taxonID	type	description	language	source
03B5879F2F15FFEC7522FB21FAB37EA2.taxon	materials_examined	TYPE: Russia, Republic Sakha / Yakutia, Tomponsky District, Verkhoyansky Mountain system, Suntar-Khayata Range, ca. 63 ° 07 ’ N, 139 ° 00 ’ E, 980 m a. s. l., Sukhaya Creek, right bank, larch forest with Chosenia on low terrace, cliffs at slope base, on inclined rock surface, 23. VII. 2015, Ignatov & Ignatova 15 - 11 (Holotype MHA 9108739!, isotype MW 9035965!).	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F15FFEC7522FB21FAB37EA2.taxon	diagnosis	Diagnosis: the new species is similar to Didymodon daqingi J. Kou, R. H. Zander & C. Feng in having leaves with long, narrow acumina and long excurrent costae, occasionally fragile, and costae lacking ventral stereids, but differs from it in smaller leaves, partially bistratose lamina not only at margins, and smooth laminal cells.	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F15FFEC7522FB21FAB37EA2.taxon	etymology	Etymology: the species name corresponds to Siberia, a region of northern Asia where it is distributed.	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F15FFEC7522FB21FAB37EA2.taxon	description	Description. Plants small or medium-sized, in dense tufts, dark green or brownish-green, not glossy. Stems 1.0 – 1.5 cm long, simple or irregularly branched, with moderately large central strand. Leaves loosely appressed and slightly flexuose when dry, widely spreading when wet, 0.8 – 1.8 × 0.3 – 0.4 mm, moderately fragile or, rarer, not fragile, from ovate bases gradually or + abruptly tapered into long, linear-lanceolate acumina, canaliculate distally, not decurrent at bases; margins slightly recurved on both sides at proximal 1 / 2 – 3 / 4 of leaf, entire; costa moderately strong, 50 – 75 µm wide at leaf base, gradually narrowing upwards, long excurrent, strongly prominent dorsally, flat ventrally, with quadrate, smooth cells on both surfaces, without a pad of large, translucent cells on ventral surface below leaf apex, in transverse section semicircular, guide cells in 1 – 2 (– 3) layers, dorsal stereids in 1 – 3 layers, ventral stereids lacking or few substereids present in proximal part, ventral and dorsal epidermis differentiated; lamina partially bistratose distally at margins or near costa, or between costa and margins, unistratose in proximal part of leaf; cells in distal part of leaf rounded-quadrate and oblate, with angular lumina, 5 – 10 × 4 – 8 µm, smooth; basal leaf cells weakly differentiated, in few rows short rectangular, 15 – 25 × 6 – 10 µm, basal marginal cells quadrate and oblate. KOH reaction yellowish-green. Brood bodies absent. Dioicous, sporophytes unknown.	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F15FFEC7522FB21FAB37EA2.taxon	distribution	Distribution and ecology. Didymodon sibiricus is currently known from two close localities on Suntar-Khayata Mountain Range in Yakutia, on Byrranga Range in northern Taimyr (this is the northernmost known locality, at 74.47 ° N), and in several distant localities in southern Siberia: Republics Altai, Tyva, and Buryatia, and Zabaikalsky Territory. It was collected on outcrops on dry, open or forested slopes, in cliff niches, on siltstone and dolerite outcrops, at elevations 400 – 2100 m a. s. l. Differentiation. Didymodon sibiricus has a considerable similarity to the described from China D. daqingi, and its specimens were previously referred to this species (Ignatova et al., 2024). They are similar in leaf shape, with short, ovate bases and long, linear lanceolate acumina, long excurrent costa, and partially bistratose lamina. However, they differ in plant size and size of leaves: in D. sibiricus, leaves are shorter and narrower [0.8 – 1.8 (– 2.0) × 0.3 – 0.4 mm vs 2.0 – 2.8 × 0.4 – 0.5 mm], costa is more slender (50 – 75 vs 75 – 105 µm wide at leaf base), leaf margins are only slightly recurved in midleaf (much stronger recurved to revolute in proximal 1 / 2 – 3 / 4 of leaf in D. daqingi; lamina cells are smooth in D. sibiricus (vs weakly papillose in D. daqingi), and it possesses bistratose patches in distal part of leaf not only at margins but also near costa, or only in midleaf (leaf lamina is described as bistratose only at margins in D. daqingi). Another species described from Inner Mongolia, China, D. manhanensis C. Feng & J. Kou, has also a certain similarity with D. daqingi and D. sibiricus in leaf shape,	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F13FFEA7522F8FBFBBF7DFC.taxon	materials_examined	TYPE: Russia, southern part of Primorsky Territory, Ussurijsky State Reserve, 43.638943 ° N, 132.556431 ° E, ca. 177 m a. s. l., vicinity of Peyshula Field station, Zmeinaya Mt. northern slope. On cliff. 19. VIII. 2022, Fedosov 21 - 02 - 11 (Holotype MW 9131243!, isotype MHA 9132130!).	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F13FFEA7522F8FBFBBF7DFC.taxon	diagnosis	Diagnosis: the new species is similar to Didymodon glaucus Ryan in plant habit and leaf shape but differs from it in having leaves with 2 – 3 (– 4) - layered lamina in 1 – 4 marginal rows, basal laminal cells weakly differentiated, and in absence of brood bodies.	