Didymodon cherdantsevae 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 : 145-147

5. Didymodon cherdantsevae Ignatova & Fedosov , species nova. Fig. 11 .

Type: Asian Russia, Primorsky Territory , Russky Island , vicinity of Melkovodnaya Bay , gentle forested slope of Russkaya Creek valley , 43.0021°N, 131.80941°E, 23 m alt., oak dominated forest with rock outcrops, roadside, 14.IX.2024 Fedosov 24-351 (Holotype MW9092502 , isotype MHA) .

Etymology. The species in named in honor of Valentina Yakovlevna Cherdantseva (1939–2013), russian bryologist, who greatly contributed to the knowledge of moss flora of the southern Russian Far East.

Plants medium-sized, in loose tufts, green or yellowish-green, dull. Stems ca. 1 cm long, simple or branched, without hyalodermis, with central strand. Rhizoidal tubers absent. Leaves slightly flexuose and incurved when dry, widely spreading when wet, forming an angle ca. 90° with stem, occasionally with reflexed apices, S-shaped in side view, from short rectangular bases gradually narrowed into long, narrow triangular acumina, exceeding bases 1.5–2 times in length, acuminate, not decurrent, 1.7–1.9× 0.3–0.35 mm, canaliculate distally; margins narrowly recurved in proximal 1/3–3/4, unistratose, entire; costa 40–50 µm wide at leaf base, slightly narrowing upwards, excurrent into short mucro, prominent dorsally, flat ventrally, 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 1(2) layers, ventral epidermis differentiated, with weakly bulging outer walls, dorsal stereids in 2–4 layers, dorsal epidermis differentiated; lamina unistratose; upper and median laminal cells rounded-quadrate, elliptic and transversely elliptic, 8–11×8–10 µm, with moderately thickened walls, weakly papillose on both surfaces; basal juxtacostal cells short rectangular, 13–25×7–9 µm, smooth, with moderately thickened, straight walls; basal marginal cells in several rows shorter, short rectangular and quadrate. KOH-reaction yellow. Specialized asexual reproduction absent. Dioicous. Perigonia lateral. Setae ca. 2 cm long, reddish-brown. Capsules cylindrical, 1.5 mm long, straight, light brown. Annuli not seen. Opercula high conic, straight, ca. 1 mm long. Peristome with very low basal membrane, teeth 32, 750–770 µm long, spirally twisted when dry, densely papillose. Spores 9–11 µm. Calyptrae not seen.

Didymodon cherdantsevae is currently known only from Primorsky Territory, on Russky Island and in Dalnegorsk District, near Sedaya Mt. In both localities it was collected at roadsides, on a rubble scree and rocky soil. Another species having leaves with comparatively short bases, long acumina, and weakly papillose laminal cells is D. hengduanensis ; it was described from China and revealed in Russia in the present study. It differs from D. cherdantsevae by sligtly larger leaves with wider bases, 1.8–2.7× 0.6–0.9 mm vs 1.7–1.9× 0.3–0.35 mm, erectopatent to patent when moist (spreading at 90° with stem in D. cherdantsevae ), and less strong stereid bands in transverse sections of costa.

Figures

Fig. 11. Didymodon cherdantsevae (from holotype). A: habit, dry; B: habit, wet; C: cap- sule; D: stem transverse section; E, K: upper laminal cells; F–I: leaves; J: mid-leaf cells; L– N: leaf transverse sections; O: basal leaf cells. Scale bars: 1 cm for A; 2 mm for B–C; 1 mm for F–I; 100 µm for D–E, J–O.