Tortella spitsbergensis (Bizot & Thér.) O. Werner, Köckinger & Ros

Tortella spitsbergensis (Bizot & Thér.) O. Werner, Köckinger & Ros View in CoL , Nova Hedwigia 98(3–4): 287. 2014. — Grimmia spitsbergensis Bizot & Thér., Bull. Sci. Bourgogne 5: 70. 71. 1935. Fig. 3 View Fig , 6D, I View Fig .

Plants medium-sized to large, in dense tufts, yellowish-green or brownish, dull. Stems to 6 cm long, irregularly branched, densely or sparsely foliate, more or less tomentose, triangular or round in transverse section, with large, sharply delimited central strand, consisting of small, thinner-walled cells. Leaves (2.0–)2.5–3.5(–4.0) × 0.4–0.7 mm, with ovate bases and lanceolate limbs, contorted and twisted when dry, erect-spreading, often with recurved acumina when wet, sigmoid, gradually tapered distally, narrowly acuminate, not cucullate at apex; widely keeled in midleaf; leaf bases wide-elliptic, well differentiated, wider than limb, with or without distinct shoulders; margins plane in mid-leaf and widely incurved above, entire, slightly wavy; costa strong, 50–75(–110) µm wide at leaf base, gradually tapering upwards, on ventral and dorsal surfaces with elongate, smooth cells, excurrent into long, smooth mucro, in transverse section with 1 layer of guide cells, two stereid bands, ventral epidermis not or weakly differentiated, dorsal epidermis differentiated; lamina unistratose; upper and median laminal cells rounded-quadrate and transverse elliptical, 8– 11(–13) µm wide, thick-walled, densely papillose, papillae low, not obscuring cells walls; laminal cells in central and juxtacostal part of leaf base elongate-rectangular, thick-walled, smooth, yellowish, basal marginal cells considerably shorter and wider in the widest part of leaf base, forming pellucid area; transition from smooth basal cells and papillose limb cells gradual, border W-shaped, smooth cells reach into limb higher near costa than at leaf margins. Dioicous, sporophytes unknown.

Distribution and ecology. This species was described from Spitzbergen ( Norway). In Russian handbooks and check-lists it was provided under the name Trichostomum cuspidatissimum (Savicz-Lyubitskaya & Smirnova, 1970; Ignatov et al., 2006). Werner et al. (2014) also confirmed the presence of Tortella spitzbergensis Canada (Newfoundland) and in Russia (Arctic Siberia and Chukotka). In the course of our study, we found it to occur on Novaya Zemlya and being common on Northern Taimyr and Chukotka. Outside Arctic, it is known in Russia in Anabar Plateau, Yakutia, Magadan Province, Kamchatka, Khabarovsk and Zabaikalsky Territories, Buryatia and Tyva. It grows in wet arctic and mountain tundra, boggy sites, on rocky slopes, screes, wet rock outcrops, often on calcareous rocks.

Differentiation. Tortella spitzbergensis differs from all other species of the genus in having large, sharply delimited stem central strand; it is formed of very thin-walled, numerous small cells surrounded by firm-walled cells of central cylinder. Presence of stem central strand, costa smooth on ventral surface, leaves with wide-ovate bases and comparatively short, lanceolate acumina differentiate T. spitzbergensis from T. splendida . Tortella cuspidatissima possesses stem central strand, but the small one; it also has gradual transition between basal and limb cells, but its juxtacostal basal cells reach into the limb at the same height as the marginal ones; its basal marginal cells are only slightly wider than central cells, of the same width or narrower.