Orthothecium rufescens (Dicks. ex Brid.) Bruch, Schimp. & W. Gümbel, Bryol. Eur.

8. Orthothecium rufescens (Dicks. ex Brid.) Bruch, Schimp. & W. Gümbel, Bryol. Eur. View in CoL 5: 107. 1851.

— Hypnum rufescens Dicks. ex Brid., Muscol. Recent. 2(2): 139. 1801. Fig. 25 A, H View Fig , 26 A–B, D–E View Fig .

Description: Plants large, cherry-red, moderately to slightly glossy when dry. Stems procumbent to ascending, 2–10 cm long, irregularly branched. Leaves erect-spreading, often slightly secund, 2.0–4.5×0.5–1.0 mm, narrowly lanceolate-triangular, tapering from near base to long and narrow acumen, scarcely narrowed to insertion, “truncate” at base, with small and sharp rounding at leaf angles, not decurrent, weakly concave, strongly plicate; margins narrowly recurved almost from base at most of leaf length; cells in mid-leaf 50–150×5–8 (–10) µm, with moderately thickened, weakly porose walls; basal leaf cells shorter and wider, thick-walled, porose, alar cells not differentiated. Specialized asexual reproduction by axillary gemmae rarely present. Sporophytes rare, unknown in Russia. Setae 2–3.5 cm long. Capsules ca. 3 mm long, cylindrical, erect or slightly inclined, straight or almost so. Opercula highly conic to shortly rostrate. Annulus revoluble. Peristome ± reduced: exostome teeth narrow, pale, striolate below on dorsal surface, finely papillose above; endostome basal membrane 1/4 of peristome height, segments narrow, cilia absent or rudimentary. Spores 10–14 µm [sporophyte features based on material from Scandinavia and the European Alps].

Distribution and ecology. Orthothecium rufescens is known from most European countries, Caucasus and Western Asia. In Russia it was reported from many areas, including the Arctic; however, these records were based on misidentifications of O. chryseon . Orthothecium rufescens only occurs in few localities in the Russian part of Caucasus and in a single locality in NW European Russia. We also confirm its occurrence in North Urals (Perm Province). In Caucasus it occurs in the alpine zone, being abundant at places on wet, shady calcareous rocks, near entrances into karst caves, etc. In Karelia it was also collected on wet calcareous cliffs near a waterfall.

Specimens examined: EUROPEAN RUSSIA: Karelia: Kuusamo, Paanajärvi, Kulmakkapuro, 31.VIII.1933, Kotilainen s.n. (LE); same place, Sovajärvi, 8.VIII.1936, Kotilainen s.n. (LE). Perm Territory: Chusovskoy Distr., left bank of Chusovaya river, 16.VII.2017, Bezgodov 213 (MW 9090558).

EUROPE: Romania: Transsilvania, distr. Năsăud, 2.VII.1918, Peterfi s.n., Flora Romaniae Exsiccata #1136 (MHA 9066913). Slovakia: mont. Mala Tatra, prope Terchova, IX.1988, Pilous s.n. (MHA 9066909). Poland: Tatra Mts, SW of Zakopane, 10.III.1995, Ignatov & Ochyra s.n. (MHA 9066910). Switzerland: Neuchâtel, 29.IX.2017, Hedenäs s.n. (S, B262945). Austria: Schneeberg Mt., Ignatov & Schanzer 05-5007 (MHA 9066911); Salzburg, VIII.1907, Klaus s.n., E. Bauer, Musci europaei exsiccati #591 (MW 9091881). Croatia: Plitvice, 20.IV.1954, Een Cr044 (S, B22282). France: MidiPyrénées Province, Hautes-Pyrénées, 4.VIII.1959, Een F367 (S, B33705); Germany: Bayern, VII.1886, Haussknecht s.n. (S, B289705). Italy: Lombardia, Como, 4.VIII.1895, Artaria s.n. (S, B214468). Norway: Nord-Trøndelag, Røyrvik, 19.VII.2014, Hedenäs s.n. (S, B205394). Sweden: Dalsland, Dalskog, 25.X.1975, Hallingbäck TH 44309 (S, B217040); Torne lappmark, Jukkasjärvi, 10.VIII.1983, Hedenäs s.n. (S, B295979); Pite lappmark, Arjeplog, 16.VII.1932, T. & A. Arwidsson s.n. (S, B113369). United Kingdom: Scotland, 27.VII.1956, Een UK184 (S, B24278).

Differentiation and variation. Orthothecium rufescens is somewhat similar to O. chryseon in leaf shape and a strong plication, which has caused confusion. However, they differ in habit: O rufescens always has stiff, erect-spreading, often somewhat secund leaves, which are gradually tapered almost from the base, whereas the leaves of O. chryseon are loosely appressed, softer, never secund, and ovate-lanceolate. Furthermore, the recurvation of leaf margins in O. rufescens ends slightly above the leaf insertion, so small portion in the leaf angles are flat, whereas in the leaves of O. chryseon the margins are recurved to the lowermost leaf portion, including the short decurrencies. Also, the leaves of O. rufescens are longer acuminate.

One enigmatic specimen, O. aff. rufescens, OK2276 , collected on wet cliffs in the subalpine zone of Altai, was resolved as O. rufescens in the ITS analysis, and among O. intricatum accessions in the plastid tree. It is intermediate in morphology: the leaves are the largest among O. intricatum included in this study ( Fig. 25H View Fig ), but unlike O. rufescens ( Fig. 26A,D View Fig ) the leaves in the Altaian plants are appressed to somewhat erect ( Fig. 26B, E View Fig ), similar to some plants of O. intricatum , especially those from the eastern part of its Eurasian distribution ( Fig. 26C, F View Fig ) and unlike western populations, where the leaves are homomallous-spreading ( Fig. 26G, H View Fig ). They are terete in the specimen from Altai.