Orthotrichiaceae. Genus Orthotrichum

1. Leaves hyaline hair-pointed 2

— Leaves not hyaline hair-pointed, sometimes with one or a few terminal hyaline cells (O. hyperboreum) 3

2.Leaves ovate, abruptly tapered to long, piliferous, hyaline hair-points; capsules smooth or weakly ribbed, not constricted below mouth when dry; exostome teeth 16 8. O. diaphanum

Orthotrichum diaphanum differs from other species of the genus in Russia in having the following combination of features: smooth, ovate leaves; leaf apices abruptly tapered to long, hyaline hair points; smooth or slightly striolate, cylindric capsules; 16 exostome teeth; and 16 endostome segments. It is widespread in Europe and Macaronesia from southern Scandinavia to the Canary Islands. In addition it is found in northern, eastern and southern Africa; western Asia, including the Caucasus; central and western North America; South America (Colombia, Ecuador, Uruguay) and Oceania (Hawaii). In Russia the species is common in the Caucasus, and until recently was known in European Russia only from Kalinin grad Province. But, the species has spread northward into European Russia and has been found the following provinces: in 1992, Volgograd; 2002, Rostov; 2006, Leningrad; 2008, Belgorod, Moscow and the Tatarstan Republic. Since its 2008 appearance in Moscow this species has been found in numerous localities, and is sometimes noticably abundant. In Russia it is a corticolous and saxicolous species growing on tree trunks and/or calcareous rocks.

— Leaves ovate-lanceolate, gradually narrowed to somewhat broad, trianglular, hyaline hair points; capsules strongly 8-ribbed, constricted below mouth when dry; exostome teeth 8-pairs 7. O. dagestanicus

This species was described from the xeric, montane areas of the eastern Caucasus, where it is fairly common at middle elevations (800–1600 m) on limestone as well as trees. It is also known from Kyrgyzstan (Ellis et al., 2015). Although originally described as having peristomes with 8 endostome segments, the study of additional collections of O. dagestanicum found that the peristome occasionally has 16 segments. Orthotrichum vittii F. Lara, Garilleti & Mazimpaka was reported from Dagestan Republic (Ellis et al., 2013), but the specimens were later re-identified as O. dagestanicum. Both species have hyaline hair-pointed leaves. But, O. vittii differs from O. dagestanicum in the following features: (1) capsule surface (weakly ribbed with shallow furrows, ribs slightly darker than capsules vs. strongly ribbed, with deep furrows, ribs reddish-brown); (2) exostome teeth number and stance when dry (8-paired to 16, reflexed to spreading vs. 8-paired, reflexed to appressed); (3) ornamentation on inner (ventral) surface of exostome teeth (distinctly papillose vs. nearly smooth); and (4) endostome segments (strongly appendiculate vs. not or slightly appendiculate). Additional noteworthy features of O. dagestanicum include leaf cells in part smooth, in part with low papillae; and immersed stomata moderately covered by subsidiary cells.

3.Exostome teeth erect or spreading at right angles to the capsule mouth when dry, striolate; endostome usually absent; calyptrae hairy; plants mostly saxicolous 4

— Exostome teeth reflexed or apressed to capsule wall when dry, papillose; endostome well developed; calyptrae naked or sparsely hairy; plants corticolous, rarely saxicolous 10

4.Capsules exserted2. O. anomalum

Orthotrichum anomalum can usually be recognized by the combination of exserted capsules with usually dark-red ribs, and exostome teeth that spread at right angles to the capsule mouth when dry. However, the species is variable and can sometimes be confused with O. pellucidum or O. hallii.But, the presence in O. anomalum of simple leaf cell papillae and unistratose leaf laminae will separate it from O. pellucidum with forked papillae and partly bistratose leaf lamina and O. hallii with bistratose leaf lamina. Orthotrichum anomalum is a calciphile and in Russia is widespread throughout all regions (except the high Arctic) where calcareous rocks occur. Although predominately a saxicolous species, it occasionally occurs on trees.

— Capsules immersed or emergent 5

5.Spores 37–43 mO. urnaceum]

This species has been attributed to Armenia and Azerbaijan (Ignatov et al., 2006) and may be found in the Russian Caucasus.

