Ignatov, M.S., J. Kučera, L. Hedenäs, O.I. Kuznetsova & E.A. Ignatova. 2020. A revision of the genus Orthothecium (Plagiotheciaceae, Bryophyta) in northern Eurasia

Arctoa (2020) 29: 10–48

doi: 10.15298/arctoa.29.02

A revision of the genus Orthothecium involving a molecular phylogenetic approach was performed based on material from northern Eurasia with a particular focus on the territory of Russia. It showed that diversity of the genus in Asian Russia, and particularly in the permafrost regions of Siberia was strongly under-recorded if labelled with names of European species. While all five currently accepted European species occur in Asian Russia (although O. rufescens probably only reaches European-Asian borders), four additional species need to be described as new to science: O. brunnescens, O. retroflexum, O. remotifolium and O. sibiricum. The ranges of O. lapponicum, O. chryseon, O. intricatum and O. rufescens are discussed and revised. Orthothecium strictum and O. intricatum harbour a surprisingly high genetic diversification, however, the phylogenetic signal from analysed chloroplast and nuclear loci shows a reticulate pattern, which does not allow for drawing unequivocal taxonomic conclusions; moreover, the morphological characters are not fully consistent with the intraspecific molecular lineages and show mostly a clinal type of variation, hence we have refrained from description of additional species or intraspecific taxa. Incomplete lineage sorting has been documented in several cases between O. sibiricum and O. lapponicum and between O. intricatum and O. rufescens. Such specimens often show an intermediate morphology.