Brachythecium coruscum, I.Hagen, 1908

Draper, Isabel, Mazimpaka, Vicente & Hedenäs, Lars, 2014, Molecular and morphological circumscription of Brachythecium coruscum as a separate taxon from Brachythecium albicans (Brachytheciaceae, Bryophyta), Phytotaxa 158 (2), pp. 182-194 : 187-188

Description of Brachythecium coruscum

Brachythecium coruscum I. Hagen (1908: 3). ≡ Brachythecium salebrosum var. coruscum (I. Hagen) C.E.O. Jensen in Weimarck (1937: 48). ≡ Brachythecium salebrosum subsp. coruscum (I. Hagen) Jensen (1939: 422). Type:— NORWAY. Oppland: Lom, Jotunheimen, in monte Vesleloftind. UTM WGS84 (MP 53–55, 34–35) 1518 II,

ca. 1400 m o.h., 0.8.1890, Chr. Kaurin & E. Ryan (holotype TRH-163169!, isotypes O-8921!, O-8922!, S- B141037!). = Hypnum albicans var. groenlandicum C.E.O. Jensen (1898: 437) . ≡ Brachythecium albicans var. groenlandicum (C.E.O. Jensen) Paris (1900: 41) . ≡ Brachythecium groenlandicum (C.E.O. Jensen) Schljakov (1952: 221) . Type:— GREENLAND: Hold with Hope, N. Hartz; Scoresby-Sund: Danmarks-Ø, N. Hartz; Gaasefjord, N. Hartz; Kobberpynt, N. Hartz; Rund-Fjeld, N. Hartz; Cap Stewart, N. Hartz (syntypes, probably in C, n. v.; the two taxa were synonymized by Nyholm, 1965).

Plants medium to frequently large (shoots 0.8–2.0 mm wide), in dense or scattered mats, pale or yellowish-green to golden, sometimes brownish in old parts. Stems decumbent, up to 5(–7) cm long, sparsely and irregularly branched, sometimes pinnately so; transverse section more or less rounded; central strand very narrow, irregular, few cells narrow and thin-walled; basic tissue regular, 3–5 concentric layers of large and thin-walled cells; cortex with 2–4 concentric strands of brownish, thick-walled and almost isodiametric cells; hyalodermis lacking. Branches erect, straight or curved, 0.5–2.5(3.0) cm long, 0.7–0.8(1.0) mm wide. Rhizoids in tufts, inserted near leaf insertion in creeping stems, scarcely or not branched, smooth, brown. Paraphyllia lacking. Pseudoparaphyllia foliose, broadly obtuse. Axillary hairs 1–3 in most leaf axils, 2–3 celled, basal cell brown, upper ones hyaline, uppermost one 32–67 × 8–14 µm. Leaves on stems and branches loosely imbricate, erect, flexuose when dry but sometimes strongly wrinkled, erect-patent when moist. Stem leaves narrowly to broadly ovate or ovate triangular, 1.7–2.5 × 0.7–1.1 mm, narrowed at insertion, upwards narrowed from 1/4–1/3 to apex, generally abruptly tapering to a broad acuminate apex, acumen 1/5 leaf length, denticulate; base long decurrent through a progressively narrowing wing (6)8–15 cells long. Lamina concave, strongly plicate; margin unbordered, often with narrow rectangular cells in lower part; predominantly plane, sometimes narrowly recurved on lower leaf third of one or both sides, or on acumen base, entire or, rarely, finely denticulate near apex and in acumen; costa generally single and extending 40–70% of leaf length, sometimes shortly forked above or branched from base, stout at base and middle but turning weak in upper third, 50–68 µm wide at base, in transverse section plane-convex (ventral side almost plane, dorsal side convex to rounded), with cells large and thick-walled, more or less uniform; basal lamina cells shortly rectangular, 20–30 × 8–10 µm, incrassate, smooth, alar cells almost isodiametric-rhomboid or quadrate to shortly rectangular, 17.5–30(35) × 7.5–12.5(15) µm, incrassate, eporose; alar group triangular, plane or slightly excavate, composed of 5–10(13) cell columns, marginal ones ascending along margin, 8–11(15) cells high, inner columns 3–5 cells high; mid-leaf cells (40)44–65(75) × 5–8 µm, linear, gradually tapering to acute ends, smooth, slightly incrassate; upper leaf cells linear, (45)50–75(80) × 5.0– 7.5 µm, gradually tapering to acute or long acute ends, slightly incrassate and smooth. Branch leaves similar to stem ones but often ovate-lanceolate and smaller, 1.5–2.0 × 0.4–0.6 mm, with margins generally denticulate, sometimes falcato-secund. Brood bodies lacking.

Dioicous. Perigonia laterally inserted on stem; perigonial leaves broadly ovate, gradually or suddenly narrowing to a fine acumen up to 1/3 leaf length, not plicate; margin unbordered, sometimes with narrow rectangular cells in lower half, plane; costa absent; lower lamina cells linear, shorter than upper ones, smooth, not incrassate; upper cells linear, smooth, not incrassate; anteridia numerous, well developed; paraphyses few, 6–10 cells long. Perichaetia laterally inserted on stem; inner perichaetial leaves erect to erecto-patent or patent; basal leaf ovate to broadly ovate, gradually or suddenly narrowing to a long acumen that sometimes reaches up to 50% of whole leaf length; not plicate; margin plane, unbordered; costa usually absent, when present single; basal cells rectangular, shorter than upper ones, 34–44 × 10–14 µm, smooth, thin-walled; upper leaf cells linear, smooth, not incrassate; archegonia 2(–3), sometimes numerous, well developed; paraphyses abundant, 6–17 cells long. Sporophytes not seen.

Distribution and habitat:— Brachythecium coruscum is an arctic-boreal species ( Dierssen 2001), mainly distributed in Greenland, Iceland, the central and northern mountains of Sweden and Norway, in Canada and Alaska ( Duell 1985, and material in S!). It has been also collected in northeast Russia ( Duell 1992, and material in S!) and Turkey (material in S!). In most localities, it forms dense mats on moist rocky surfaces, on sheltered or exposed soil in rocky terrains, in heaths or in alpine meadows. It has been found at a wide range of elevations, from 200 m in Norway, to 2100 m in Turkey.