— Spores 14–17 m6

6.Endostome present, segments 8 or 16; vaginula densely hairy 20. O. urnigerum

This mostly European species is widespread in southern Scandinavia and known from a few localities in the mountains of mainland Europe. In Russia the species is known only from the western Caucasus (Teberda Reserve, Teberda River Valley) where it grows on cliffs at ca. 1320 m a.s.l. Orthotrichum urnigerum has been re­port­ed from the Republic of Karelia and Chukot­ka but these collections have not been verified. From closely related species (O. anoma­lum, O. pellucidum, O. cupulatum) O. urnigenum differs in having well developed endostomes with 16, rarely 8, segments; immersed or emergent, ribbed capsules; unistratose leaf laminae; and densely hairy vaginula. Blockeel (1987) considered O. urnigerum closely related to O. anomalum differing in having emergent rather than exserted capsules; densely hairy rather than sparsely hairy vaginulae; and endsotomes well developed with mostly 16 segments rather than occasionally present with 8 segments.

— Endostome absent, or rarely present, segments 8; vaginula naked or with 1–3 hairs 7

7.Capsules immersed to shortly emergent, cupulate, with 16 long ribs; exostome teeth 16; leaf cells with low papillae 6. O. cupulatum

Orthotricum cupulatum resembles O. urnigerum and O. pellucidum, but differs from them in having cupulate capsules with 16 long ribs. In constrast O. urnigerum and O. pellucidum have oblong-ovoid capsules with 8 ribs or 8 long and 8 short ribs. Orthotrichum cupulatum is a widespread holarctic species also reported from Mexico, South America, SE Australia, Tasmania and New Zealand. In Russia the species occurs in mountainous areas of the Caucasus, Urals, Altai, and Tyva Republic (Ignatov & Lewinsky-Haa­pa­saari, 1994; Fedosov & Ignatova, 2011). The species grows at low to high elevations on dry, exposed (rarely shady), calcareous rock outcrops.

— Capsules emergent, oblong-ovoid, with 8 long ribs, or at times with 8 long ribs alternating with 8 additional shorter ribs; exostome teeth 8-paired or only partly fused 16 8

8.Upper leaf lamina bistratose throughout, with many small, simple papillae; exostome teeth 8-paired 9. O. hallii

Orthotrichum hallii differs from other Russian Orthotrichum species in having the following combination of features: upper leaf cells bistratose throughout; leaf cells with low, simple papillae; capsules emergent; and exostome teeth papillose-striolate on the outer (dorsal) surfaces. In Russia O. hallii is restricted to the Altai and Tyva (Todzha depression) Republics (Fedosov & Ignatova, 2011). Outside Russia the species occurs in xeric areas of North America (Rocky Mountains from British Columbia to New Mexico), and a few localities in the Altai Mts of China and Kazakhstan. It grows on exposed rocks at moderate to high elevations.

— Upper leaf lamina unistratose or bistratose in patches, with low or high, simple or forked papillae; exostome teeth mostly 16 9

9.Plants not- or slightly glaucous; upper leaf cell unistratose; papillae mostly simple, low or high 2. O. anomalum

— Plants glaucous; upper leaf cells bistratose in patches; papillae mostly forked, high 13. O. pellucidum

Orthotrichum pellucidum is distinguished by the following combination of features: glaucous plants growing on calcareous rocks; upper leaf cells partly bistratose; capsules emergent with 8 strongly developed ribs; and 16 exostome teeth. In Russia O. pellucidum occurs in montane areas of the Subarctic that are usually xeric (Anabar Plateau, Chukotka, Magadan Province) but occasionally humid (Polar Urals), with isolated localities in the high mountains of the Altai and Eastern Sayan. Outside Russia the species is found in Svalbard, Greenland, the Arctic Archipelago of Canada and mountains of western North America from Alaska to Nevada (Lewinsky 1977, as Orthotrichum jamesianum Sull.). It grows on limestone rocks on xeric slopes in cool-steppe (tundra-steppe) environments mostly above or north of the timberline.

