Grimmiaceae. Genus Schistidium

1. Dioicous, sporophytes very rare; plants very small, shoots filiform, julaceous; hair-points present, coarsely spinulose; upper lamina partly bistratose 50.S. tenerum

An arcto-alpine species, known in Asian Russia in the Arctic and Subarctic from Taimyr to Chukotka, in the permafrost zone of Yakutia and Magadan Province and also in Kamchatka (southernmost locality at ca. 55° N). Grows on cliffs and rocks on open slopes and in larch forests, up to 1000 m a. s. l. The combination of characters presented in the key distinguishes this species from all other Schistidium species.

Autoicous; plants small or large; shoots not thread-like, leaves not strongly imbricate; hair-points present or absent, entire or toothed; upper leaf cells unistratose, partly or completely bistratose 2
2. Leaves awned; costae excurrent as a yellowish, chlorophyllose awn 3
Leaves muticous or with hyaline hair-points; costae ending well below apex, percurrent or extending into the lower portions of hair-points 5
3. Leaf margins plane; awns in upper and perichaetial leaves long, smooth; costae 4-6-stratose, sometimes bulging on ventral side, in transverse section with substereids and more or less clearly differentiated dorsal and ventral epidermal cells 21. S. frahmianum

Recently described subarctic species known from several localities in Chukotka and western Alaska, also found in one locality in Yakutia (northern part of Verkhoyansky Mt. Range). Grows on rocks in brooks (up to 1200 m a. s. l. ). It is similar to S. agassizii, but differs in having stronger costae that are rounded in transverse section and excurrent into a short or rather long, stout mucro.

Leaf margins recurved; awns in all leaves short and toothed; costae 2-3(-4)-stratose, flat on ventral side, in transverse section with cells undifferentiated 4
4. Awns finely denticulate, often recurved when dry; upper leaf cells isodiametric and transversely oval; median leaf cells slightly sinuose 43. S. sibiricum

A recently described species that is rather common in the south of Russian Far East (present in Sakhalin, but absent in Kuril Islands), sporadic in Kamchatka and southern Siberia, found in a few localities in the Urals (South and North); also known in Murmansk Province from recent collections as well as one old, re-identified specimen. Its presence in SW Finland was confirmed by molecular data. Grows on rocks in brooks and small rivers and along their banks, on lake shores (rather common along Baikal Lake), rarer on mountain slopes in river valleys away from water courses mostly in forest zones or slightly above timberline, up to 1000 m in Transbaikalia. In plant size and habit S. sibiricum is similar to S. apocarpum, but differs in having clorophyllose awns instead of hyaline hair-points.

Awns sharply denticulate, straight when dry; upper leaf cells short rectangular; median leaf cells ± strongly sinuose 10.S. canadense

This species is rather common in eastern North America and has been found once in European Russia (Karelia). The identity of the Russian record was confirmed by molecular data. Grows on acidic rocks in shady places. It is very similar to S. sibiricum, but differs in the characters presented in the key.

5(2). Costae 4-6-stratose, often bulging on ventral side, usually with guide cells and often 2 stereid bands in transverse section; in spray zone on sea shores 31. S. maritimum

This species is restricted to the sea coastal zone of Eurasia and North America. It is rather common along sea shores of Barentz and White Seas in north European Russia and along coasts of Kuril and Kommander Islands in the Russian Far East. Found once in Sakhalin, but absent in Primorsky Territory and Kamchatka. Grows on sea shore cliffs and small rocks, occasionally also on artificial substrates (concrete). Features helpful for species recognition, even when sterile, include costae with stereid bands; stiff, narrowly lanceolate leaves; leaf apices muticous or with short hyaline tips; laminae partially bistratose; and often mammillose leaf cells.

Costae 2-3(-4)-stratose, rarely 5-stratose (in S. holmenianum), flat on ventral side, with undifferentiated cells in transverse section; in various habitats 6
6. Upper leaf cells 11-14 m wide 24. S. grandirete

A rare circumarctic species common in Russia on the Arctic Ocean islands, and known from scattered localities in Taimyr Peninsula, Putotana and Anabar Plateau. Grows in rock fields and on wet rocky slopes in rocky tundras and polar deserts. This species can be recognized by its large plants; large upper leaf cells; weakly papillose costae; occasionally lightly papillose leaf cells; and large spores, 15-21 m.

Upper leaf cells 6-11(-13) m wide 7
7. Upper and median leaf cells papillose 8
Upper and median leaf cells smooth (but leaf margins and dorsal side of costae may be papillose) 13
8. Hair-points papillose dorsally in lower part, coarsely spinulose-denticulate throughout; leaf cell papillae broad 23. S. frisvollianum

Circumpolar arctic/subarctic species. In Russia comparatively frequent in Taimyr Peninsula and Anabar Plateau (southward to ca. 70°N), arctic Yakutia and Chukotka and on islands in Arctic Ocean, also found in the middle course of Lena River in Yakutia (ca. 61°N) and in NE European Russia. Grows on limestone and dolomite rocks, on rock surfaces, ledges covered with fine soil and in crevices, on rock fields. It can be recognized by its rather small, brown colored plants that have broad, rounded papillae on the dorsal surfaces of flattened hair-points and leaf cells.

