminal cells, costa with quadrate or occasionally short-rectangular superficial adaxial cells and absence of costal adaxial stereid band also suggests the placement of the new species in the emended genus Didymodon s.str. Zander (1978, 1993, 2013). The new species is distinguished from all congeners by the following combination of diagnostic features: ovate or ovate-lanceolate leaves that are appressed when dry, acute leaf apex, lamina red or reddish-orange with KOH, unistratose lamina throughout, plane and unistratose leaf margins, percurrent costa with one layer of guide cells and without ventral stereids, upper and middle laminal cells with elliptical papillae over the transverse walls between two immediately adjacent cells and basal laminal cells not differentiated from the median cells.

The phylogenetic analyses support that the new species is closely related to D. daqingii, a species that was recently described from Inner Mongolia, China (Kou et al. 2019). They have similarity in quadrate or subquadrate ventral cells of costa in the upper middle part of the leaf, bulging costal ventral surface cells, transverse section of costa round at mid-leaf and costa without ventral stereids. However, D. daqingii differs from the new species by the long-lanceolate leaves, very fragile and bistratose leaf apices, distally bistratose and recurved leaf margins, costa with guide cells in 2–3 layers, laminal cells with 1–3 simple papillae per cell and yellow-green KOH laminal colour reaction.

There are five species that are related to the new species, based on our phylogenetic analysis. Amongst them, the new species is most similar to D. tibeticus, based on morphological characters. They share such distinctive characteristics as the shape of the leaves, lamina red or reddish-orange with KOH, unistratose lamina throughout, plane and unistratose leaf margins and percurrent costa. Nevertheless, D. tibeticus can be separated from the new species by the costa with a ventral costal pad of cells and 0–1 layer of ventral stereids, transverse section of costa flattened at mid-leaf and laminal cells with 1–2 simple or bifurcate papillae per cell. Other species, Didymodon hengduanensis J.A. Jiménez, D.G. Long, Shevock & J. Guerra, D. icmadophilus (Schimp. ex Müll. Hal.) K. Saito, D. mesopapillosus J. Kou, X.-M. Shao & C. Feng and D. vulcanicus J.A.Jiménez, Hedd. & Frank Müll. are distinguished from the new species by their recurved leaf margins and costa with ventral stereids.

Taxonomic treatment

 Didymodon changbaiensis J.Kou, C.Feng, H.-X.Xiao & T.-T.Wu, sp. nov.

Figs 3, 4 Chinese name: 长白山对齿藓

Type

China. Jilin Province: Changbai Mountain, 42°3'35.316"N, 128°3'51.516"E, on soil over rocks, elevation 1864 m, 2 September 2020, Jin Kou 20200902234 (holotype: NENU!; isotype: NMAC 20200902234!).

Diagnosis

It differs from the otherwise similar D. tibeticus in its costa without a ventral costal pad of cells and ventral stereids, transverse section of costa round at mid-leaf and laminal cells with elliptical papillae over the transverse walls between two immediately adjacent cells.

Description

Plants to 1 cm high, growing in dense turfs, brown-reddish below, green above. Stems erect, frequently branched, in transverse section rounded, central strand weakly differentiated, hyalodermis and sclerodermis absent; axillary hairs filiform, usually 3–4 cells long, with one brown basal cell and hyaline upper ones. Rhizoidal tubers absent. Leaves appressed when dry, erect when moist, ovate or ovate-triangular with a broad base, 0.85–1.3 × 0.43–0.65 mm, channelled ventrally in the upper part; lamina completely unistratose, reddish-orange in KOH; apex acuminate to acute, not cucullate; margins entire, plane, completely unistratose; costa 51.7–86.2 µm wide at base, percurrent to short-excurrent; ventral cells of costa in upper middle part of leaf quadrate or subquadrate, sparsely papillose; dorsal cells of costa in upper middle part of leaf quadrate or subquadrate, sparsely papillose; transverse section of costa round at mid-leaf; with 3–4 guide cells in one layer, absence of ventral stereids, 1–2 layers of dorsal stereids, without hydroids, ventral surface cells bulging, not forming a pad of a single layer of cells, papillose, dorsal surface cells papillose; upper and middle laminal cells subquadrate, hexagonal or shortly rectangular, 5.5–11.1 × 8.9–12.2 µm, dorsally with one low elliptical papilla over the transverse walls which reaches the two immediate cells; basal cells weakly differentiated, smooth, basal juxtacostal cells hexagonal or short-rectangular, 11.1–20 × 5.56–10 µm, evenly thick-walled; basal marginal cells oblate, 5.56–10 × 6.67–10 µm, with regular thickened transverse walls and thin longitudinal walls. Gemmae absent. Dioicous. Sporophyte unknown.

Figure 3. 

Didymodon changbaiensis A dry plants B moist plants C cross-section of stem D axillary hairs E leaves F leaf apex G upper part of costa (dorsal) H upper part of costa (ventral) I upper leaf margin, arrows shows the laminal cells with elliptical papillae over the transverse walls between two immediately adjacent cells. Photographed on 25 May 2022 by Chao Feng from the isotype.

Figure 4. 

Didymodon changbaiensis A, B median leaf cells, arrows show the laminal cells with elliptical papillae over the transverse walls between two immediately adjacent cells C basal juxtacostal cells D basal marginal cells E–J cross-sections of leaves, sequentially from apex to base. Photographed on 25 May 2022 by Chao Feng from the isotype.

Etymology

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

Habitat and distribution

The new species is currently known only from the type locality at the north slope of Changbai Mountain, Jinlin Province, China, growing on thin soil over rocks.

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 are very grateful to Dr Grzegorz J. Wolski of University of Lodz for his 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), Natural Science Foundation of Inner Mongolia (grant no. 2022MS03066) and the Innovative team of China’s Ministry of Education-Research on the sustainable use of grassland resources (IRT_17R59).