Didymodon nigrescens (Mitt.) K. Saito, J. Hattori Bot. Lab.

Afonina, M. A., Kuznetsova, O. I. & Ignatova, E. A., 2022, A revision of the Didymodon perobtusus group (Pottiaceae, Bryophyta) in Russia, Arctoa 31 (2), pp. 191-204 : 203

Didymodon nigrescens (Mitt.) K. Saito, J. Hattori Bot. Lab. 39: 510. 1975. — Barbula nigrescens Mitt., J. Proc. Linn. Soc., Bot., Suppl. 1: 36. 1859. Figs. 8-9

Plants rigid, in dense tufts, dark brown, occasionally green at tips, dull. Stems 10–25 mm, repeatedly branched; hyalodermis absent, cortical cells in 1–2 rows, medullar cells in 3–4 rows, thick-walled, central strand absent. Leaves appressed when dry, erect when moist, in lower and middle parts of stems 0.5–0.7× 0.3–0.4 mm, upper leaves to 1.0× 0.4 mm, from ovate bases + abruptly narrowed into triangular acumina, subobtuse at apex, concave, not keeled distally; margins narrowly recurved from base to midleaf; costa moderately thick, ca. 40 µm wide at base, not or slightly narrowed distally, subpercurrent, semicircular in transverse section, with two guide cells, dorsal and ventral epidermis, dorsal stereid band absent or 1-layered in lowermost portion of costa; cells thick-walled, upper and middle laminal cells 8–11×8–15 µm, papillose, papillae low, branched, 1–2 per cell; basal juxtacostal cells ovate, 10–25×8–11 µm, smooth, in upper leaves in oblique rows, basal marginal cells shorter, ovate to transversely ovate. Specialized vegetative reproduction absent. Dioicous, only plants with archegonia were seen. Sporophytes unknown in Russia.

Ecology. The species was collected on one locality on Sakhalin Island, at the top of low calcareous ridge, in crevices and on surfaces of dry cliffs.

Specimens examined: RUSSIA: Sakhalinskaya Province, Sakhalin Island, Smirnykh Distr. , Nature Reserve “Vaida Mountain”, 900 m alt., Ignatov & Teleganova 06-3543, MW9036033 ; same place, 920 m alt., Ignatov & Teleganova 06-3544, MW9036034 .

Figures

Fig. 8. Didymodon subandreaeoides (from: Russia, Yakutia, Sette Daban Range, Ivanov 17-605, MHA9027661). A: habit, dry; B–C: leaf transverse sections; D: gemmae; E: upper leaf cells; F, K: lower stem leaves; G: leaf from innovation; H: stem transverse section; I: mid-leaf cells; J: perichaetial leaf; L: subperiachaetial leaf; M: basal leaf cells. Scale bars: 2 mm for A; 0.5 mm for F– G, J–L; 100 µm for B–E, H–I, M.

Fig. 9. Didymodon nigrescens (from: Russia, Sakhalin Island, Ignatov & Teleganova 06-3543, MW9036033). A: habit, dry; B: habit, wet; C–D: upper leaf cells; E–H, J–K: stem leaves; F: mid-leaf cells; G: stem transverse section; I: basal leaf cells; L–O: leaf transverse sections. Scale bars: 2 mm for H; 0.5 mm for C–D, F–G, J–K; 100 µm for A–B, E, I, L.