Orthothecium remotifolium Ignatov & Ignatova, 2020

7. Orthothecium remotifolium Ignatov & Ignatova , sp. nova. Figs. 22A,B View Fig , 23–24 View Fig View Fig .

Type: Russia: Yakutia, Eveno-Bytantaysky District, Orulgan Range, upper course of Aenigan-Toloono Creek, 68°14’N, 128°06’E, alt. 600 m, boggy hummock on rarely flooded creek bank, 8.VIII.2011, Ignatov 11-4134 (Holotype: MHA 9029738), isotype: MW 9049153, https:// plant.depo.msu.ru/public/scan.jpg?pcode=MW9049153. Figs. 22A View Fig , 23A–J View Fig , 24A–D View Fig . [DNA sequences: nuclear ITS MT681154 View Materials , plastid trnF–trnS MT683729 View Materials ].

Diagnosis: Orthothecium remotifolium differs from O. strictum in a more broadly triangular leaf shape vs. lanceolate to ovate-lanceolate, leaf margin serrulate below mid-leaf vs. entire to serrulate only near apex, and incurved, flat or occasionally recurved vs. usually recurved, rarely almost flat leaf margins; from O. acuminatum it differs in the more gradual tapering of leaf to apex vs. leaves more abruptly contracted to apex in O. acuminatum and leaves erect to spreading vs. commonly tightly appressed.

Description: Plants small, slender, light-green or yellowish-green, glossy. Stems 1–3 cm long, loosely to densely terete-foliate, loosely fasciculate branched to almost unbranched. Leaves erect-spreading, occasionally slightly secund, 0.7–1.2× 0.3–0.4 mm, ovate-triangular, gradually tapered into short, narrow acumen, slightly narrowed at base, not decurrent, moderately concave, eplicate to weakly plicate; margins flat, incurved or in some leaves recurved in upper half, rarely recurved at larger distance, often on one side; cells 30–50×7–9 µm. Gemmae up to 100 µm long, of 5–6 cells in one row, except the top where cells occasionally are two. Sporophytes unknown.

Distribution and ecology. This species was collected in Eurasia so far in a few places: two times in Yakutia, Orulgan Range, 68°N, at 600 and 800 m alt., at and above “tree-line” (where 3 m tall Salix and Larix can grow) in that area, in wet tundra, at a brook bank; once in southern Taimyr, Anabar Plateau, 71°N, ca. 400 m, in a crevice of dolomite cliff; and also it was found in two collections from the Franz Josef Land (80°N), near a pool on terrace of N-facing slope, and inexact habitat close to shore of the Bay Tikhaya.

Additional specimens examined: EUROPEAN RUSSIA: Arkhangelsk Province: Franz Josef Land: insula Scott Keltie, 25.VII.1933, V.P. Savicz 888 (LE); Hooker Island, 1-3.VII.1929, I.M. Ivanov s.n. (LE). ASIAN RUSSIA: Krasnoyarsk Territory, Anabar Plateau, slope of height 424 to Kotuykan River valley, Fedosov 07-305 (MW9110081).

Differentiation and variation. Orthothecium remotifolium looks like a of small morph of O. strictum , differing in the long, evenly foliated shoots with distantly arranged, erect-spreading to widely spreading, quite concave leaves that are relatively broader and shorter and mostly also smaller (0.7–1.2× 0.3–0.4 mm vs. most commonly 0.8–1.8× 0.3–0.6 mm in O. strictum ). Habitually, this species is not distinct from some morphs of O. strictum , and we realised and properly evaluated the microscopic differences only after we retrieved the molecular data which showed a strong differentiation from O. strictum .

The most arguable decision was the possible identity of this species with Orthothecium acuminatum . That species was described from Greenland and Ellesmere Island in high arctic Canada, and later lectotypified with a specimen from Greenland ( Grout, 1928). In the end of detailed Latin description, Bryhn (1906) provided a short summary in Danish: “This new species that in habit mostly looks like Orthothecium strictum , differs from the latter – and all the other species of Orthothecium – by the peculiar leaf shape and toothed leaf borders” (translation by Irina Goldberg). According to the description, leaf shape is ovate-triangular, abruptly contracted to the acumen. The description also mentioned plane leaf margins.

Courtesy of Siri Rui (herbarium O), we were able to study high resolution scanned images of the type material, including the lectotype of Orthothecium acuminatum (“Bryophyta in itenere polari Norvegorum secunda collectum # 2786, Orthothecium acuminatum Bryhn sp.n., America arctica, Kong Oscars Land, Gaasefjord, Lat. sept. circiter 76°30’, Mense Junis Anni 1901, legit Herm. S. Simmons, Determ. N. Bryhn” O-B-100188).

Leaf details were not seen in these scans, however the lectotype and two syntypes studied contain plants with a julaceous foliage that is very distinct not only from the type material of O. remotifolium and other Yakutian collections, which are typically rather distantly foliate and their leaves are spreading at wide angle ( Figs. 23 View Fig , 24 View Fig ) but also from plants from more northern parts of Eurasia, Taimyr and Franz Josef Land which in different shoots vary from imbricate ( Fig. 24E View Fig ) to erect ( Fig. 24G View Fig ) and spreading foliage ( Fig. 24F, H View Fig ). Unfortunately, the fresh material from European and North American Arctic was unavailable for molecular studies, which leaves the confirmation of molecular distinctness between O. remotifolium and O. acuminatum pending to the future studies.