Pseudoleskeella sachalinensis Ignatov & Ignatova, 2022

Pseudoleskeella sachalinensis Ignatov & Ignatova , spec. nov.

Type: Russia, Sakhalinskaya Province, Sakhalin Island , Smirnykh District , Nature Reserve “Vaida Mountain”, 49°52'N, 143°28'E, 450 m alt., on rocks in fir forest, 21 Aug 2006 Ignatov & Teleganova 06-323 ( MHA9046548 About MHA ). Holotype MHA, isotype MW. GoogleMaps

Diagnosis: Pseudoleskeella sachalinensis is similar to P. rupestris var. rupestris in having leaves with long acumina, long single costae, and elongate-rhomboidal leaf cells, but differs in having leaves from erect stems with even longer acumina, constituting ca. 0.5–0.7 the leaf length (0.3–0.5 the leaf length in P. rupestris var. rupestris ) and longer cells in distalmost leaf portion: 4–6:1 vs. 2–4:1.

Description: Plants medium-sized, green or yellowish-green, in loose mats. Stems creeping and ascending to erect, 1.0– 1.5 cm long, hyalodermis absent, central strand present. Leaves from erect shoots straight or slightly falcate-secund, 0.7–1.0× 0.2–0.4 mm, from an ovate base ± abruptly tapered into long, narrow lanceolate, straight or slightly curved acumina constituting ca. 0.5– 0.7 the leaf length; margins plane, entire or serrulate in places; costae single, thin, to 0.6–0.8 the leaf length; cells in mid-leaf elongate-rhomboidal, 19–35×6–8 µm, towards margins shorter, rhomboidal, quadrate and transversely rectangular, firm-walled, smooth; upper cells of leaf acumina oblong, 16–35 µm long, 4–6:1. Leaves from creeping shoots slightly smaller, with wider bases, costa single. Sporophytes unknown.

Pseudoleskeella sachalinensis is currently known only from the type locality.

Differentiation: Pseudoleskeella sachalinensis differs from all other species of the genus by the longest – ca. 0.5–0.7 the leaf length – leaf acumina, and especially long – 4–6:1 – cells in the uppermost leaf portion. Leaf acumina of P. rupestris are usually shorter, composed of shorter cells. However, in some morphotypes of P. rupestris leaf acumina in proportion to leaf length approach those of P. sachalinense and are similarly narrow acuminate (Fig. 7G). In this case, the difference in cell length and width of acumina are important distinguishing characters: a number of long cells in leaf acumina is larger in P. sachalinensis and the acumina are 2–4 cells wide for a longer distance than in P. rupestris (cf. Fig. 7C–E vs. F).