10(3). Endostome with 8 broad, papillose segments, fused above in a ring-like structure; immature capsules pyriform; Caucasus 3. O. callistomum

Orthotrichum callistomum is the only species in subgen. Callistoma (Z. Iwats. & Sharp) Lewinsky, a subgenus based on its unique endostome structure (Lewinsky, 1992). In addition to being fused at their tips the segments are densely papillose and have strongly projecting trabeculae on the inner (ventral) surfaces. Other distinctive features of the species include its pyriform immature capsules that are abruptly tapered (or puckered) to noticably small mouths (much like those of Ulota coarctata, but ribbed at nearly the entire urn length). Akatova et al. (2004) illustrated stomata in O. callistomum as superficial, while Lewinsky (1992) and Lewinsky-Haapasaari (1995) indicated the stomata were immersed and half-covered by subsidiary cells. Immersed stomata occur in Russian collections of this species but rare, while exothecial cells are arranged in a way simialar to superficial stomata (Fig. 84), causing confusions. In Russia the species is known from a single plant collected at ca. 1650 m alt. in the Kabardino-Balkarian Republic (Cherek Bezengijskij River Valley) growing on Salix caprea in a cushion of O. pallens (Akatova et al., 2004). The species occurs mainly in East Asia, in Taiwan, Sichuan, Yunnan, Xizang and Himalayas up to Nepal (Lewinsky, 1992). It was collected in Europe only once, in Swiss in 1849 (Bruch et al., 1850). Recently it was reported from north-east Turkey, where it was growing on Salix caprea andAlnus orientalis (Lara et al., 2010).

— Endostome with 8 or 16 segments, not fused above; immature capsules ovate to cylindric; various regions 11

11. Endostome segments 16, equal in length 12

— Endostome segments 8 or 16, if 16, then 8 long and 8 short segments alternate 14

12. Setae 0.8–1.2 mm long; capsules emergent or exserted; endostome segments weakly or not appendiculate 17. O. sibiricum

This species, described from the lower course of the Yenisei River, was synonymized with O. pallens by Lewinsky (1977). However, Fedosov et al. (2017b) now consider it a distinct species. Fedosov et al. (2009) reported it as O. holmenii Lewinsky-Haapasaari, a recently described species from Kazakhstan that is in need of further study. At present O. sibiricum is known from north-east European Russia (Nenets Aunomous District), Polar/Subpolar Urals, Central Siberia (Anabar Plateau), Yakutia (Orulgan Range) and Transbaikalia. The species typically grows on willow bark that is covered with silty alluvium, but is occasionally found on shaded calcareous sandstones and dry wood. Orthotricum sibiricum can be distinguished from all other Russian Orthotrichum species by the following combination of features: exserted, distinctly furrowed capsules; immersed stomata; exostome teeth 16, reflexed when dry; and endostome segments 16, papillose, ± equal in length. Orthotrichum scanicum differs from O. sibiricum in leaf apex margins (denticulate with teeth formed by emergent cell angles vs. entire or weakly crenulate due to protruding papillae); leaf cell papillae (simple vs. partly forked); setae length (ca. 0.3 vs. 0.8–1.2 mm long); and exothecial cell band width (2–3 cells wide (Lara et al., 2009) vs. mostly four). Orthotrichum hispanicum F. Lara, Garilleti & Mazimpaka is probably the species most similar to O. sibiricum. It was described from the Iberian Peninsula (Lara et al., 2000), and is also known from Turkey and Kashmir (Garilleti et al., 2009). Orthotrichum hispanicum and O. sibiricum have similar peristomes and both have simple as well as forked leaf cell papillae. It differs from O. sibiricum in having shorter (0.37–0.65 mm) setae; emergent capsules strongly constricted below the mouth; and smaller spores (11–15 mm). In contrast O. sibiricum has longer setae (0.8–1.2 mm long); exserted capsules indistinctly to moderately constricted below the mouth; and larger spores (13–20 mm).

— Setae 0.2–0.8 mm long; capsules immersed to shortly emergent; endostome segments strongly appendiculate 13

13. Exostome teeth short, 8-paired, never split; upper leaf margins entire 11. O. pallens (moravicum-morphotype)

Plants similar to O. pallens but differing in having 16 appendiculate endostome segments of equal length were described from eastern Europe as O. moravicum Plasek & Sawicki (Plasek et al., 2009). While revising Russian collections of O. pallens in MW a specimen from the Bashkortostan Republic was found that fully fits the description of O. moravicum but molecular phylogenetic evidence found the collection was not in a sister position to European collections of O. moravicum, but rather within the O. pallens clade, which is sister to O. moravicum. Thus, we treat O. pallens in a broad sense to include O. moravicum, highlighting, however, its possible separate status.