Hair-points not papillose dorsally, finely and distantly spinulose-denticulate throughout; leaf cell papillae narrow 9
9. Upper leaf laminae with bistratose patches or striae or predominantly bistratose; stem central strands distinct 10
Upper leaf lamina unistratose; stem central strands absent or indistinct 12
10. Peristome teeth strongly reduced, 25-30 m long 49. S. succulentum

This species was recently discovered in alpine habitats in the Caucasus (Karachaevo-Cherkessian Republic) and subsequently found in a few localities in Asian Russia, i. e. , Southern Taimyr and Zabaikalsky Territory. In the Caucasus it grows at 2600-3000 m a. s. l. on granite and schist rock outcrops in alpine meadows. S. succulentum is similar to S. flaccidum in having small plants and strongly reduced peristome teeth, but differs in having partially bistratose and occasionally papillose leaf lamina, perichaetial leaves with narrow, stiff hair-points, cylindrical urns and long-beaked opercula.

Peristome teeth perfect, >250 m long 11
11. Upper and central leaf cells 6-9 m wide, round and oval, esinuose or slightly sinuose 35. S. pruinosum

A mostly European species known in Russia from the Caucasus and found in a few localities in the Urals and Asian Russia (Zabaikalsky and Khabarovsk Territory). Grows mostly in forest zone on calcareous rocks as well as schists and granites. It can be recognized by its partially bistratose and usually densely papillose leaf lamina and small upper leaf cells.

Upper and central leaf cells 8-11 m wide, oblong at least in central part, sinuose 12. S. confusum

A rare European species collected in Russia only once in Karelia (NW European Russia). Grows on sunny calcareous rocks. It is similar to S. pruinosum in having partially bistratose leaf laminae, but the bistratose patches are less numerous, the leaf cell papillae fewer and the upper leaf cells wider.

12(9). Leaf cells with strongly sinuose, dark reddish walls; plants mostly dull black, leaf lamina uniformly colored; peristome teeth 220-330 m long 8. S. boreale

In European Russia this species is known in Kola Peninsula and Karelia, Komi Republic, North and South Urals and in limestone areas in the lowlands (Lipetzk Province). In Asian Russia it is rather frequent in southern Taimyr, sporadic in Yakutia, and found in several localities in southern Siberia, Subpolar Urals and Chukotka. Grows mostly at low altitudes, rarely higher, to 1800 m a. s. l. , in various types of tundra, sometimes in larch and stone birch forests, on calcareous rocks (limestone, dolomite, iolite, dolerite), rarely on acidic rocks, and on soil. Its diagnostic characters include dark plants with leaves that have papillose cells and costae, dark reddish cell walls and straight hair-points.

Leaf cells with moderately sinuose, green or brown walls; plants olivaceous or reddish, leaf lamina often with reddish patches; peristome teeth 220-500 m long 33. S. papillosum

Widespread circumboreal species. In European Russia it is frequent in Kola Peninsula and Karelia, in Urals and in the Caucasus, but absent in lowlands, except a few places in Leningrad Province. It is known throughout Asian Russia, frequent in Taimyr, mountain areas of Yakutia, southern Siberia and Russian Far East from Primorsky Territory to Chukotka and in Kuriles, Sakhalin and Kommander Islands; it has also been reported in the high Arctic (islands in Arctic Ocean). Grows in forest and alpine zones in mountains and in tundras, on various types of rocks (acidic and basic) and on soil in shady and sunny places both dry and rather wet. The species can be recognized by its leaves that have papillose laminae and costae, usually flexuose hair-points, and frequent presence of red spots or strips on the lamina.

13(7). Plants robust, dark reddish or black, in extensive tufts or mats on soil in arctic tundra and fens 14
Plants medium-sized or small, rarely robust, various in color, in small tufts, mostly on rocks 15
14. Costae strongly projecting dorsally, 3-5-stratose at mid-leaf; upper leaf cells subquadrate, 7-10 m wide; cell walls straight, brownish 26. S. holmenianum

Arctic species with a scattered distribution in Russia from Taimyr to Chukotka and on Arctic Ocean Islands. Grows on soil in wet tundras and forms large black cushions that occasionally have a reddish tint. Growing on soil in the tundra separates it from most species of the genus. It is most similar to S. andreaeopsis, but differs in having stronger costae and smaller leaf cells.

Costae weakly projecting dorsally, 2(-3)-stratose at mid-leaf; upper leaf cells rectangular, 10-12 m wide; cell walls sinuose, dark reddish 3. S. andreaeopsis

This species is distributed in the Arctic and Subarctic of Asian Russia from Taimyr to Chukotka, in islands of the Arctic Ocean, and known from a few localities southward in the permafrost zone of Yakutia. Grows on soil and fine soil in tundras and arctic deserts mostly in calcareous areas, sometimes as a dominant species. This species is rather similar to S. boreale in overall appearance and both species have dark colored plants and cell walls, as well as similar lamina areolation, but unlike S. boreale it always lacks papillae on its leaf cells and costae.

15. Peristome teeth absent or less than 150 m 16
Peristome teeth more than 200 m 19
16. Stem leaf apices obtuse or rounded, occasionally with stiff, very short, narrow hyaline apicula; lamina partly bistratose 17
Stem leaf apices acute, with weak, flattened hyaline hair-points; lamina unistratose 18
17. Plants jet-black; leaf margins plane above; urns short-cylindrical; exothecial cells predominantly oblong in central and lower part of urns 5. S. atrofuscum

Mostly European montane species, very rare in North America; found in Russia only once in the Caucasus, Karachaevo-Cherkessian Republic. Grows on open calcareous cliffs. The combination of small plant size, jet-black color, obtuse leaf apices and leaf cells with thick, straight walls is helpful for its recognition.

