Didymodon abramovae Ignatova & Fedosov, 2024

Ignatova, E. A., Fedosov, V. E., Kuznetsova, O. I., Fedorova, A. V. & Ignatov, M. S., 2024, On the genus Didymodon s. str. (Pottiaceae, Bryophyta) in Russia, Arctoa 33 (2), pp. 129-155 : 144

4. Didymodon abramovae Ignatova & Fedosov , species nova. Figs. 9–10 .

Type: Russia, Caucasus, Republic of Dagestan, Gunib District , 42°25’N, 46°54’E, 1850 m alt., near research station of Mountain Botanical Garden , northern macroslope of Mayak Mt. , exposed N-faced rock outcrops, 20. V .2009, Ignatov & Ignatova 09-607 (Holotype MHA9101354 , isotype MW9035943 ) .

Etymology. The species in named in honor of Anastasia Lavrentievna Abramova (1915–2012), russian bryologist, who greatly contributed to the knowledge on moss flora of Russia, in particular of the Caucasus and Russian Arctic.

Plants medium-sized, in loose or dense tufts, green, yellowish-green or brownish, dull. Stems 1–1.5 cm long, simple or branched, without hyalodermis, with central strand. Rhizoidal tubers absent. Leaves erect, appressed when dry, patent to spreading when wet, ovate-triangular, with scarcely differentiated bases, gradually narrowed into subulate acumina, with fragile apices, 1.5–2.1× 0.35– 0.5 mm, canaliculate distally; margins narrowly recurved in proximal 1/3–3/4, unistratose, entire; costa 45–60 µm wide at leaf base, slightly narrowing upwards, excurrent into long chlorophyllose awn, prominent dorsally, flat distally, on both surfaces with quadrate cells, smooth, without band of translucent cells on ventral side below apex, in transverse section semicircular, with 3–6 guide cells in 1 layer, ventral stereids in 0(1) layer, ventral epidermis differentiated, with not bulging outer walls, dorsal stereids in 1–2 layers, dorsal epidermis differentiat- ed; lamina unistratose; upper and median laminal cells rounded-quadrate, irregularly polygonal, elliptic and transversely elliptic, 6–13×4–11 µm, with moderately thickened walls, collenchymatose, smooth; basal juxtacostal cells rectangular, 20–40×7–11(–13) µm, or short rectangular to quadrate, 7–18×9–11 µm, smooth, with moderately thickened, straight walls; basal marginal cells in several rows oblate, collenchymatose. KOH-reaction yellowish-green. Specialized asexual reproduction absent. Gametangia and sporophytes unknown.

Didymodon abramovae is currently known from the Caucasus, Tyva and Yakutia. We also tentatively refer to it three other specimens, including one from Perm Territory. Its leaves with long excurrent costa make it similar to D. icmadophilus , but the latter species has leaves with wider bases, abruptly narrowed into acumina, and laminal cells papillose on dorsal surface. Long excurrent costa and fragile leaf apices are also characteristic for D. daqingii , but it can be distinguished from D. abramovae by bistratose leaf margins and costa with 2–3 layers of guide cells and no ventral stereids. Didymodon validus differs from D. abramovae by shorter excurrent costae, not fragile leaf apices, and leaves flexuose and incurved when dry (straight and appressed in D. abramovae ).

Figures

Fig. 9. Didymodon abramovae (from holotype). A: habit, dry; B: habit, wet; C, F–G, J–M: leaves; D: mid-leaf cells; E: stem transverse section; H: basal leaf cells; I: upper leaf cells; N–O: leaf transverse sections. Scale bars: 2 mm for A–B; 1 mm for C, F– G, J–M; 100 µm for D–E, H–I, N–O.

Fig. 10. Didymodon cf. abramovae (from Russia, Republic of Tyva, Kara-Khol Lake, Pisarenko 23/3, NSK, MHA9131862, isolate OK4112). A: habit, dry; B: habit, wet; C–E, G, J: leaves; F: mid-leaf cells; H: basal leaf cells; I: upper leaf cells; K–L: leaf transverse sections. Scale bars: 2 mm for A–B; 1 mm for C–E, G, J; 100 µm for F, H–I, K–L.