Ignatova, E.A., I.V. Czernyadjeva, A.V. Fedorova & M.S. Ignatov. 2021. A morphologocal and molecular phylogengetic study of the genus Calliergon (Calliergonaceae, Bryophyta) in Russia

Arctoa (2021) 30: 8–24

doi: 10.15298/arctoa.30.02

The genus Calliergon is usually accepted in the Northern Hemisphere with only four widespread species and 1–2 less well-known ones, but nevertheless practical identification work often ends with specimens that are difficult to identify. This is especially so in Asian Russia, where combinations of character states in many plants do not always fit the classical treatments for Europe and North America. Especially problematic are dioicous plants with large alar groups and a thin costa. Such morphotypes prevail in some northern regions of Siberia. A molecular phylogenetic tree based on ITS and rpl16 placed such plants in a grade with clades of C. giganteum s.str. and C. megalophyllum nested within. The differences from C. giganteum and C. megalophyllum are moderately sharp and stable, thus we suggest segregation the northern Siberian plants as a subspecies, C. giganteum subsp. sibiricum Ignatova & Czernyadjeva. Calliergon cordifolium populations from high Arctic are differentiated by nrITS, and some of these plants have very broad leaves and fit the concept of C. orbicularicordatum, but other plants of the same haplotype are morphologically identical to Calliergon cordifolium s.str., precluding acceptance of C. orbicularicordatum at the species level. Far Eastern populations of Calliergon cordifolium s.l. appeared to be most sharply differentiated in both ITS, rpl16 and morphology by exceptionally well differentiated leaf borders. However, taxonomic segregation seems unwise due to enormous variation in these populations.