Plants dark-green; leaf margins recurved to shortly below leaf apices; urns cylindrical; exothecial cells predominantly isodiametric and transversely rectangular in lower part of urns 49. S. succulentum
18. Leaf margins unistratose; leaf cells with strongly thickened walls; perichaetial leaves not plicate; opercula long-beaked 15. S. cryptocarpum

In Russia this species is known from a few localities in Chukotka, Kamchatka and Kommander Islands. Grows on rocks and soil in tundra, on moraine ridges near glaciers and on wet rocks in brook canyons. It can be separated from most other species of the genus by its cupulate capsules with strongly reduced peristome teeth, and from S. flaccidum by its longer hair-points and beaked (not mammillate) opercula.

Leaf margins bistratose; leaf cells with moderately thickened walls; perichaetial leaves plicate; opercula very short-beaked 19. S. flaccidum

A mostly European species also known from western North America. In European Russia its presence was confirmed for the Caucasus, in Karachaevo-Cherkessian Republic to Dagestan, Rostov Province, Karelia and Murmansk Province; in Asian Russia it was collected once in Altai Republic. All other Russian records of S. flaccidum belong to another species. Grows mostly in alpine zones in the mountains, at 2000-3800 m a. s. l. , rarer at lower altitudes, both on calcareous and acidic rocks. It can be recognized by the unique combination of cupulate capsules, strongly reduced peristome teeth, weak and flattened leaf hair-points and mammillate opercula.

19(15). Capsules short cylindrical or cupulate, length/width ratio 0.8-1.3 20
Capsules oblong cylindrical, length/width ratio > 1.3 31
20. Exothecial cells incrassate, irregular in shape; leaf hair-points absent 21
Exothecial cells thin-walled, subquadrate or rectangular; leaf hair-points usually present, rarely absent 23
21. Leaves linear-lanceolate or lingulate, weakly keeled above 2. S. agassizii

This species is very common in Murmansk Province and Karelia, scattered in Vologda and Arkhangelsk Provinces and in the Urals, found once in the Caucasus and sporadically distributed in Asian Russia, mostly in permafrost zone (Taimyr, Yakutia and Chukotka). Also known from a few localities in Kamchatka, Russian Far East and southern Siberia. Grows on rocks, boulders and pebble bars along stream courses and lakes or submerged in water, mostly on acidic rocks. It is recognized by its rather long leaves with obtuse apices and flat margins, unistratose lamina and short, cupulate capsules with thick-walled, irregular exothecial cells.

Leaves ovate-lanceolate or ovate, sharply keeled above 22
22. Plants robust; leaf apices acute; leaf margins distantly denticulate above, bistratose, recurved in lower 1/2-3/4 or to near apices; laminae often with bistratose patches 39. S. rivulare

This species is widely distributed in cold areas and in tropical mountain regions throughout the world. It is sporadic in the mountain regions of Russia but there are few records of it in the lowlands in places with rocky substrates. Grows on acidic and calcareous rocks along stream courses and on submerged or temporarily flooded boulders. Its diagnostic characters include sharply keeled leaves with denticulate upper margins that always lack hair-points, cupulate urns with thick-walled, irregular exothecial cells, and subentire or only slightly perforate peristome teeth.

Plants slender; leaf apices rounded; leaf margins smooth, unistratose, recurved to near apices; laminae unistratose 45. S. sordidum

A mainly arctic/subarctic Eurasian species. In European Russia it is known only in Komi Republic; in Asian Russia its distribution is mostly restricted to the permafrost zone (Taimyr, Yakutia, Chukotka, Magadan Province). It was also found in Kamchatka and Subpolar Urals and was reported from Zabaikalsky and Khabarovsk Territories. Grows on rocks and fine soil along brooks and streams, near late snow-beds, and on ledges of wet cliffs, preferably on acidic rocks. The species is distinguished by the combination of small-sized plants; elliptic leaves rounded at apices with narrowly recurved margins almost throughout; and short, cupulate urns with irregular, thick-walled exothecial cells.

23(20). Hair-points thin, wide, distinctly flattened throughout 24
Hair-points thick, narrow or widened at base, rounded 26
24. Leaf hair-points sharply dentate with strong, often recurved teeth 11. S. confertum

In Russia this species is known only from North Ossetia in the Caucasus. All other Russian records of the species are based on erroneous identifications. Grows on dry rocks in sunny places. It can be recognized by its small plants and leaves that have flattened hair-points with sharply dentate margins.

Leaf hair-points finely denticulate or denticulate-spinulose with small, blunt teeth 25
25. Leaf hair-points very long, to 1.2 mm in perichaetial leaves, transiting into hyaline upper portion of leaf lamina; costae strongly projecting dorsally, trapezoid in transverse sections, extending into the hair-points 7. S. bakalinii

This species is known from only two Kuril Island records (Shikotan and Iturup Islands) in the Russian Far East. It was collected in tufa cliff crevices on a forested, N-faced slope and on rock outcrops at the sea shore. It can be recognized by its lanceolate leaves with very long, wide, distinctly flattened hair-points; costae that extend into the lower part of the hair-points; and rather strongly sinuose leaf cells. It is similar to S. scabripilum and S. austrosibiricum, but differs in having practically smooth (vs. scabrose) hair-points.

