Didymodon validus

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 validus

This species was described from Austria ( Limpricht, 1888). In Europe it is considered as vulnerable; its presence is confirmed only in France, Italy, Slovakia (Hodgetts & Lokhart, 2020) and Poland ( Jiménez et al., 2022). It remained neglected in Russia, probably because Savicz-Lyubitskaya & Smirnova (1970) treated it as a variety of D. rigidulus , and it was mainly ignored by those who identified collected specimens. This name became in use by Russian bryologists only recently, and many Didymodon specimens from the Caucasus and Asian Russia, having leaves with unistratose, weakly recurved margins, sharply acuminate apices, and smooth laminal cells, were identified as D. validus . However, in many cases this name was supplemented with “s.l.” or “cf.” remarks due to a considerable variability of these specimens in leaf size, leaf base differentiation, length of acumina, and leaf stature in dry and wet condition.

In the analysis by Jiménez et al. (2022), one specimen from China, Xinjiang appeared in a clade with European specimens of D. validus ; it hinted on the possible wider distribution of this species in Asia, but its morphological circumscription needed to be clarified. For the present analysis, 19 specimens identified as D. cf. validus or D. icmadophilus were sampled; they were resolved in a moderately supported (PP 1, BS 79) clade together with all available GenBank accessions of D. validus . This clade appeared in a sister position to D. wisselii & D. schensianus clade. A selection of specimens in a D. validus - clade represents plants from a wide geographical range: Central European Russia, Caucasus, Urals, Altai Mts in southern Siberia, different regions of Yakutia, Amur Province, Khabarovsk and Primorsky Territory in the south of Russian Far East. In their main morphological characters, they do not contradict the description and illustrations of D. validus provided by Jiménez (2000).

Leaves and transverse sections of the sequenced specimens of D. validus are shown in Fig. 3. Most of these specimens have leaves with scarcely differentiated bases, without shoulders, gradually tapered into narrow acumina, having weakly recurved margins and shortly excurrent costae. Specimens from European Russia, including Urals and Caucasus, and one sample from central Yakutia have shorter (1.4–1.9 mm long) leaves than most oth- er specimens from Asian Russia (2.2–2.9 mm long). However, all these measurements are within the range of variability of this species given by Jiménez (2000): (1.2–) 1.6–2.7(–3.2) mm. Thus, the presence and wide distribution of D. validus in Russia is confirmed.

Noteworthy, according to Jiménez (2006), sexual condition and sporophytes are unknown in D. validus . Most of our sequenced specimens were also sterile, and only in two specimens, OK3464 from Yakutia (Ust-Nera) and OK4063 from Altai (Chemal) sporophytes were found. However, we failed to find any male inflorescences in these or other specimens. Sporophytic characters of D. validus are described in the Taxonomy section. Jiménez (2000) also mentioned that round multicellular gemmae are often present in leaf axils in D. validus ; in our sequenced specimens gemmae were very rare.