Orthothecium chryseon Bruch, Schimp. & W. Gümbel,

3. Orthothecium chryseon Bruch, Schimp. & W. Gümbel, Bryol. Eur. 5: 107. 1851. Figs. 8A–J View Fig ; 9D–E View Fig .

Description: Plants large, goldish-, brownish- or reddish-green, occasionally bronze or intense wine-red, glossy, in dense or loose tufts. Stems procumbent, ascending or erect (especially when growing in large, dense cushions), to 10 cm long. Leaves erect-spreading in upper parts of stems, appressed below, 2.1–2.9×0.8–1.0 mm, ovate-lanceolate or ovate-triangular, short or long acuminate, upper part of narrow acumen straight, flexuose or, occasionally, in some leaves recurved or incurved at right angle, moderately concave, strongly plicate, slightly and gradually narrowed to insertion, very shortly decurrent; margins narrowly recurved from base and at most of leaf length; cells in mid-leaf 60–85×5–6(–7) µm, thick-walled, porose; basal leaf cells shorter and wider, strongly porose, alar cells not differentiated. Specialized vegetative reproduction unknown. Sporophytes rare. Setae 2.5 cm. Capsules pale, 2.5 mm long, cylindrical, erect, straight or slightly curved. Opercula conic, with small apiculus. Annulus revoluble. Peristome ± perfect; exostome teeth pale, striolate below on dorsal surface, papillose above; endostome basal membrane high, segments wide, cilia to 1/2 of segments length. Spores 11–16 µm.

Distribution and ecology. Orthothecium chryseon has a broad arctic-alpine distribution. It is common in the Arctic, and in the high-Arctic region sometimes abundant or at places even dominating in tundra vegetation, e.g. in the Franz-Josef Land and Novaya Zemlya archipelagos. It occurs in various kinds of tundra vegetation north of the forest limit but is most frequent and abundant in areas with calcareous bedrock. In permafrost areas of Siberia O. chryseon is a constant component of rich fen vegetation, associated with Paludella, Tomentypnum, Cinclidium, Catoscopium , etc., it is not rare in nival communities, near melting snow beds, on brook banks, and hanging mires on steep slopes. In more southern regions, O. chryseon occurs only in the alpine to subnival belts of the mountains: Alps and Western Carpathians in Europe, Caucasus in Armenia. In all mountains of southern Siberia, it occurs in the alpine zone with tundra vegetation, but is more common on wet cliffs at all elevations; it occurs in Mongolia, but is absent from China, Japan, Korea, and most of the southern areas of the Russian Far East, where it is absent in continental area south of the Amur River and the Kuril Islands, although having a few localities in Sakhalin. In North America it extends southwards to Colorado. Contrasting with the wide distribution in Asian Russia, the southern limit of O. chryseon in European Russia is quite northern: the southernmost localities are in northern Karelia and in the Sub-Polar Urals in the Republic of Komi. In Europe, O. chryseon occurs in the Scandinavian countries, Iceland, and Central Europe where it is a rather rare species of the highest locations in the Alps and Western Carpathians. Plants with sporophytes are occasionally present in northern Scandinavia, but they are very rare in Russia: we collected them only once on a wall of rather soft schistose cliff with permanent seepage from melting permafrost, where the species formed a pure carpet.