Leaf hair-points moderately long, to 0.5 mm in perichaetial leaves, upper portion of lamina chlorophyllose; costae weakly projecting dorsally, semicircular in transverse sections, ending at or below the hair-points 51. S. tenuinerve

This species was recently described from Sakhalin Island in the Russian Far East. It is sporadically distributed in Asian Russia (Kamchatka, Kommander and Kuril Islands, southern Taimyr, Yakutia and southern Siberia) with one disjunct locality in Murmansk Province on the shore of the White Sea. Grows from sea level to alpine zone, on treeless, rocky plateaus in Taimyr, on rock outcrops on mountain slopes, in wet rocky tundra, and along water courses on schists, quartzites, basalts, volcanic rocks. Its diagnostic characters include small plants and leaves with thin, narrow costae, and weak, flattened hair-points that have finely serrulate margins and smooth surfaces.

26(23). Spores 13-25 m 27
Spores 8-13 m 28
27. Leaves broadly triangular, 1.4-2.3 x 0.5-1.0 mm; margins bistratose througout; plants dark-green, blackish or yellow-olivaceous, rarely reddish 34. S. platyphyllum

This species is common throughout the arctic/subarctic zones, including Arctic Ocean islands, in permafrost areas of Asian Russia; it is rare in Urals and sporadic in southern Siberia and southern Far East (Kamchatka, Sakhalin and Kommander Islands, but not the Kuril Islands). Grows on rocks of various types (occasionally on artificial substrates) from sea level to the lower alpine zone (ca. 2000 m a. s. l. ) on rocks or boulders along or in water courses, on pebble bars, on wet, rocky soil below melting snow fields, in tundras and polar deserts, on wet cliff ledges and vertical surfaces. It is separated from S. rivulare by having thin-walled, oblong exothecial cells (vs. thick-walled, irregular, more or less isodiametric); frequent presence of leaves with short, hyaline hair-points (vs. absent); and strongly perforate peristome teeth (vs. subentire).

Leaves narrowly triangular (Didymodon-like), 1.4-2.0 x 0.5-0.8 mm; margins often with unistratose patches; plants often reddish or ferrugineous 1. S. abrupticostatum

A circumarctic species known in Russia from the Arctic Ocean islands, lower courses of Lena and Kolyma Rivers, and rather common in Taimyr. Grows on rocks along and in streams, on pebble bars, in rock fields, and near snowbeds; once collected on whale bones on the sea shore. The species is similar to S. platyphyllum in sporophyte structure and leaf areolation, but differs from it in the characters presented in the key.

28. Leaf hair-points long, dentate with distant, sharp, often recurved teeth; costae semicircular in transverse sections 29. S. liliputanum

This species is rather common in East Asia, including Russian Far East and Transbaikalia; it is also known from sporadic reports in Altai and Kemerovo Province, southern Taimyr, Yakutia, Magadan Province and Kamchatka. Grows in lowlands and lower mountain zone on dry rocks (gneiss, basalt, schist, diorite) in open and shady places, occasionally on rocks along streams and along the sea shore. Its main diagnostic characters include small, often reddish plants; long, narrow leaf hair-points with distant, often recurved teeth; and subquadrate basal marginal leaf cells.

Leaf hair-points short, finely denticulate, occasionally absent; costae often trapezoid or irregularly angular in outline in transverse sections 29
29. Plants medium-sized to large, black or dark brown; alar regions with 5-7 rows of enlarged (wider than upper cells) basal marginal cells 38. S. relictum

This species is known in Alaska, Northwest Territories, Nunavut, Yukon and British Columbia in northern North America as well as several localities in Asian Russia: southern Yamal, Taimyr, northern and eastern Yakutia. Grows at low elevations on calcareous rocks in wet, open habitats. The species is distinctive in having dark, brownish to black plants; evenly foliated, column-like stems; leaves occasionally in spiral rows; very short or absent hyaline hair-points; and rather conspicuous alar regions with multiple rows of enlarged, subquadrate cells.

Plants small to medium-sized, olivaceous or brownish, sometimes with rusty tint; alar regions not differentiated 30
30.Plants small; stem central strands distinct; upper leaf margins smooth; costae trapezoid in transverse sections, smooth dorsally 53. S. umbrosum

This species is very rare in Russia, known from a few scattered localities in Murmansk Province, Taimyr, Yakutia and Chukotka. Grows at low elevations on dry and wet rocks (granite, sandstone and limestone) in open places. It is similar to S. pulchrum, but differs in having smaller plants; shorter, stiff leaf hair-points; shorter urns; and strongly perforated peristome teeth.

Plants medium-sized; stem central strands indistinct; upper leaf margins denticulate; costae irregularly angular in transverse sections, usually papillose dorsally 27. S. konoi

This species has a restricted distribution in Japan and Russian Far East (Southern Kuril Islands, Primorsky Territory and Kamchatka). Grows at low elevations in shady and open places on cliff ledges and vertical rock surfaces. It is very similar to the widespread Russian Far Eastern S. lancifolium but differs in having brownish plants (vs. olivaceous); shorter urns; weaker denticulate upper leaf margins; and costae that are irregularly angular in transverse section (vs. semicircular).

31(19). Upper leaf margins denticulate or papillose-crenulate above 32
Upper leaf margins smooth throughout 39
32. Exothecial cells predominantly oblong in central and lower part of urns 33
Exothecial cells predominantly isodiametric and transversely rectangular in central and lower part of urns 36
33. Leaf lamina partially bistratose above 13. S. crassipilum

In Russia this species is frequent throughout the Caucasus (at lower elevations, up to 2200 m alt. ) and known from a few records in lowland central European Russia, Karelia, southern Murmansk Province, southern Urals and Altai. Grows in open and shady places, mostly on calcareous rocks (limestone, shell gravel, sandstone), often on artificial substrates (concrete, asphalt) and occasionally on rocky soil. It can be confused with S. apocarpum, but differs in having leaves with plane upper margins and more regularly bistratose leaf cells; oblong (vs. subquadrate and transversely rectangular) exothecial cells; and peristome teeth straight and squarrose, rather than twisted and incurved when dry.