— Exostome teeth long, 8-paired below, split above; upper leaf margins uneven to crenulate-dentate 16. O. scanicum

Orthotrichum scanicum is treated here in a narrow sense (i.e. not including O. holmenii as was proposed by Medina et al., 2009). It is a rare montane, mostly European (southern Fennoscandia, mountains of central Europe and Mediterranean) species associated with mild climatic conditions. In Russia it is known from only two localities in the Caucasus (near Dombai, Teberda area, Karachay-Cherkessia Republic). The Caucasian collections of O. scanicum were growing on fir twigs at 1380–1600 m elev. Apparently it is a canopy-twig species: one collection came from the canopy of a fallen tree, the other was on a fallen twig in a fir forest (Ignatova et al., 2008). This area has a humid local climate that also supports other European Orthotrichaceae species, e.g. Ulota coarctata, Orthotrichum urnigerum, Pulvigera lyellii. Although O. scanicum was reported from the Khamar-Daban mountain range (Buryatia Republic) near Lake Baikal (Kazanovsky, 1991), these collections are so scanty they can not be confidently identified.

14(11). Plants somewhat glaucous; upper leaf cells with high, forked papillae; capsules emergent; calyptrae papillose, with papillose hairs; vaginulae naked 1. O. alpestre

Orthotrichum alpestre can be distinguished from the other species of the genus by the following combination of features: plants small; capsules emergent; stomata immersed; upper leaf cells with high, forked papillae; and endostome segments narrowly linear, with a spine-like uppermost cell. Orthotrichum alpestre is a widely distributed, saxicolous, montane species known from central and northern Europe (including Iceland and Svalbard), Turkey, the Caucasus, middle Asia, India, northern Pakistan, Japan, and widespread in western, but rare in eastern (Michigan, Labrador, Newfoundland, Greenland) North America (Lewinsky, 1977). In Russia O. alpestre is a rare species known from a few scattered localities in the Kola Peninsula, Polar and South Urals, the Caucasus, Altai Republic and Kemerovo Province (Salair Range). The species grows at various elevations but is more common in the upper forest belt, declining above timberline.

— Plants not glaucous; upper leaf cells mostly with low, simple papillae (occasionally higher, forked in O. hyperboreum); capsules immersed to emergent; calyptrae smooth, naked or rarely with a few smooth hairs; vaginulae naked or hairy 15

15. Vaginulae with numerous hairs 16

— Vaginulae naked or with a few (1–3) hairs 18

16. Vaginulae with short (0.2–0.5 mm long) hairs not emergent from perichaetia; calyptrae naked; spores furrowed [O. stellatum]

This suboceanic, amphiatlantic species was reported from Georgia (Ignatov et al., 2006), and may occur in the humid Black Sea coastal areas of Russia. It can be recognized by the following combination of features: vaginulae with numerous, short, smooth hairs; leaves lanceolate; capsules 8-ribbed, ribs dark-red, contrasting strongly with other exothecial cells; stomata usually covered by broad, prominent subsidiary cells (Lara et al., 2009).

— Vaginulae with long (ca. 1 mm long) hairs emergent from perichaetia; calyptrae sparsely hairy; spores papillose 17

17. Capsules emergent, cylindric, mostly contracted below mouth, gradually narrowed to setae; capsule necks distinctly differentiated; exothecial ribs extending to the whole length of the urns 18. O. stramineum

Orthotrichum stramineum is similar to O. pallens, but its plants are larger; calyptrae sparsely hairy rather than naked; vaginula hairy rather than naked or with a few hairs; and capsule necks are better developed. The species is widespread and locally common in Europe, especially in Britain, south Scandinavia and the Alps, but becomes gradually less common to the east. In North America the species has been reported only from Newfoundland. In Russia O. stramineum is known from Kaliningrad Province and the Caucasus where it grows on beech, pear and fir at middle elevations, 1200–1600 m.

