The opening fan: integrative taxonomic revision of Sphagnum fimbriatum and S. concinnum in North Asia

Sphagnum mosses represent an essential component of boreal, arctic, and alpine wetland ecosystems; however, North Asia remains insufficiently sampled in recent studies on Sphagnum. We have revised over 300 specimens assigned to S. fimbriatum and S. concinnum from Northern Eurasia to assess their distribution patterns. We employed an integrative taxonomic approach combining molecular phylogenetics, and traditional and geometric morphometrics to investigate the observed morphological variation within them for taxonomic consistency and clarify affinities of ambiguous morphotypes. It corroborated the delimitation of the already known species and revealed two previously unrecognized lineages. These are genetically and morphologically distinct from S. fimbriatum and S. concinnum and are described here as the new species S. fedosovii sp. nov. and S. gelidum sp. nov. The four species differ in habit, apical bud visibility, size and shape of stem leaves, and branch leaf pore pattern. Affinities inferred from the nuclear marker RAPDb may indicate S. gelidum as a probable paternal ancestor of S. arcticum and S. olafii. Moreover, our results showed the previously unnoticed heterogeneity of S. fimbriatum, with the north Asian plants bearing a distinct haplotype. The two newly revealed species occur in continental North Asia, in areas with low precipitation rate and strong temperature seasonality, while S. fimbriatum showed a predominantly boreal distribution and S. concinnum appeared mainly restricted to the Arctic seashore. Descriptions, illustrations, and species identification keys are provided. The newly described species, as well as S. concinnum, might be especially sensitive to climate change, which is driving vegetation shifts across the Arctic and Hypoarctic.