Didymodon mongolicus

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 : 135

Didymodon mongolicus

This species was described in 2016 from Northern China and Mongolia ( Zhao et al., 2016). It was characterized as having small-sized plants, ovate leaves 0.5–1.0 mm long, with acute apices, weakly recurved margins, costa ending few cells below leaf apex, and smooth laminal cells. A singe ITS accession of D. mongolicus is represented in GenBank; it belongs to the holotype specimen. In our analysis it was resolved within clade 5, in a moderately supported (PP 0.95, BS 99) clade with 8 specimens from Russia (southern Siberia, Yakutia and Dagestan in the Caucasus). These specimens are partially in agreement with the description of D. mongolicus morphologically, including plant size, leaf shape, and unistratose, narrowly recurved leaf margins; their leaves are only slightly larger than it was provided in the original description of this species. Four specimens (from Tyva and Dagestan) also have smooth laminal cells, whereas the rest four specimens (from Yakutia, Altai and Dagestan) have laminal cells with clear, round papillae on dorsal surface ( Fig. 4 ). In the molecular phylogenetic tree, type specimen of D. mongolicus forms a small, moderately supported subclade with two specimens, one of them, from Tyva being most similar to it (leaves ca. 0.8 mm long, smooth laminal cells), while another one, from Yakutia, having leaves ca. 1.1 mm long and laminal cells papillose dorsally. Jiménez (2006) states that leaf papillosity is an important morphological character for species distinguishing in Didymodon , but in some species leaf cells are always smooth or always papillose, but there are several species in Europe, North Africa and West Asia which may have smooth or papillose laminal cells: D.

Figures

Fig. 4. Leaves and leaf transverse sections of Didymodon mongolicus (from Russia, with isolate numbers). For specimen 4107 from Tyva Republic (OK4107) perichaetial leaf is also shown. Scale bars: 1 mm for leaves; 100 µm for leaf transverse sections.