Didymodon hengduanensis

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 : 138

Didymodon hengduanensis

This species was described in 2016 from Hengduan Mts (Yunnan, China) and was also found in Sichuan Province. Its distinctive characters include ovate-lanceolate leaves with comparatively wide bases, unistratose, recurved to revolute margins, percurrent costae, sparsely papillose laminal cells, and basal marginal cells in several rows oblate, with thickened transverse walls. Its five GenBank accessions formed a fully supported clade within clade 4, in which two specimens from Russia were resolved: one from Primorsky Territory, another from Irkutsk Province. These two specimens also fitted D. hengduanensis morphologically. They are described, illustrated and discussed in the Taxonomy section .

A potentially undescribed species revealed in the present analysis (see also discussion on D. acutus above)

(1) Two specimens from Primorsky Territory (isolates OK 3317 and OK4019) formed a maximally supported clade sister to one GenBank accession called D. icmadophilus from China, Heilongjiang (PP 0.94; BS 97). Their mutual clade was resolved as sister to D. wisselii clade without support, within clade 5. In some characters (excurrent costae, papillose leaf cells) plants from Primorsky Territory actually resembled D. icmadophilus , but they had leaves different in shape, widely spreading but not erect-patent when wet, and papillae on laminal cells small, sparse, present on both leaf surfaces. Their relationship to European D. icmadophilus was also not confirmed by molecular data, as the latter species was resolved in the clade 4 in our study, far from the specimens in question. These plants are described in the Taxonomy section under the name D. cherdantsevae .

(2) Four specimens (isolates OK3477, OK3484, OK4053, and OK4101) from distant localities (Primorsky Territory, Yakutia, Dagestan) formed a maximally supported clade within clade 5, without obvious relationship with other species. They were uniform morphologically and resembled D. cordatus in having leaves with highly recurved margins, similar costa structure, papillose laminal cells and presence of multicellular axillary gemmae; however, they had different leaf shape, with scarcely differentiated bases, and their leaf margins were only slightly recurved but not revolute. These differences together with an evidence from molecular markers suggested that this is an undescribed species; it is described in the Taxonomy section as D. calciphilus .

(3) Nine specimens from southern Siberia (Irkutsk Province, Buryatia, Zabaikialsky Territory, Khakassia, and Altai Republic, isolates OK3321, OK3455, OK3457, OK3474, OK3475, OK3489, OK3496, OK3519, and OK4103 formed a maximally supported clade sister to D. mongolicus -clade within clade 5. They are characterized by having deltoid leaves with margins revolute almost to apices, papillose laminal cells, costae in transverse section with 2–3 layers of guide cells and no ventral stereids, and multicellular axillary gemmae occasionally present. This combination of characters partially resembled D. cordatus , D. tectorum and D. desertorum , but did not exactly fit any of these species. This fact, together with data from ITS, convinced us that this is a new species. It is described in the Taxonomy section as D. baicalensis .

(4) Three specimens (isolates 3449, 3454 and 4108) from the Caucasus, Tyva and Yakutia were resolved within clade 4 in a highly supported (PP 1, BS 0.99) clade sister to D. hengduanensis , with low support for their mutual clade (PP 0.72, BS 57). These specimens are characterized by leaves tightly appressed when dry, straight, ovate-triangular, with long excurrent costae, fragile apices and unistratose laminae. This character combination is unique in Didymodon s. str. ; thus these plants are described as a new species, D. abramovae in the Taxonomy section. Another three specimens with the same morphological characters (isolates OK3451, OK3452 and OK4112) from Perm Territory, Ingushetia and Tyva were found in a grade at the base of fully supported D. borealis -clade. We tentatively refer them to D. cf. abramovae .

(5) One morphologically very peculiar specimen from Altai Republic (isolate OK3893) was resolved in an orphaned position. Despite only one such specimen was found, it is so distinct in morphology, that we decided to describe it in order to attract attention to it and make search of similar plants easier. It is described in the Taxonomy section as D. truncatus .

Species that could be expected in the territory of

Russia but not found in the present analysis