Isopterygiopsis muelleriana (Schimp.) Z. Iwats., J. Hattori Bot. Lab.

Isopterygiopsis muelleriana (Schimp.) Z. Iwats., J. Hattori Bot. Lab. View in CoL 33: 379. 1970.

— Plagiothecium muellerianum Schimp., Syn. Musc. Eur. View in CoL 584. 1860. — Isopterygium muellerianum (Schimp.) A. Jaeger, Ber. Thätigk. St. Gallischen Naturwiss. Ges. 1876 –77: 441. (Gen. Sp. Musc. 2: 1259). 1878. Figs. 4 View Fig , 5 View Fig , 7A–B, D, F, I, L, M View Fig .

Stems to 2 cm long, central strand consisting of few cells present, rarer lacking. Leaves erect-spreading to spreading, loosely or densely arranged, (0.5–)1.0–1.5 ×(0.2–) 0.3–0.4 mm, ovate-lanceolate, gradually attenuate, with 1–2-seriate apical portion 2–4 cells long, moderately concave, not cucullate; margins flat, entire; laminal cells 60–100(–120)×4–5 µm, alar cells not differentiated. Specialized asexual reproduction by axillary propagulae of 3–4 cells in one row. Sporophytes rare, unknown in Russia. [Perichaetial leaves gradually narrowed into narrow acumen with serrulate margins. Setae 1.2–1.5 cm. Capsules ca. 1.2 mm long, erect, straight to weakly curved. Spores 10–14 µm].

Distribution and ecology. Isopterygiopsis muelleriana is a mountainous species occurring in South and Central Europe and extending northward to the southern areas of Norway ( Hodgetts & Lockhart, 2020); it was also reported from Turkey ( Ros et al., 2013), Africa ( Kenya, Tanzania, Uganda) (O’Shea, 2006) and India ( Gangulee, 1978 -1980). Isopterygium sericifolium Dixon described from Kenya was synonymised with Isopterygiopsis muelleriana by Hedenäs (2001); specimen in BM (000674451) is habitually similar to European plants, as well as the drawing of leaf and shoot (https:// data.nhm.ac.uk/dataset/56e711e6-c847-4f99-915a- 6894bb5c5dea/resource/05ff2255-c38a-40c9-b657- 4ccb55ab2feb/record/4522883). Illustration in Gangulee (1978 -1980) (Fig. 1014) also shows a plant similar to European specimens rather than North Asian ones.

Both I. muelleriana and I. catagonioides occur in China. The latter species was decribed from Shaanxi Province; illustrations in “Moss Flora of China ” ( Zhang & He, 2005) also show a stem transverse section without central strand and ovate leaves abruptly narrowed into short filiform apiculus. At the same time, molecular data confirm the presence of I. muelleriana in China (Yunnan) ( Figs. 1 View Fig & 2 View Fig ).

Isopterygiopsis muelleriana View in CoL is also considered to be widespread in eastern North America. However, its distribution in these areas needs confirmation because I. catagonioides was included into it. Illustrations in Flora of North America ( Ireland Jr., 2014) likely represent I. catagonioides rather than I. muelleriana View in CoL . Photograph of stem transverse section that lack central strand and has the whole cortex of rather few cells is provided by Faubert (2014), and illustrations in “Flora of Maine” by Allen (2014) also show plants which are much more similar to O. catagonioides than to I. muelleriana View in CoL s.str. The only trn L-F sequence of I. muelleriana View in CoL from North America in Genbank is also resolved within the clade of O. catagonioides ( Fig. 2 View Fig ), as well as nad 5 region ( AY908764 View Materials ), cf. Fig. 3 View Fig .

In European Russia I. muelleriana View in CoL is known only in the Caucasus where it was collected in Dagestan and Karachayevo-Circassian Republics; collections from Dagestan represent strongly depressed plants with small leaves ( Fig. 4 View Fig : 11-12, 7A). These specimens were collected at altitudes 1900–2100 m on open slopes, on soil among grasses and rock outcrops. Plants from Karachayevo-Circassian Republic are better developed, similar to the specimen from Germany. Label data do not provide exact ecological information except for growing on soil. A single collection of I. muelleriana View in CoL from Asian Russia was made in a valley of Bureya River, within forest zone, at 370 m elevation. It grew in a flood valley, on soil bank in forest, forming thin, lax patch and being represented mainly by tiny, depressed plants with small, distantly arranged leaves and attenuate stem and branch apices.

Additional specimens examined: EUROPE: GERMANY, Tegernsee , 6. I .1919, Herzog, Paul & Schellenberg s.n. ( MW9045910 ). RUSSIA: Karachayevo-Circassian Republic: gorge of Daut River, 5.VIII.1999, Ukrainskaya 13913 ( LE). Dagestan: Charoda Distr. , Gunukh, Ignatov & Abakarova 11- 206 & 11-218 ( MHA 9038321 About MHA & 9038319) .

Differentiation. Isopterygiopsis muelleriana has ovate-lanceolate leaves more or less gradually tapered and ending with narrow, filiform apiculus. In leaf shape it is similar to Isopterygiella pulchella . However, Isopterygiopsis muelleriana has well-developed stem hyalodermis and complanate foliage, while hyalodermis in stems of Isopterygiella pulchella is absent or scarcely recognized, its stems are terete-foliate or leaves are secund. The distinctions from I. catagonioides are discussed under that species. Isopterygiella alpicola is another plant with well-developed stem hyalodermis and gradually acuminate leaves; it differs from Isopterygiopsis muelleriana in smaller size of plants, with leaves 0.3–0.8× 0.1– 0.3 mm vs. 1.0–1.5× 0.3–0.5 mm; terete foliate stems, often falcate-secund leaves; serrulate vs. entire leaf margins; and shorter laminal cells, 30–60×5–9 µm vs. 60– 100(–120)×4–5 µm.