Tortella splendida Köckinger & Hedenäs, Lindbergia 2023

Tortella splendida Köckinger & Hedenäs, Lindbergia 2023 View in CoL (e24903): 20, 8G–J, 11. 2023. Fig. 2 View Fig , 6B, G View Fig .

Plants medium-sized to large, on loose or dense cushions, light green, yellowish-green or rusty-brownish. Stems to 6 cm long, irregularly branched, densely foliose, weakly tomentose, round in transverse section, without central strand. Leaves 3.0–4.5(–7).0× 0.6–1.2 mm, lanceolate or linear-lanceolate, with length:width ratio 5–7:1, lower leaves erect-spreading when dry, upper leaves incurved and slightly twisted; erect-spreading to widely spreading when wet, straight from above view, limbs gradually narrowed upwards, narrowly acuminate at apex, not cucullate, canaliculate distally; leaf bases short or elongate-rectangular, not or slightly widened, without distinct shoulders; leaf margins plane or widely incurved distally, entire, not undulate; costa strong, (75–) 100–150(–200) µm wide at leaf base, gradually tapering distally, excurrent into short, weakly denticulate mucro, with quadrate, papillose cells on ventral surface from above base, with elongate, smooth cells on dorsal surface or with few spinulae, in transverse section with 1(2) layers of guide cells, 2 stereid bands, differentiated ventral epidermis and weakly differentiated dorsal epidermis; lamina unistratose, rarely with few bistratose spots; upper and median laminal cells rounded-quadrate, 7– 11 (–13) µm wide, thick-walled, densely papillose, papillae low, obscuring cell walls; basal laminal cells oblong-rectangular, thick- or moderately thin-walled, smooth, yellowish, basal marginal cells often narrower than central and juxtacostal cells; boundary between basal and limb cells usually gradual, U-shaped, rarer abrupt, V-shaped. Dioicous, sporophytes unknown.

Distribution and ecology. Tortella splendida is an arcto-alpine species, occuring in Asian and North American Arctic regions, in the mountains of Central Europe ( Köckinger & Hedenäs, 2023), Caucasus ( Kuznetsova et al., 2023), southern Siberia, Russian Far East (our data), China ( Eckel, 2007), and in North America in Colorado and Maine ( Eckel, 2007). It is common in northern Taimyr and Chukotka, especially on Vrangel Island. It grows on gravelly soil, in niches between rocks of rockfields, rock crevices, on rocks outcrops, especially in areas with calcareous bedrocks; it also occurs along brooks and in polygonal and spotty tundra, where it forms large pure fufts or grows among other mosses.

Differentiation. Tortella splendida is similar to T. tortuosa in having leaves with costa papillose on ventral surface and stems lacking central strand. However, its leaves are straight when wet (usually sigmoid and often secund in T. tortuosa ); their limbs are gradually narrowing from above base (limbs have parallel margins for a long distance in T. tortuosa ); leaf margins are not wavy (usually strongly wavy in T. tortuosa ); transition between basal and limb cells is gradual (mostly abrupt, V-shaped in T. tortuosa ), elongate basal cells do not extending high along leaf margins (reach far up in T. tortuosa ); it also has less tomentose stems (often densely tomentose in T. tortuosa ). Basal cells are usually yellowish in arctic plants of T. splendida , contrary to white basal cells of T. tortuosa . Unlike T. splendida , T. tortuosa never possess two layers of guide cells in costa. There is some similarity in leaf shape between T. splendida and T. cuspidatissima , but the latter species can be readily separated by having leaf costae smooth ventrally and stems with weak central strand. Also in T. s plendida on average cells in the upper part of the leaf are smaller (7–11 µm vs 11–16 µm in T. cuspidatissima ) and costa is wider (100–150(–200) µm vs 50–100 (120) µm in T. cuspidatissima ).