Afonina, O.M., O.I. Kuznetsova & E.A. Ignatova. 2022. A revision of the Didymodon perobtusus group (Pottiaceae, Bryophyta) in Russia

Arctoa (2022) 31: 191–204

doi: 10.15298/arctoa.31.21

Morphological and molecular phylogenetic studies of two closely related species of Didymodon, D. perobtusus and D. subandreaeoides were conducted based on collections from Russia. Nuclear ITS based phylogenetic tree found D. perobtusus in a maximally supported terminal clade, albeit nested in a grade of D. subandreaeoides.The presence of D. perobtusus in the Caucasus, Subpolar Urals, Taimyr, Yakutia and Sakhalin Island was not confirmed; thus, its distribution in the country is restricted to southern Siberia, from the Baikal Lake area to the Altai Mts, with one disjunct locality on the eastern macroslope of the Polar Urals. In contrast, D. subandreaeoides, which was previously recorded from two localities in Russia, appeared to have wider distribution in Siberia, in areas with calcareous bedrock. An assignment of numerous collections from Yakutia to D. subandreaeoides was confirmed by ITS sequences; all these specimens possess both flagelliform innovations with small leaves (main diagnostic character of this species) and clusters of axillary gemmae (not characteristic for this species, only once tentatively mentioned previously) while gemmae were not observed in specimens from Chukotka, Altai and Sayan Mts, Buryatia, Irkutsk Province, and Zabaikalsky Territory. Mature sporophytes of Didymodon perobtusus are newly described; they were collected in 2022 in Tunkinsky Nature Park (Republic of Buryatia). Morphological distinctions between D. perobtusus and D. subandreaeoides are discussed, focusing on the differences in the perichaetial leaves and peristome. Didymodon nigrescens is found in collections from Sakhalin; this is the first record of the species from Russia. Descriptions, illustrations, and habitat data are provided for the three species, and distribution maps in Russia are also presented.