Lazarenkoa microphylla Ignatov & Ignatova, 2019

Lazarenkoa microphylla Ignatov & Ignatova , sp. nova Figs. 4–5

Etymology: species epithet means small leaves.

Type: Primorsky Territory, Partizansk District , Nakhodka City surroundings, foothills of the Lozovyj Range (former Chandolaz), E-facing slope, or rocks in streamlet bed. 43°00’51.1”N, 133°01’13.6”E, 240 m alt. 21.09.2015, Coll. O GoogleMaps . D. Tumurova VL-1-14 (holotype MHA; isotype: UUH) .

Description: Plants tiny, dark green, dull, in prostrate tufts. Stems creeping, up to 7 mm long, irregularly or subpinnately branched; branches to 2 mm long, patent upward; paraphyllia absent. Stem leaves appressed when dry, erectopatent when moist, ovate-lanceolate to triangular, 0.25–0.35× 0.1–0.15 mm, plane; branch leaves shorter and relatively broader, ovate-triangular, 0.10– 0.20× 0.05–0.10 mm, (the smaller leaves of 100×50 µm being 18 cells along the margin and 9 cells wide); costa 20–50 µm wide at base, occupying 1/3–1/6 the leaf base, ending shortly below the apex; margins entire to slightly and irregularly crenulate at places; leaf cells throughout the lamina isodiametric to oblate, 5–8 µm, thick-walled, with low bulgings on dorsal surface, so leaf dorsal side at lateral view looks rough. Dioicous? Inner perichaetial leaves triangular, 0.5× 0.25 mm, narrowly acute, costa strong, gradually narrowing upwards, ending below apex. Perigonial leaves ovate, 0.3× 0.2 mm, blunt to rounded at apex, inner perigonial leaves ecostate. Sporophytes not seen.

Comments on descriptions: The dioicous sexual condition is identified with question mark: all shoots we examined had only one sex (most had no gametangia), however, the plant is copiously branched and so fragile that we admit that the studied male and female shoots grew from the same mother-plants, and we simply failed to find such juntction in the limited material available for study.

Differentiation. Lazarenkoa microphylla is similar to Leskea scabrinervis , which diagnostic characters are also formulated as plants with very small leaves and costa rough at back ( Tong et al., 2002). However, leaf size in the latter species is reported as 0.4–1.0 mm long ( Tong et al., 2002), whereas in Lazarenkoa the longest leaf we found was 0.35 mm long, and many leaves were between 0.10 and 0.15 mm. The difference between the two is also in different nuclear ITS sequences. The latter species is autoicous, although this character of sexual condition is not reliable in this case (see comment on description). Also, according to Tong et al. (2002), Leskea scabrinervis grows on trees, while Lazarenkoa was collected on rocks in temporary stream bed. This type of habitat calls for comparison with North American Platylomella lescurii , which was found to be related to Leskea scabrinervis by Qi-Ying et al. (2019) in molecular phylogenetic analysis. Platylomella is only slightly larger than Leskea scabrinervis , but it has bistratose leaf margins, very different lamina areoaltion of cells with angulate lumina, curved capsule, and apparent autoicous sexual condition ( Christy, 2014).

In any case, neither Lazarankoa, nor Leskea scabrivervis do not belong to the genus Leskea , which is well delimited in molecular phylogenetic tree ( Figs. 2–1), and has clearly papillose laminal cells.