The family Pottiaceae is notoriously difficult taxonomically. Many of its members are small, morphologically reduced plants whose features have been shaped by convergent evolution in response to stressful environments, which can blur the boundaries between species. Molecular studies have further complicated matters by revealing that some traditionally recognized subfamilial and generic relationships within the family require cautious interpretation. Yet the ecological importance of these mosses is hard to overstate. Most Pottiaceae species are desiccation-tolerant, capable of recovering rapidly after rehydration, and they thrive in soil crusts, rock surfaces, gravel slopes, and disturbed open substrates. These traits make them especially relevant in Mongolia, where aridity, strong solar radiation, wind abrasion, and episodic water availability act as powerful ecological filters on the flora.

Bryological exploration on the Mongolian Plateau began in the mid-nineteenth century, when foreign missionaries and experts collected plants that included only scattered moss specimens. Systematic study of Mongolian bryophytes did not begin until the 1970s, when Abramova and Tsegmed surveyed major mountain systems such as the Khangai, Khentii, and Mongolian Altai between 1976 and 1994, publishing foundational accounts. Tsegmed provided the first national checklist in 2001, listing 27 genera and 79 species of Pottiaceae. A multinational expedition to the Gobi Altai in 2004 documented 44 species in 17 genera, and the most comprehensive national treatment, the Moss Flora of Mongolia published in 2010, recognized 24 genera and 81 taxa. Subsequent collecting has steadily added new records, underscoring that the national list remains dynamic and in need of periodic, voucher-based updating under current taxonomic concepts.

To build the revised checklist, the researchers analyzed specimens from the Herbarium of Inner Mongolia University, the Herbarium of the Botanic Garden and Research Institute, and the Herbarium of the Missouri Botanical Garden, alongside published literature. Records were included only if they offered reliable taxonomic evidence, such as a voucher specimen or published identification, and specified locality information to at least the province level. Administrative names were standardized using a controlled vocabulary, spelling variants and diacritics were corrected, and duplicate entries representing the same taxon in the same sum were merged so that each accepted taxon contributed at most one sum-level occurrence per administrative unit. To avoid artificially inflating species counts, the team used a species-unit approach in which a province or sum with records of only one variety of a species was treated as harboring the parent species for richness calculations, while the infraspecific name was retained in the checklist for taxonomic detail.

The resulting picture of taxonomic diversity is strongly long-tailed, with a few large genera dominating the flora. Didymodon is by far the most species-rich genus, with 27 species and two varieties, representing 29.3 percent of all taxa. Syntrichia follows with 12 species and one variety, and Tortula with 11 species, while Bryoerythrophyllum contributes six species. The remaining 22 genera contain only one to five taxa each. The 26 genera are arranged into four subfamilies: Timmielloideae with a single genus, Trichostomoideae with five, and Barbuloideae and Pottioideae with ten each. The authors retained a morphology-based framework for generic circumscription, keeping Timmiella within Pottiaceae even though molecular phylogenies have proposed segregating it into a separate family, in order to maintain consistency with the principal floristic treatments used for specimen identification.

Geographically, the richest provinces are Khövsgöl with 53 species, Govi-Altai with 48, and Khovd with 45, followed by Bayankhongor and Töv with 40 and 36 species respectively. But the study also reveals a striking pattern of documentary unevenness. Sampling intensity, measured as the number of verified occurrence records, varies enormously among provinces, and observed richness tracks collecting effort remarkably closely: the correlation between the two is exceptionally strong, with a Pearson correlation coefficient of 0.961. Provinces such as Darkhan-Uul and Dundgovi are represented by very few verified records, and Orkhon and Govisumber have no verified sum-level records at all in the new database. At the sum level, the median richness is just 4.0 species, and 46 of the 160 sums contain only a single species. The richest sums are Renchinlkhümbe in Khövsgöl with 40 species, Bulgan in Khovd with 30, and Bogd in Bayankhongor, also with 30.