— Capsules mostly immersed, oblong-ovate or fusiform, somewhat narrowed below mouth, sharply narrowed to setae; capsule neck not differentiated; exothecial ribs only in upper third to half of capsules 12. O. patens

Orthotrichum patens is mostly a Scandinavian and Central European species. In Russia it is known from Kaliningrad Province and the southern Black Sea coastal area where it grows on tree (mostly oak, pear, poplar) trunks. It can be recognized in the field by its immersed, oblong-ovate or fusiform, strongly ribbed (but only in the upper parts) capsules. These capsules in conjunction with its hairy calyptrae, hairy vaginulae and immersed stomata that are almost fully covered by subsidiary cells separate it from O. pallens.

18(15). Spores 17–28 mm; capsules gradually narrowed to setae; neck moderately differentiated; endostome segments stout, at least some erect when dry 15. O. rogeri

In Russia O. rogeri is restricted to the Altai Mountains where it grows only on the trunks of Padus asiatica in association with Nyhol­miella obtusifolia, Lewinskya sordida, L. speciosa and L. vladikavkana. The species favors mild climatic conditions and is found at moderate elevations in the valleys of mountain forests. Otherwise it is a relatively rare species known from a few localities in southern Scandinavia, central and southern Europe, the Caucasus (Georgia and Azerbaijan), and northern India (Kashmir). Orthotrichum rogeri is characterized by its obtuse leaves; stomatal crypts nearly covered by projecting subsidiary cells; large spores; moderately differentiated capsule necks; and mostly stout segments that are erect when dry. Lara et al. (2009a, b) also noticed dimorphism of male and female branches (the latter have nearly twice larger leaves). Although throughout its range spore size varies somewhat, collections from the Altai Mts. have spores in the 25–28 mm range.

— Spores 10–18(–22) mm; capsules sharply narrowed to setae; neck not differentiated; endostome segments narrow, incurved when dry 19

19. Leaf margins plane or slightly recurved on one side 4. O. consobrinum

Orthotrichum consobrinum is predominantly an East Asian taxon present in Japan, China, Korea and the Russian Far East; it was recently discovered in Spain and Turkey (Lara et al., 2009b). In Russia it occurs in southern Primorsky Territory at low to moderate elevations growing on fir, alder, maple and other broad-leaved trees. It is distinguished from all other Russian Orthotrichum species in having nearly plain leaf margins, an extremely rare character state in the genus. However, the same character state is present in the poorly known O. microcarpum De Not. which occurs in Georgia (cf. Ignatov et al., 2006). As discussed by Lara et al. (2009a, b), O. consobrinum differs from O. microcarpum in the following ways: leaf stance when dry (erect-appressed to somewhat flexuose vs. flexuose to often contorted); leaf apices (acute or mucronate vs. obtuse to acute, never mucronate); stomatal crypts (half to completely covered by projecting subsidiary cells vs. slightly covered by projecting subsidiary cells); and endostome segments (high, rugulose to slightly papillose vs. low, striolate). Orthotrichum consobrinum resembles O. pallens in this aspect but differs in having plane leaf margins and stomatal crypts nearly completely covered by projecting subsidiary cells.

— Leaf margins strongly recurved on both sides for almost the entire leaf length 20

20. Leaves (at least below) ovate-lanceolate to ovate; leaf apices mostly rounded, rarely broadly obtuse to acute 21

— Leaves lanceolate; leaf apices acute or bluntly rounded 22

21. Capsules immersed to emergent; upper leaf cells papillose; stomatal crypts half-covered by projecting subsidiary cells 5. O. crenulatum