Leaf lamina unistratose 34
34. Leaf hair-points present in most leaves, 0.3-0.6 mm long, distinctly flattened in lower portion; uppermost leaf margins finely papillose-crenulate 6. S. austrosibiricum

This species occurs in southern parts of Asian Russia from Amurskaya Province to Altai Mountains with northernmost localities in southern Yakutia. It was collected in mountain areas at low altitudes (ca. 300-950 m a. s. l. ) within the forest zone in mainly dry, open places such as limestone outcrops on mountain slopes, rocks in meadows and on steppe slopes. It can be recognized by its leaves that have distinctly flattened, finely scabrose, hyaline hair-points; sharply serrate margins; papillae on the dorsal side of the costae and distal leaf margins; and mostly unistratose leaf cells. In addition, it has rectangular exothecial cells. It is most similar to S. sinensiapocarpum, but that species differs from it in having narrow, rounded, sharply serrate hair-points; lamina with larger bistratose areas; and subquadrate or transversely rectangular exothecial cells.

Leaf hair-points present only in upper and perichaetial leaves, to 0.15 mm long, terete; uppermost leaf margins sharply or obtusely denticulate 35
35. Leaf margins recurved to near apices, coarsely papillose-denticulate above; alar cells not differentiated 14. S. crenatum

A mostly northern circumpolar species. It is sporadic in Russia: Murmansk Province, Northern and Subpolar Urals (both slopes), Yamal, Taimyr, Yakutia, Chukotka, Transbaikalia, Altai and Novosibirsk Province. Grows at low elevations in the north and in the alpine zone in the southern mountains (to 2400 m a. s. l. ), on calcareous and acidic rocks, along stream courses and on wet cliff ledges, rarer in dryer habitats. It differs from other species of the genus in having widely acute upper stem and perichaetial leaves with very short, hyaline apicula and distinctly papillose-denticulate or crenate uppermost margins. Its perichaetial leaves are considerably larger than the stem leaves and also differ in having oblong bases.

Upper leaf margins flat, obtusely denticulate; alar regions with 5-7 rows of enlarged (wider than upper cells) basal marginal cells 38. S. relictum
36(32). Peristome teeth narrowly acuminate, erect, apices incurved forming a dome; columellae persistent after dehiscence 37
Peristome teeth acute, erectopatent, apices not forming a dome; columellae falling with opercula after dehiscence 38
37. Plants jet-black; urn length/width ratio 1.3-2.1; shoots straight 52. S. trichodon var. trichodon

This species is very rare in Russia. It was found in two localities on Sakhalin Island: on rock outcrops on a north-facing slope and on rocks in mountain tundra, at 600-900 m a. s. l. The most distinctive characters of the species are its dome-shaped peristome and exceptionally long, narrow peristome teeth. The type variety is characterized by having jet-black plants; straight shoots; and short-cylindrical capsules.

Plants olivaceous or brownish; urn length/width ratio 1.6-2.4; shoots arcuate, secund 52a. S. trichodon var. nutans

This variety is more frequent in Russia than var. trichodon. It is somewhat common in Central/Eastern Caucasus and sporadically distributed in North Urals, Altai/Western Sayan Mts. , Sakhalin and Kamchatka. Grows in forest and low alpine zones in the mountains on granite and calcareous rocks in rather dry, shaded or sunny habitats. Differs from the type variety by the characters given in the key.

38. Plants medium-sized; upper leaf margins strongly and irregularly serrate; costae with high papillae on dorsal side 28. S. lancifolium

A boreal and temperate species that grows in lowlands and the forest zone of mountains. In European Russia it is known from Karelia, southern part of Murmansk Province, some central provinces, Urals and is very common in the Caucasus. In Asian Russia it is also very common in southern areas of the Far East but rarer in Kamchatka and Kommander Islands, sporadically distributed in southern Siberia, and known from a few records in Transbaikalia. Grows at low altitudes (up to 1600 m in Sikhote-Alin Mts. , Primorsky Territory) under forest canopies and in open places in moderate moisture conditions on acidic and calcareous rocks (including limestone), occasionally on artificial substrates. It differs from S. apocarpum in having smaller plants and narrower leaves with stronger serrate, upper margins and higher papillae on the costae.

Plants medium sized to large; upper leaf margins finely denticulate; costae with scattered, low papillae on dorsal side 4. S. apocarpum

A mostly European species common in NW European Russia where granite boulders are widespread, sporadic in central lowland provinces and in Urals, moderately frequent in the Caucasus. Eastward of Urals it is known from a few records in Altai and Kuznetzky Alatau Mts. Grows in lowlands and in forest zones in the mountains, in open or shady, moderately moist habitats, preferably on granite rocks, but occasionally on calcareous rocks and artificial substrates. For differences from S. lancifolium and S. crassipilum see comments under those species.