Occupancy patterns are strongly right-skewed at both provincial and sum levels. Nineteen species, or 20.4 percent of the flora, are found in only one province, and 23 species occur in just two or three. At the finer scale, 18 species are known from a single sum. Only a small subset of taxa is widespread, occurring in eight or more provinces. The most ubiquitous species are Bryoerythrophyllum recurvirostrum, recorded from 20 provinces and 83 sums, and Syntrichia ruralis, found in 18 provinces and 76 sums, both consistent with their broad ecological tolerance and frequent occurrence in open, disturbed, and drought-prone habitats. The authors caution that low occupancy in specimen-based datasets requires careful interpretation: a taxon recorded from a single province may be genuinely restricted, or it may simply reflect limited collection effort or the difficulty of detecting small, ephemeral, or morphologically variable plants.

The revision also reshuffles the national inventory itself. The update adds one genus, Pseudosymblepharis, and 20 taxa new to Mongolia, comprising 16 species and four varieties. Among the newly recorded species are Anoectangium aestivum, several Bryoerythrophyllum species including B. sollmanianum, Didymodon rivicola, Molendoa hornschuchiana, Oxystegus daldinianus, Pseudosymblepharis angustata, Stegonia pilifera, several Syntrichia taxa including S. calcicola and S. handelii, Timmiella crassinervis, Tortula capillaris, and two Weissia species. Each new record is anchored to examined specimens with full locality and collector details. Conversely, nine previously reported taxa were excluded from the Mongolian flora after critical reassessment, including Bryoerythrophyllum alpigenum, Pseudocrossidium revolutum, Syntrichia princeps, and Timmiella anomala, while three further names, among them Didymodon luridus, remain doubtful pending voucher confirmation.

Compared with the 2010 monograph, which recognized 24 genera and 81 taxa, the new checklist records 26 genera and 99 taxa, a substantial expansion driven by both new fieldwork and the reconciliation of synonyms and misapplied names with current taxonomic concepts. The authors emphasize that the database was assembled as a reproducible occurrence synthesis rather than a repeated collection-event dataset, so it is best used to identify survey gaps rather than for formal beta-diversity comparisons among provinces. They recommend that future work reconstruct collection-event data and apply species accumulation curves or other coverage-based approaches to determine how much additional sampling each province requires.

Beyond its administrative summaries, the checklist points to a broader environmental mosaic likely to underlie Pottiaceae diversity across Mongolia. Northern and central mountainous regions, especially around Khövsgöl and the Khangai range, combine elevational heterogeneity, contrasting slope exposures, rocky substrates, and locally buffered moisture, creating microsites for both xerophytic and montane taxa. The Gobi and drier steppe regions probably favor a different subset of species adapted to strong aridity and episodic water availability, with diversity structured by the fine-scale availability of exposed soil, gravel, rock crevices, and temporary moisture-retaining microsites. The western mountains, including the Mongolian Altai, compress multiple habitat types into small areas, potentially promoting local coexistence of cold-desert, steppe, and montane elements. The authors stress that these biogeographic interpretations should be treated as working hypotheses, since collecting intensity remains highly uneven, but the checklist now provides the standardized, voucher-anchored baseline needed to target future field surveys, integrative taxonomic revisions, biodiversity inventories, and conservation assessments across Mongolia and adjacent regions of Central Asia.

Subject of Research: Taxonomic revision and distribution of the moss family Pottiaceae in Mongolia

Article Title: A revised checklist of Pottiaceae ( Bryophyta ) in Mongolia

Article References: Enkhjargal, E., Feng, Q., Qi, Q., & Zhao, D. (2026). A revised checklist of Pottiaceae (Bryophyta) in Mongolia. PhytoKeys, 275, 191-208. https://doi.org/10.3897/phytokeys.275.197551

Image Credits: AI Generated

DOI: 10.3897/phytokeys.275.197551

Keywords: Pottiaceae, mosses, bryophytes, Mongolia, checklist, biodiversity, taxonomy, herbarium specimens, drylands, species occupancy, biogeography, PhytoKeys