Orthotrichium crenulatum is primarily a central Asian speciesknown from Afghanistan, Pakistan, Kyrgyzstan, Kazakhstan, southern Siberia, northern India (Kashmir), Turkmenistan, western Tibet, and also disjunct in Japan (Lewinsky, 1992; Ellis et al., 2014; Suzuki, 2014). In Russia it occurs mostly on Ulmus pumila in xeric areas of Transbaikalia and Buryatia with one isolated north Siberian (Anabar Plateau) locality in flood plains growing on willow and poplar trunks (Fedosov et al., 2017b). Orthotrichum crenulatum is a remarkably distinct species because of its peculiar dark-green color; ovate to ovate-lanceolate leaves with rounded or broadly acute apices; broadly recurved to revolute leaf margins; and stomatal crypts half-covered by projecting subsidiary cells. However, Russian specimens differ from most Asian specimens in having unistratose rather than partly bistratose leaf cells. There are odd specimens of O. crenulatum from the Republic of Buratya with mostly acute upper leaves, but their lower leaves are typical for the species. Orthotrichum crenulatum is morphologically similar to O. pamiricum Plasek & Sawicki, which also has unistratose leaf cells, but O. pamiricum differs in having 16 endostome segments (Plaseket al., 2014). Orthotrichum rivulare Turner, which grow along streams in western Europe and western North America, is similar to O. crenulatum in having somewhat broadly ovate leaves with rounded apices. But that species has 16 endostome segments and papillose calyptrae. In contrast O. crenulatum has 8 endostome segments and smooth calyptrae. In addition, plants of O. rivulare are considerably more robust than plants of O. crenulatum (1–2 vs. 0.3–0.6 cm high). Nevertheless, morphologically the group is vaguely delimited and clearly in need of revision.

— Capsules emergent to slightly exserted; upper leaf cells smooth; stomatal crypts almost completely covered by projecting subsidiary cells [O. sprucei]

Orthotrichum sprucei Mont. was endemic to western Europe until Bruce Allen found it in Kazakhstan (see Goffinet, 2002). It seems likely the species will also be discovered in Russia. For detailed discussions and illustrations of O. sprucei see Lewinsky (1995) and Goffinet (2002).

22. Leaves with short, blunt, canaliculate apiculi 19. O. tenellumserif">serif"

The world distribution of O. tenellum is presently unsettled. All agree it occurs in western Europe, Macaronesia, northern Africa, and western Asia to the Caucsus and Turkey. Vitt (2014) attributes the species to the Pacific coast of North America (British Columbia to California), but others exclude North America from its range. In Russia the species has been collected twice in the Black Sea coastal area near Sochi. In 1977 it was collected on Lagerstroemia indica in a dendrarium near the town of Sochi and in 2003 (in nearly the same area) it was collected on beech (Fedosov et al., 2017b). There is a report of the species from Leningrad Province (Sofronova et al., 2014), but that specimen was not examined in this study. The outstanding, diagnostic feature of O. tenellum is found in its leaf apex which is abruptly narrowed to a knob-shaped, blunt, canaliculate apiculus. Other important features of the species include small upper leaf cells; long, narrow, emergent capsules; stomatal crypts almost completely covered by projecting subsidiary cells; exostome teeth in 8 pairs; endostome segments 8; and calyptrae naked. Orthotrichum pumilum, O. rogeri, and O. scanicum are morphologically similar to O. tenellum. But, they differ in the following ways: O. pumilum has acute, apiculate leaves and larger leaf cells; O. rogeri has larger spores and stout endostome segments; O. scanicum, although having long-cylindric capsules and occasionally canaliculate leaves, has 16 exostome teeth and 16 endostome segments (8-paired exostome teeth, and eight endostome segments in O. tenellum).

— Leaves with acute to apiculate, rarely obtuse apices 23

23. One or few cells at leaf apices hyaline; margins near apex crenulate-dentate; upper leaf cells with simple and forked papillae; plants saxicolous; Asi­an Arctic and Subarctic 10. O. hyperboreum

Orthotrichum hyperboreum can be recognized by the combination of hyaline, crenulate-dentate leaf apices (easy to see in the field); leaf cells with simple and forked papillae; naked calyptrae; and saxicolous habitat. From Orthotrichum pallens it differs in crenulate-dentate vs. entire leaf apex; and hyaline vs. green apical cell(s); and saxicolous vs. corticolous growth. Orthotrichum hyperboreum is similar to Zygodon in having leaves with a hyaline apical cell. But, Zygodon has exserted capsules and cucullate calyptrae while O. hyperboreum has immersed to emergent capsules and campanulate calyptrae. Fedosov et al. (2017a) recently described this species from Central Siberia (Anabar Plateau). It seems to be widespread in the montane Arctic and Subarctic areas of Asia: not rare in some areas of the Anabar Plateau and the Polar Urals with single localities in the Taimyr Peninsula (Byrranga Range) Yakutia (Orulgan Range, Ust’-Maja District) and Chukotka. Typically the species grows in moist, shaded rock (basaltic, dolerite, andesite, gneiss, gabbro and dunite) niches in the upper forest belt and above or northward of the timberline up to 1500 m a.s.l.