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F13FFEA7522F8FBFBBF7DFC.taxon	etymology	Etymology: the species name refers to the collecting locality of the type specimen, Ussurijsky Reserve and the name of the river Ussuri, which means ‘ black as soot ” in Manchu.	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F13FFEA7522F8FBFBBF7DFC.taxon	description	Description. Plants small to medium-sized, in loose or dense tufts, green or dark-green above, occasionally slightly glaucous, light brownish below, not glossy. Stems 0.7 – 1.5 cm long, repeatedly branched, with large central strand. Leaves loosely appressed, slightly flexuose when dry in proximal parts of shoots, upper leaves somewhat crisped, widely spreading when wet, 1.7 – 2.3 × 0.18 – 0.32 mm, linear lanceolate to linear, widely keeled distally, with narrow, 2 – 3 cells wide, 3 – 4 - layered, round in transverse section apical portions 0.1 – 0.3 mm long, not decurrent at bases; margins plane or weakly recurved in mid-leaf, entire; costa strong, 65 – 80 µm wide at leaf base, weakly tapering upwards, percurrent, strongly prominent dorsally, flat ventrally, with quadrate cells on both surfaces, papillose on ventral side, without a pad of large, translucent cells below leaf apex, smooth or weakly papillose on dorsal side, semicircular in transverse section, guide cells in 2 layers, 2 – 5 cells in each layer, dorsal stereid band 1 - 2 - layered, ventral stereid band absent, ventral and dorsal epidermis differentiated; lamina unistratose near costa and in midleaf, with 1 – 4 rows of 2 – 3 (– 4) - stratose cells at margins; cells in distal part of leaves round, short elliptic and oblate, 6 – 10 × µm, with moderately thickened, straight walls, with 1 – 4 low, bifurcate papillae on both surfaces; basal laminal cells weakly differentiated, chlorophyllose, rectangular, 20 – 40 × 9 – 11 µm, smooth, with moderately thickened walls. KOH reaction yellowish-green or yellow. Brood bodies absent. Dioicous, sporophytes unknown.	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
03B5879F2F13FFEA7522F8FBFBBF7DFC.taxon	distribution	Distribution and ecology. In addition to the type locality in Ussurijsky Reserve, Didymodon ussuriensis was repeatedly collected in Primorsky Territory on Lozovy Range and found once on Russkij Island. It was also revealed in collections from Amur Province (Tukuringra Range in Zeisky Reserve) and from Zabaikalsky Territory (Daursky Reserve). It grows on dry calcareous rocks and outcrops in oak and birch forests; it was also collect- ed on marble blocks on the bank of Zeya reservoir. Differentiation. Didymodon ussuriensis is habitually similar to D. glaucus in having linear-lanceolate leaves crisped at shoot tips in dry condition, occasionally also with glaucous tint. These two species share a specific structure of leaf tips, 2 – 3 cells wide, 3 – 4 - layered, round in transverse section. However, D. ussuriensis possesses strongly thickened leaf margins, 2 – 3 (– 4) - layered in 1 – 4 rows of cells, flat or weakly recurved at short distance at mid-leaf, whereas in D. glaucus leaf margins are always unistratose and recurved. Also D. ussuriensis lacks brood bodies (in D. glaucus they are frequently numerous), and its basal laminal cells are poorly differentiated, chlorophyllose. The latter character distinguishes it also from D. australaisiae, which shares with it having 2 – 3 - stratose leaf margins; D. australaisiae has shorter, lanceolate leaves, costa with a pad of large, translucent cells on ventral surface below leaf apex, and rhizoidal tubers. The latter species is resolved in the molecular-phylogenetic tree (Fig. 1) in the clade representing the genus Trichostomopsis sensu Jiménez et al. (2022), whereas Didymodon ussuriensis is found in the terminal clade of Didymodon s. str. There is some resemblance between D. ussuriensis and D. sibiricus in leaf shape, as they have long and narrow, liner-lanceolate leaves with partially bistratose lamina, costa with guide cells in 2 – 3 layers, lacking ventral stereids; however, D. sibiricus possesses wider leaf bases, 0.3 – 0.4 mm wide (vs 0.20 – 0.35 mm wide), leaf laminae with bistratose patches not only at margins, and smooth laminal cells (densely papillose in D. ussuriensis). Additional specimens examined: RUSSIA: Zabaikalsky Territory: Borzya District, Daursky Reserve, 16. VII. 2010 E. S. Prelovskaya (LE B- 0047621). Amur Province: Zeysky Reserve, Zeya Reservoir coast between Razvedochny and Sukhoy Gulfs, outcrops, S. V. Dudov & M. N. Kozhin 2016 _ Br _ 1006 (MW 9111441). Primorsky Territory: Partizansk District, Lozovy Range, Ignatov, Ignatova & Cherdantseva 06 - 2814 (MHA 9109004); Russkij Island, vicinity of Melkovodnaya Bay, Fedosov 24 - 351 - 18 (MW 9133389).	en	Ignatova, E. A., Fedosov, V. E., Fedorova, A. V., Kuznetsova, O. I., Ignatov, M. S. (2025): Two new species of Didymodon (Pottiaceae, Bryophyta) from Asian Russia. Arctoa 34 (1): 24-30, DOI: 10.15298/arctoa.34.02, URL: https://doi.org/10.15298/arctoa.34.02
