Arvernella pisarenkoi Ignatov & Ignatova

Arvernella pisarenkoi Ignatov & Ignatova

Type: Russia, Sakhalin Island , Tymovo Distr. , Nabilsky Mt. Range , Chamginsky pass, creek – a tributary of Skalistaya River, 54°44’N, 143°16’E, 707 m alt. On limestone outcrops. 12 Sep 2009, coll. Pisarenko O.Yu. op03738 (holotype MHA!, isotypes NSK!, MW!). GoogleMaps

Etymology: the species is described in honor of Olga Yu. Pisarenko, bryologist from the Central Siberian Botanical Garden (Novosibirsk), who studied the moss flora of Asian Russia and collected the type specimen of the described species.

Diagnosis: Arvernella pisarenkoi is similar to A. microclada in very small plant size, similar shape of leaves, and spore size, but differs in inclined to pendent capsules; slightly larger leaves, 0.27–0.40× 0.10–0.16 mm vs. 0.14– 0.35× 0.055–0.08 mm in A. microclada ; shorter laminal cells, 9–15(–20)×5–6(–7) µm vs. 17–22×3–10 µm, a more distinct costa, which is absent or very short and indistinct in A. microclada ; perichaetial leaves of A. pisarenkoi are also larger, 0.9–1.15 mm vs. 0.3–0.4 mm long.

Description. Plants minute, in moderately dense, tiny, delicate mats, green to dark green. Stems creeping, to 10 mm long, stem composed of homogeneous cells, without

central strand, epidermal cells with only slightly thicker walls than cells inwards, terete foliate, irregularly branched, branches diverging at about right angle, 2–4 mm long, terete foliate; rhizoids inserted below leaf insertion; axillary hairs 4–5-celled, upper cell ca. 20×10 µm; paraphyllia absent; proximal branch leaves linear to lanceolate. Stem leaves appressed when dry, erect when moist, 0.27–0.40× 0.10–0.16 mm, triangular-lanceolate, gradually narrowed to apex, not or very slightly narrowed to base, not or very shortly decurrent; costa forked, to 0.2–0.4 the leaf length, indistinctly delimited; margins plane, obtusely serrulate throughout; laminal cells 9–15 (–20)×5–6(–7) µm, with length to width ratio 2.0–2.5 (–3.4):1, moderately thick-walled, smooth or weakly prorate; alar cells sub-quadrate to short-rectangular, 7–8 µm wide, forming indistinctly delimited group 5–7 cells long and 2–3 cells wide. Branch leaves somewhat smaller and narrower than stem leaves. Autoicous. Perigonia budlike, perigonial leaves ovate, strongly concave. Perichaetial leaves straight, 0.9–1.15× 0.4–0.5 mm, triangular-lanceolate, acuminate, eplicate, with thick, gradually tapered, indistinctly delimited costa to 0.6 the leaf length. Setae to 9 mm, erect to somewhat flexuose, smooth, brownish to reddish-brown. Capsules inclined to somewhat pendent, urn 0.5–0.7× 0.2–0.3 mm, elongate-ovoid, strongly contracted below mouth when dry and empty. Annuli deciduous. Opercula conic and shortly and broadly rostrate. Exostome teeth 260–300 µm long, cross-striolate below, papillose above; endostome with basal membrane ca. 1/2 of its length, segments narrow, about as long as exostome teeth, cilia 1–2, slightly shorter than segments, nodose. Spores 10–13 µm.

A C B

Differentiation. Sterile plants of A. pisarenkoi could be confused with Serpoleskea confervoides , but they are smaller, with appressed leaves when dry, and also (1) the perichaetial leaves of A. pisarenkoi have a costa that is absent in Serpoleskea ; (2) the stem is formed by homogeneous cells, whereas in Serpoleskea cells of two outer stem layers are markedly smaller than the inner cells.

Using the keys in Kanda (1975) and Noguchi et al. (1991), Sakhalin plants were previously identified as Platydictya fauriei Card. (the genus Platydictya was accepted in that treatment in its old sense, being almost equal to Amblystegiella ) and published by Chedrantseva et al. (2018). However, Platydictya fauriei has linear-rhomboid cells 20–25×3.5–5 µm vs. 9–15(–20)×5–6(–7) µm in A. pisarenkoi ; upper leaf cells even longer, 20–28 µm vs. not longer than mid-leaf cells; laminal cells smooth vs. somewhat prorate; alar cells somewhat enlarged and hyaline vs. not enlarged; perichaetial leaves oblong-lanceolate, 1.0× 0.3 mm, plicate, without prominent costa vs. ovate, 0.90–1.15× 0.4–0.5 mm, eplicate, with prominent costa; spores 12–15 vs. 10–13 µm.

Ecology. According to Pisarenko field notes (letter of 4 June 2021), the collection was done on a small outcrop (not shown, more exact loc. data from map 50.73356°N, 143.26138°E) on a slope to small stream valley in the mixed forest ( Fig. 4B,C View Fig ). The forest with tall trees of Picea yezoensis and Abies sachalinensis grow in this area only in sheltered valleys, while more exposed slopes are covered by Betula ermanii s.l. and Alnus fruticosa crooked forest ( Fig. 4A View Fig ) and Pinus pumila tickets (shrubby pine, Fig. 4A, C View Fig ). Forest is usually intermingled with tall-herb communities with Filipendula kamchatica , species of Cacalia , Angelica , and Senecio ).

Collection from that outcrops and nearby (including stream, forest floor and more exposed rocks) include: Amphidium lapponicum, Bartramiopsis lescurii, Brachythecium baicalense , B. cirrosum , Codriophorus corrugatus, Cyrtomnium hymenophylloides, Dilutineuron brevisetum, Eurhynchiastrum pulchellum , Fissidens dubius, Gymnostomum aeruginosum, Homalia trichomanoides, Hygrohypnella ochracea, Isopterygiella pulchella , Lescuraea incurvata , L. patens , L. radicosa , L. saxicola , Mnium thomsonii, Myurella julacea, Niphotrichum canescens , Platyhypnum cochlearifolium , P. duriusculum , Oxystegus tenuirostris , Plagiomnium medium , Plagiothecium cavifolium , P. denticulatum , P. nemorale, Pleurozium schreberi, Pogonatum contortum, Pohlia cruda, Rhynchostegium aquaticum , Saelania glaucescens , Schistidium lancifolium , S. rivulare , and Sciuro-hypnum plumosum.

The environments of the Sakhalin locality are in many aspects similar to those of Arvernella microcalda habitats in France (Hugonnot, pers. comm.), where it grows also at the elevation at about timberline, at transition of Fagus forest to tall-herb meadows with Cacalia, Cicerbita, Rumex , etc. Associated moss species include, among others, Oxystegus tenuirostris and Lescuraea patens , the latter being quite rare in Russia ( Hugonnot & Hedenäs, 2015).