— Leaf apices concolorous, margins entire; upper leaf cells with simple papillae or nearly smooth; plants corticolous; cool temperate to hemiboreal, mostly in European Russia, Caucasus and Altai 24

24 Upper leaf cells 12–19 mm wide; leaves usually apiculate; stomatal crypts almost completely covered by projecting subsidiary cells; endostome segments mostly 8 14. O. pumilum

This widespread species has been reported from most European countries; North Africa and the Canary Islands; European Russia, Middle Asia, southern Siberia, eastern China and Japan. In North America the species occurs throughout the United States (except the Pacific northwest and southeastern states) and in southernmost Canada (except British Columbia). In Russia O. pumilum is found in Middle European Russia, (western provinces and eastward to Vologda, Ivanovo, Vladimir, Volgograd Provinces), throughout the Russian Caucasus, and isolated localities in the southern Urals and Altai. The most common habitat for this species is deciduous tree bark, but it occasionally is found on rocks. In forested areas it is especially abundant in towns/cities, and in montane areas it occurs at low to moderate elevations. Orthotrichum pumilum can be recognized by the combination of broad, mostly apiculate leaves; upper leaf cells with low papillae or nearly smooth; capsules immersed to emergent; exostome teeth 8-paired; endostome segments 8; stomatal crypts strongly covered by projecting subsidiary cells; naked vaginulae; and calyptrae naked or with sparse, smooth hairs. Orthotrichum pumilum resembles O. pallens, but that species differs from O. pumilum in having narrower leaves with smaller upper leaf cells, and acute or obtuse apices; 16 endostome segments; and stomatal crypts half-covered by projecting subsidiary cells. Orthotrichum schimperi Hammar and O. philibertii Venturi are European species that also have apiculate leaf apices. Indeed, O. schimperi is sometimes considered conspecific with O. pumilum, but it differs in having shorter setae (0.1–0.3(–0.4) vs. 0.3–0.6 mm long) and upper leaf cells bistratose in patches rather then completely unistratose. Orthotrichum philibertii differs from O. pumilum in having calyptrae with papillose hairs rather than naked or with smooth hairs and exostome teeth pale-yellow rather than dark orange to orange-brown.

— Upper leaf cells 9–14 mm wide; leaves acute or obtuse; stomatal crypts half-covered by projecting subsidiary cells; endostome segments mostly 16 (8 long, 8 short) 11. O. pallens

Lewinsky (1977) gave the distribution of this species as throughout Europe, Middle Asia, Pakistan, northern India, southern Siberia, Japan and scattered localities throughout North America including the Canadian Arctic Archipelago, and Greenland (not mapped in Vitt, 2014) southward to Mexico. It is also known from the paramo of Venezuela (Lewinsky & Griffin, 1986). Based on recent molecular-phylogenetic evidences, some Russian collections previously placed in O. pallens are now treated as O sibiricum or O. hyperboreum. Orthotrichum pallens can be recognized by the following combination of features: leaf apices acute to obtuse; leaf margins plane, entire above; upper leaf cells papillose; capsules emergent; stomata immersed; stomatal crypts nearly free of projecting subsidiary cells; exostome teeth 8-paired, never splitting into 16 teeth; endostome segments 16; and calyptrae naked or nearly naked, sharply plicate. The exact world distribution of O. pallens is uncertain because of recent changes in the understanding of the species. In Russia the distribution of O. pallens is similar to that of O. pumilum: western provinces of European Russia, throughout the Caucasus, the Bashkortostan Republic and the Altai Mountains (see Ignatov & Lewinsky-Haapasaari, 1994). Russian Arctic collections, at present named O. pallens, are in need of further examination before they can be reliably identified. Records of O. pallens from Greenland (Lewinsky, 1977), Svalbard and the Arctic Archipelago of Canada are also in need of further examination; they may represent either O sibiricum or O. hyperboreum. Orthotrichum pallens usually grows on poplar, apple, maple, pear, alder, or lime trees and occasionally occurs on concrete or rocks. It is especially common in towns and cities growing on single trees or open tree stands. In the Altai Mountains O. pallens was found in the subalpine belt (ca. 2100 m) in a fell-field at the base of Ribes odorata.