39(31). Basal leaf cells thin-walled, oblong, aporose, sharply demarcated from thick-walled, strongly sinuose median leaf cells; basal marginal cells forming a hyaline border 40
Basal leaf cells moderately thick-walled, rectangular, porose or aporose, gradually transiting to median leaf cells; basal marginal cells not differentiated 41
40. Plants olivaceous above, medium-sized; stems to 10(-30) mm long; leaves to 2.1 mm long; leaf cell walls light-colored, strongly thick-walled; hair-points 0-0.8 mm long 22. S. frigidum

This northern species is very rare in European Russia (Murmansk Province and Karelia), but in Asian Russia it is very common in Taimyr and moderately frequent in Yakutia, Chukotka and Kamchatka. It is known also from Subpolar Urals, Yamal and islands in the Arctic Ocean. Grows in treeless areas and open larch forests at low elevations in open, moderately wet or rather dry places on acidic and calcreous rocks (basalt, porphirite, sandstone). The species is peculiar in leaf lamina areolation: its distal and median laminal cells have very strongly incrassate and strongly sinuose walls, while cells at leaf base are contrastingly thin-walled and non-porose, forming a well delimited transparent zone; there is also rather conspicuous marginal hyaline border. See also comments to S. obscurum.

Plants jet-black or dark brown above, rarely olivaceous, small; stems to 1.5 mm long, leaves to 1.3 mm long; leaf cell walls dark-colored, moderately to strongly thick-walled; hair-points 0-0.3 mm 32. S. obscurum

A montane Eurasian species very similar to S. frigidum but differing mainly in its smaller sized, darker colored plants. In Russia it is known from Karachaevo-Cherkessia in the Caucasus, Kemerovo Province, Transbaikalia, southern Taimyr, southern Yakutia, Kamchatka and Kommander Islands. Grows mainly at upper elevations in the alpine zone, rarely at lower altitudes on shady northern slopes, vertical walls, ledges and in crevices of cliffs and rock (often calcareous) outcrops.

41. Leaf hair-points distinctly flattened throughout or in basal portion, transitioning into hyaline upper portion of leaf lamina 42
Leaf hair-points terete, sometimes slightly widened at base, or hair-points absent 51
42. Exothecial cells predominantly oblong in central and lower part of the urns 43
Exothecial cells predominantly subquadrate and transversely rectangular in central and lower part of the urns 49
43. Leaf hair-points finely denticulate with distant, obtuse spinulae; upper leaf cells partially or totally bistratose; lower leaf cells arranged in oblique rows 54. S. venetum

Rare species found in Russia only in Murmansk Province and southern Taimyr. Grows on wet cliff ledges and mostly acidic rocks and boulders. Critical features of this species include small, ovate-lanceolate leaves; upper leaf laminae almost completely bistratose; rectangular basal leaf cells in oblique rows; leaf hair-points short, weak, flattened, almost entire; and peristome teeth strongly perforate.

Leaf hair-points clearly denticulate with distant, sharp teeth or dense, obtuse spinulae; upper leaf cells unistratose or with few bistratose strips; lower leaf cells arranged in straight rows 44
44. Leaf hair-points with dense, long, obtuse, finger-like spinulae, often recurved at right angles 17. S. echinatum

A rare mountain species known from a few records in the Urals, Caucasus, Alps (Austria) and western North America (California). Grows at low elevations and in forest and alpine zones in mountains (up to 2950 m in the Caucasus) mainly on calcareous rocks. It can be recognized by its small plants; partially bistratose leaf laminae; costae flattened and irregularly angular in transverse sections; and especially by its distinctly flattened, densely scabrose hair-points that are covered by long, obtuse, often recurved spinulae. See also comments under S. scabripilum.

Leaf hair-points with distant, sharp, sometimes recurved teeth or with dense, short, straight, obtuse spinulae 45
45. Leaf hair-points to 0.3(-0.4) mm long in upper and perichaetial leaves 46
Leaf hair-points to 0.7(-0.8) mm long in upper and perichaetial leaves 47
46. Plants small to medium-sized, green; leaves loosely appressed when dry, moderately widened at base, not shouldered; urns light brown; peristome teeth bright red 37. S. recurvum

A rare mountain species found twice in Russia (Byrranga and East Sayan Mts. ). Grows at low elevations in niches of wet rock outcrops (dolerite) and on rocky and loamy soil on mountain slopes. It can be recognized by its ovate-lanceolate leaves with long, widely recurved margins; comparatively short, weak and flattened hair-points with wide, recurved teeth; median laminal cells with strongly thickened sinuose walls; rectangular exothecial cells; and bright red, subentire peristome teeth.

Plants medium-sized to large, often brownish; leaves of fertile shoots closely appressed when dry, subsheathing at base, shouldered; urns dark brown; peristome teeth reddish-brown 47. S. subjulaceum

Rare boreal species known in Russia from the Baikal Lake area, Zabaikalsky Territory and East Sayan Mts. Grows in forest and alpine zones mainly on boulders along and in streams, lake shores, or periodically flooded places, rarely in dryer habitats. Its distinctive features include comparatively wide, ovate-lanceolate, shouldered leaves that clasp the stems; long, recurved leaf margins; short, narrow leaf hair-points; elongate exothecial cells; and subentire peristome teeth.

47. Leaf hair-points sharply dentate with strong, wide, often recurved teeth; upper leaf margins flat 11. S. confertum
Leaf hair-points serrate with sharp, narrow, straight teeth; leaf margins recurved nearly throughout 48
48. Leaf hair-points weak with sharp, narrow, distant spinulae on margins and dorsal surface; costa percurrent, smooth on dorsal side; median leaf cells thick-walled, weakly sinuose 42. S. scandicum

A rare species known from the mountains in Scandinavia, and southern Murmansk Province and Urals in Russia. Grows at low elevations in forested areas and moderately dry habitats in crevices of calcareous rock outcrops and boulders. Its diagnostic characters include long, narrow, but distinctly flattened hair-points with short, distant spinulae; unistratose leaf cells with strongly thickened, slightly sinuose walls; and rectangular exothecial cells.