Additional selected specimens examined: EUROPEAN RUSSIA: Republic of Komi, upper course of Grube-yu Creek, 14.VIII.1932 Govorukhin s.n. (MW 9050846). ASIAN RUSSIA: Yamalo-Nenetsky Autonomous Area, Polar Urals, Khadata Lake, 5.VIII.1964 Filin s.n. (MW 9050848). Altai Republic: Kosh-Agach District, Taldura River, Ignatov & Ignatova 12-391 (MHA). Krasnoyarsk Territory: Severnaya Zemlya Archipelago, Sergey Kamenev Island, 26.VIII.1932 Savicz 805 (MHA 9018699); Taimyr Peninsula: Afanasiyevskie Lakes, Fedosov 06-13 (MW 9050858); Kotuykan River 4 km downstream Arbyn Creek mouth, Fedosov 11-1265 (MW 9050856); Maimecha River, Fedosov 09-173 (MW 9050863); Medusa Bay, Willem Barents biostation, 24.VII.2003 Varlygina s.n. (MW 9050860); Syrutaturku Lake, Pospelova 94/75 (MW 9049061); Byrranga Range, Bolshaya Bootankaga River, 16.VII.1991 Kuvaev 1786 (MW 9049055); Putorana Plateau, Glubokoe Lake, Fedosov 15-0869 (MW 9050852); Putorana Plateau, Ayan Lake, 16.VIII.1983, Czernyadjeva 123 (LE). Yakutia: Oymyakon Distr., Suntar-Khayata Mt. Range, Mus-Khaya Mt., Ignatov & Ignatova 11-3167 (MW 9049082); Tomponsky Distr., Sette-Daban Range: Segenyakh (Rosomakha) Creek, Ignatov & Ignatova 15-531 (MW9049086); western slope of Okraina Range between Ulakh and Nadezhda Creeks, Ignatov & Ignatova 16-887 (MHA 9022490); Momsky Distr., Ulakhan-Chistai Mt. Range, middle course of Tirekhtyakh River, Ignatov & Ignatova 18-1575 (MHA 9027967). Chukotka: Krest Bay, Egvekinot Settlement, 26.VII.1969 Afonina s.n. (MW 9049091); Ioni Lake, 30.VI.1977 Afonina s.n. (MW 9049090); Bilibino Settlement, Afonina s.n., Bryophyta Rossica et Civitatum Collimitanearum Exsiccata, Fasc. V (2004) №152 (MW 9049089); Anadyr River basin, upper course of Yablon River, 7.VIII.1982 Afonina s.n. (LE); Anadyr Distr., upper course of Tanyurer River, Bezymyannoe Lake, 11.VII.1979 Afonina s.n. (LE); Vrangel Island, Somnitel’naya Bay, 18.VIII.1985 Afonina s.n. (LE). Kamchatsky Territory: Northern Koryakia, Pekul’neyskoe Lake, 15.VIII.1984 Afonina s.n. (LE). Irkutsk Province: Usol’sk Distr., Kitoy River at Razdol’e Settl., 17.IX.1975, Safronova s.n. (LE). Buryatia: Oka District, Eastern Sayan Mts, Kitoy Range, upper course of Kitoy River, 15.VIII.1960 Bardunov s.n., Bryophyta Rossica et Civitatum Collimitanearum Exsiccata, Fasc. IX (2012) #380 (MHA). Khabarovsk Territory: Verkhnebureinsky Distr., Bureinsky State Reserve, Ignatov 97-331 (MHA 9018695). Sakhalinskaya Province: Sakhalin Island, East-Sakhalin Mountains, Balagan Mt., Bakalin D#S-26-3-17 (MW9078378).

NORWAY: Svalbard, Hornsund, Godzik & Grodzinska s.n., Bryophyta Svalbardensia Exsiccata, Fasc. IV (1987) №80 (MHA 9066908); Alpen Dovrefjeld, auf Felsen des Berges Knutsho, 24.VII.1907, Bryhn s.n., E. Bauer, Musci europaei exsiccati #590 (MW 9050841). FINLAND: Kuusamo, Paanajärvi, Kuoppaoja, Brotherus s.n., Bryotheca Fennica 261 (MW9050842). SWEDEN: Lule Lappmark, Kvikkjokk, Ruotnas, 2.IX.1837, J. Ångström (S, B32126); Jämtland, Åre, Silverfallet, 27.VIII.2011, Hallingbäck TH 5661 (S, B217019); Jämtland, Undersåker, Norder-Tväråklumpen, Nordostbranten, 25.VII.2002, Weibull TH 38249 (S, B217013); Torne lappmark, Jukkasjärvi, Kärketjårro, 19.VII.2005, Hallingbäck TH 43113 (S, B217014).

Differentiation and variation. Orthothecium chryseon was most frequently misnamed in herbarium collections as O. rufescens . It is likely that the two large Orthothecium species common in Asian Arctic, i.e. O. chryseon and O. retroflexum , were assumed by bryologists as different, and having at hand two available names, i.e. O. rufescens and O. chryseon , they applied these names in a wrong way: O. chryseon was called O. rufescens , while O. retroflexum was called O. chryseon . Distinctions from O. rufescens and O. retroflexum are discussed under those species. Orthothecium brunnescens was also identified as O. chryseon due to a large size of plants; however, the former species has acute rather than acuminate leaves which are scarcely plicate and often homomallous to almost falcate-secund, while leaves of O. chryseon have narrower acumina, they are strongly plicate and terete, always erect to loosely appressed, with straight or flexuose, only occasionally (more often at shoot tips) curved at right angle is some leaves.