Ignatov, M.S., O.I. Kuznetsova, V. Hugonnot, V.E. Fedosov & E.A. Ignatova. 2023. The genus Fissidens in Russia. I: species of Fissidens monguillonii affinity

Arctoa (2023) 32: 59–74

doi: 10.15298/arctoa.32.06

A preliminary molecular phylogenetic analysis of Fissidens species of the F. bryoides-complex revealed one species with a relatively weak uni- to bistratose libmidium nested in a clade in which almost all the samples have stout multistratose limbidia. It is a well-defined species, relatively widely distributed in European Russia, in scattered localities eastwards to the Urals. In its nuclear ITS DNA sequences it is most similar to F. monguillonii from Altantic Europe. However, it is a much smaller plant, resembling small phenotypes of F. viridulus, and unlike F. monguillonii it has a weak uni- or bistratose limbidium. This Fissidens species is described as a new species, F. mosquensis. The clade formed by F. monguillonii and F. mosquensis further includes the East Asian F. lateralis (=F. bryoides var. lateralis), a species also characterized by a multistratose limbidium and perichaetial leaves narrower than stem leaves. Fissidens mosquensis is compared with F. bryoides and several morphotypes of F. viridulus s.l. A terrestrial form of F. rivularis from the Caucasus with a uni- to bistratose leaf margin is also discussed. Plants with this combination of traits are nested in a clade in which the other samples represent aquatic F. rivularis.