Leaf hair-points strong with sharp, dense teeth at margins, finely scabrose on dorsal surface; costae often extending into lower portion of hair-points, papillose on dorsal side; median leaf cells moderately thick-walled, weakly sinuose 6. S. austrosibiricum
49(42). Leaf hair-points with short, dense, sharp, erect spinulae at margins and on dorsal surface; costae extending into the lower portion of hair-points; upper leaf lamina partially bistratose 41. S. scabripilum

A rare species with a scattered distribution in mountain areas in the permafrost zone of Asian Russia. It is known from Indigirka River basin (Yakutia), Anadyr River basin (Chukotka), Anabar and Putorana Plateaus (southern Taimyr). The species occurs at comparatively low altitudes (250-900 m a. s. l. ) within the open larch forest zones, and grows on siliceous rocks (sandstone, gneiss, dolerite, andesite, schist). It differs from S. echinatum mainly in having sharply scabrose hair-points with shorter, sharp spinulae that are erect rather than recurved at right angles.

Leaf hair-points finely denticulate at margins, smooth or with a few short spinulae on dorsal surface; costae percurrent; leaf lamina unistratose 50
50. Costae weakly projecting dorsally, 2-3-stratose; median leaf cells with moderately thickened and slightly sinuose walls 51. S. tenuinerve
Costae strongly projecting dorsally, 3-4-stratose; median leaf cells with strongly thickened and strongly sinuose walls 20.S. flexipile

This species was described from the Caucasus (North Ossetia), but since then has been collected only once in this region (Ingush Republic). Most recent collections of the species were made in Northern Europe and NE North America. In Russia it is also known from Murmansk Province, Karelia, Arctic Ocean islands, Yakutia and Chukotka. Grows at low elevations in open or shady, moderately wet places on calcareous rocks and in rocky tundra. The species can be recognized by its conspicuously enlarged perichaetial and subperichaetial leaves; narrow stem leaves; and laminal cells with strongly thickened, sinuose walls. Hyaline hair-points are rather long and flexuose in Caucasian plants, but comparatively short in northern collections of the species.

51(41). Exothecial cells predominantly isodiametric and transversely rectangular in central and lower part of urns 52
Exothecial cells predominantly oblong in central and lower part of urns 55
52. Upper leaf margins 2-4-stratose in 2-3 rows; costa flattened dorsally, trapezoid or irregularly angular in transverse section 30.S. marginale

A mountain species known from the Alps in Central Europe, Russian Caucasus (locally rather frequent), sporadically distributed in Transbaikalia and found once in Murmansk Province, Putorana Plateau, Altai and Kuznetzky Alatau Mts. Grows in forest and alpine zones (up to 2950 m in the Caucasus) on acidic and slightly base-rich rocks. Important features for its identification include small plants with narrow leaves that have conspicuously incrassate margins, partially bistratose laminae, weakly sinuose laminal cells and costae trapezoidal or irregularly angular in transverse sections.

Upper leaf margins 2-stratose in 1 row; costa not flattened dorsally, semicircular in transverse section 53
53. Leaf hair-points 0.2-0.6 mm long, coarsely and densely spinulose-denticulate; costae papillose on dorsal side 44. S. sinensiapocarpum

This species was described from China. In Asian Russia it is sporadically distributed in southern Siberia and in dry areas in the Caucasus. Grows at low elevations in xeric habitats athough sometimes collected along streams in Genuslly dry places, mostly on calcareous rocks. Its main diagnostic characters are reddish plants; long, terete, sharply, densely serrate leaf hair-points; partially bistratose leaf laminae; costae papillose on dorsal side; and subquadrate exothecial cells. See also comments under S. austrosibiricum.

Leaf hair-points up to 0.15 mm long, finely denticulate, or up to 0.7 mm long, sharply, distantly spinulose; costae smooth on dorsal side 54
54. Perichaetial leaves longer and narrower than stem leaves, 0.5-0.6 mm wide at base; capsules exposed laterally; leaf hair-points 0-0.2 mm long, narrow throughout, not decurrent; peristome teeth squarrose when dry 16. S. dupretii

A circumpolar montane species know in Russia from Murmansk Province, Karelia, Arkhangelsk Province and several localities in central and southern lowland provinces, rather frequent in Urals (from Subpolar to Southern), but absent in the Caucasus. It also has a scattered distribution in Asian Russia (southern Siberia, Taimyr, Yakutia and Kamchatka). Grows mainly on dry calcareous rocks; numerous collections in Murmansk were made on artificial substrates, i. e. , concrete constructions, or asphalt paths. It can be recognized by its small plants and leaves with unistratose laminae as well as short, narrow hair-points. Especially noteworthy are its long, narrow perichaetial leaves that cause the slightly furrowed capsules to appear exposed laterally rather than terminally.

Perichaetial leaves similar to stem leaves, 0.8-1.1 mm wide at base; capsules exposed terminally; leaf hair-points 0-0.7 mm long, widened at base, decurrent; peristome teeth erectopatent to patent when dry 36. S. pulchrum

Widespread circumpolar species with a mainly boreal distribution. In European Russia it is common in Murmansk Province, Karelia and Urals, but absent in lowlands and the Caucasus. S. pulchrum is the most common species of the genus in Asian Russia, especially in Taimyr and Yakutia. It is also fairly common in southern Siberia and Russian Far East, becomes rarer in Kamchatka and absent in Chukotka. Grows at low and middle elevations (up to 1950 m in Transbaikalia) in open places and under forest canopies on various types of dry or moderately wet rocks. Its diagnostic characters include medium-sized plants; mainly unistratose laminae with recurved margins; moderately long and distantly serrate hair-points, terete above and occasionally slightly flattened below; laminal cells with moderately thickened and ± sinuose walls; cylindrical capsules with subquadrate and transversely rectangular exothecial cells; and subentire to slightly perforate peristome teeth that are twisted and incurved inwards when dry.

