Pseudoleskeella rupestris var. tenuis Ignatov & Ignatova, 2022

Pseudoleskeella rupestris var. tenuis Ignatov & Ignatova , var. nov.

Type: Russia, Republic of Sakha / Yakutia , EvenoBytantaisky District , Orulgan Range , upper course of Aenigan-Toolono Creek , 68°16’, 128°25’E, 900 m alt., S-faced cliffs in narrow gorge, 6 Aug 2011 Ignatov 11- 4533 ( MHA 9060832 About MHA ). Holotype MHA, isotype MW. Figs. 2 View Fig ‘3120’, 3.

Diagnosis: Pseudoleskeella rupestris var. tenuis differs from var. rupestris in having smaller plants, usually shorter (to 0.5–0.6 vs. 0.6–0.9 the leaf length) and thinner costae in leaves from erect shoots, and short, double vs. single costae in many leaves from creeping shoots.

Description: Plants small to medium sized, pale green or yellowish-green, in loose mats. Stems creeping to ascending and erect, 1.0– 1.5 cm long, irregularly branched, terete-foliate; hyalodermis absent, central strand present. Leaves from erect shoots straight, 0.5–0.7× 0.2–0.4 mm, from ovate bases ± abruptly tapered into lanceolate, narrow, straight or slightly curved acumina; margins plane, subentire or finely serrulate above; costae single, thin, to 0.5(0.6) the leaf length or, in poorly developed plants, short and double; cells in mid-leaf rounded-polygonal or elongate-rhomboidal, 10–15×5–7 µm, with moderately thickened walls, smooth. Leaves from creeping shoots with wider bases and usually with short and double costae or with short single costae. Sporophytes unknown.

Other specimens examined: Perm Province, Bezgodov 16 Jul 2017 #194 ( MHA9049390 About MHA ) ; 28 Jul 2017 #325, #329 ( MHA9018309 About MHA , MHA9018303 About MHA ); 15 Jul 2017 #143 ( MHA 9049420 About MHA ) ; 9.VIII.2005 #106, #53 ( MHA9046519 About MHA , ( MHA9049520 About MHA ) . Altai Republic, Ignatov 32/29, 32/30, 32/31 ( MHA9046619 About MHA , MHA9046337 About MHA , MHA9046620 About MHA ). Republic of Sakha / Yakutia, Orulgan Range, Ignatov 11-4363, 11-4071 ( MHA9046637 About MHA , MHA9046634 About MHA ) .

This variety grows on rocks (limestones, aleurolites, shists), in the Urals at 180–760 m elev., in Orulgan Range, Yakutia at 670 m, in Altai at 2150–2200 m.

Differentiation: Pseudoleskeella rupestris var. tenuis

tenuis are usually narrower ovate and the acumina are longer (however, these characters occasionally overlap). In optimally developed plants of P. tectorum costae in the majority of leaves are forked or double, while in P. rupestris var. tenuis costae are single in leaves from upright shoots and forked or double in leaves from creeping shoots. Similarly, this character separates P. rupestris var. tenuis from var. rupestris , the latter variety always having leaves from all shoots with single, stronger and longer costae (cf. Fig. 2B View Fig vs. Fig. 4 View Fig ). The isotype of P. sibirica ( Fig. 4A, C–D View Fig ) has all leaves with long, single costae, thus it belongs to P. rupestris var. rupestris .

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Forked or double costae also occur P. papillosa , but this species is very different in small size of plants and prominent, massive papillae on the dorsal side of the leaves (Fig. 5).

2) Papillose laminal cells

This is another character used in keys of Pseudoleskeella , specifically for the identification of P. papillosa . This species has conspicuous papillae over most cells (Fig. 5D). Papillae are occasionally observed on leaves of P. tectorum as well, especially if the stem with undetached leaves is put in the microscope slide (Fig. 5A–C). These

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A

papillae are less numerous, and not so sharply delimited, as their ‘slopes’ are more gentle.

3) Brood branches

Most moss floras key out P. nervosa as the only species characterized by the presence of fragile branches with minute leaves clustered in leaf axils near shoot tips. However, we found similar brood branches in many collections of P. papillosa from Russia ( Fig. 6 View Fig ). Unlike P. nervosa , they are less tightly crowded, thus looking less ‘stellate’. Anyway, in some cases strict following of a key may result in erroneous identifications.

4) Bistratose leaf margins

Leaf margins are commonly unistratose in most species of Pseudoleskeella . However, in the Caucasus and Crimea there are plants with partly bistratose leaf margins which were described as Leskeella incrassata (Lindb. ex Broth.) Broth. This species is indistinguishable from P. nervosa in all other characters. Similar plants also occur sporadically in southern Europe. Molecular-phylogenetic data do not support the taxonomic recognition of L. incrassata (specimens from the Caucasus, OK3143– 3146 have bistratose margins, while specimens from Sakhalin and from Nizhhy Novgorod are unistratose).

5) Thick-walled cells

This character is somewhat difficult to demonstrate and apply. Pseudoleskeella catenulata is usually keyed out as a species with thickest cell walls within the genus; it also has short leaf acumina, often with subobtuse apices, but morphotypes with slightly longer acumina and acute apices are not rare. These latter plants can be confused with short-leaved plants of extremely variable P. rupestris (compare Fig. 7S and Fig. 4C, F View Fig ). However, P. catenulata always has leaves with costae to 0.5–0.6 the leaf length, while in P. rupestris costae extend far above mid-leaf, becoming weakly delimited from adjacent cells in the leaf acumina. Cell wall thickness is also helpful, as leaf cells of P. rupestris are usually much thinner-walled (cf. Fig. 4D View Fig vs. Fig. 9 View Fig A’). If it is difficult to estimate if cells are thick- or thin-walled, another distinguishing character can be used: the leaf cell areolation of P. catenulata is not contrasting between juxtacostal and marginal areas ( Fig. 8A View Fig ), whereas in P. rupestris rhomboidal and elliptical, thinner-walled cells in mid-leaf differ contrastingly from several rows of quadrate to transversely rectangular, thicker-walled marginal cells ( Fig. 8B–C View Fig ).

The clade of P. catenulata in the molecular phylogenetic tree is well supported ( Fig. 1 View Fig ), but it includes one specimen from Sakhalin Island differing from other specimens of this clade in morphology. It has very long acuminate leaves and only moderately thickened cell walls, in contrast to leaves with short acumina and thick-walled cells of P. catenulata . DNA was extracted twice from this specimen in order to exclude possible errors; two identical sequences were obtained. This plant is described below as a new species.