55(51). Leaf margins recurved to near apices 56
Leaf margins plane in upper 1/5-1/2 57
56. Leaves 1.9-2.5 mm long; median leaf cells strongly sinuose; perichaetial leaves similar to stem leaves; leaf hair-points decurrent 40.S. robustum

Boreal mountain species known from Europe and North America. In Russia it is comparatively frequent in limestone areas in the Caucasus and was found once in South Urals. Grows in forest zone on open, shady limestone and dolomite rocks. Critical features for its recognition include unistratose leaf laminae; leaf cells with moderately thickened, strongly sinuose walls; strongly serrate and shortly decurrent hair-points; and elongate exothecial cells.

Leaves 1.2-1.7 mm long; median leaf cells slightly sinuose; perichaetial leaves oblong, different from stem leaves; leaf hair-points widened at base but not decurrent 46. S. subflaccidum

Rare species known from eastern Canada, mountain ranges of South and Central Europe and found once in the Russian Caucasus (Karachaevo-Cherkessia). The Russian plants grew at 2100 m a. s. l. on granite rocks in a flood valley birch forest. It can be recognized by its small plants; unistratose leaf laminae with recurved margins and slightly sinuose cell walls; rather long, terete, densely, sharply spinulose hair-points that are widened at base but not decurrent; and oblong exothecial cells.

57. Perichaetial leaves 0.5-0.6 mm wide at base, capsules exposed laterally 16. S. dupretii
Perichaetial leaves 0.6-1.25 mm wide at base, capsules exposed terminally 58
58. Leaf cells unistratose except 1-2 marginal rows of bistratose cells; perichaetial leaves widely acute; leaf hair-points short or absent 48. S. submuticum
(including subsp. arcticum)

A circumholarctic species occurring in mountains and lowlands. It is most frequent in lowland European Russia and Urals, sporadic throughout Asian Russia from the Arctic to southern Siberia. Grows mostly on calcareous rocks (limestone, dolomite, sandstone, gypsum) and often on artificial substrates (concrete, asphalt), occasionally on sand and fine soil at low elevations and in a variety of moisture and light conditions. The species can be recognized by its comparatively small plants; concave perichaetial leaves with oblong bases and absent or very short hair-points; and rectangular exothecial cells.

Upper leaf cells usually with bistratose patches or totally bistratose; perichaetial leaves narrowly acute; leaf hair-points present at least in upper and perichaetial leaves, short or long 59
59. Leaves with ridge-like plicae, often shouldered [S. brunnescens subsp. griseum]

This subspecies is known from Central and Southern Europe and southern areas in Scandinavia. It can be found in southern European Russia. It differs from type variety (see below) in having longer, shouldered, plicate leaves and stronger costae.

Leaves smooth, not shouldered 60
60. Leaf hair-points widened at base 61
Leaf hair-points narrow at base 62
61. Plants small, dull brown; leaves in straight rows or not in rows; leaf hair-points not decurrent; stem leaves 1.1-2.0 mm long 9. S. brunnescens subsp. brunnescens

This European species is known in Russia from a few localities in the Caucasus and Rostov Province. Grows in lowlands and the forest/subalpine zones in the mountains mainly on dry limestone and schist rocks; in Rostov Province it was collected on shell gravel. It can be recognized by its small, brown plants; partially bistratose upper leaf laminae; leaf cell walls almost esinuose; rather long, finely, densely scabrose hair-points that are widened at base but not decurrent, oblong exothecial cells; and strongly perforate peristome teeth.

Plants small to medium-sized, dark olivaceous or brownish; leaves occasionally in spiral rows; leaf hair-points decurrent; stem leaves 1.75-2.8 mm long 13. S. crassipilum
62. Leaves ovate-lanceolate, 2.2-3.0 x 0.5-0.8 mm long; leaf hair-points 0.3-1.0 mm long, distantly spinulose-denticulate; peristome teeth entire or lightly perforate 18. S. elegantulum

In Russia S. elegantulum is rather common in the Black Sea coastal area but infrequent in the mountains of Caucasus. There are a few records of it in lowland central provinces of European Russia as well as the Altai Mts. and it becomes more frequent in the southern parts of Russian Far East. Grows at low altitudes and in the forest zone in the mountains (up to 2000 m a. s. l. ) on calcareous rocks mainly under forest canopies. The combination of long leaves with flat upper margins; partially bistratose leaf laminae; short, almost esinuose leaf cells; long, narrow, distantly serrate leaf hair-points; long capsules with elongate exothecial cells; and subentire peristome teeth that are squarrose when dry greatly help to identify this species.

Leaves ovate-triangular, 1.75-2.6 x 0.6-0.9 mm long; hair-points 0-0.2 mm long, densely and coarsely spinulose; peristome teeth strongly perforate to cribrose 25. S. helveticum

A mainly European species known in Russia only from Dagestan Republic in Eastern Caucasus. Grows at low elevations on calcareous rocks in open places. Diagnostic features of this species include blackish plants; ovate-triangular leaves with very short, narrow, stiff, densely spinulose hair-points; almost completely bistratose upper leaf laminae; strongly thickened upper leaf margins; irregularly shaped exothecial cells; and strongly perforate peristome teeth.