Towards a new classification of the Bryaceae: revealing a sister lineage to <i>Ptychostomum</i> and assessing <i>Gemmabryum</i>

Introduction The family Bryaceae, including its largest genus Bryum, underwent several reclassifications during the past few decades. As part of a new taxonomic revision based on molecular and morphological data, we reinstate several Gemmabryum species in Bryum. In addition, two species previously included in Gemmabryum and Rosulabryum are transferred to Ptychostomum.Methods Our molecular phylogenetic analyses are based on nuclear ITS and chloroplast rpoC2, ndhF and rps14–psbZ sequence data of 52 Bryaceae species. The collected morphological character states of the taxa examined are visualised in a representative heatmap.Key results and conclusions The results of the maximum-likelihood and Bayesian inference analyses showed almost identical generic groups. Rhodobryum is closely related to a group of early-diverging species, most of which belong to Rosulabryum. Distinct morphological features and a preference for warmer climates are consistent with this. The other Rosulabryum taxa, R. erythroloma and R. rubens, were recovered as members of a sister clade to Ptychostomum. An inclusion of the type R. albolimbatum in future studies will clarify whether a definition of a new genus for one of the two Rosulabryum groups is adequate. According to new molecular data, we reinstate the Gemmabryum species in Bryum because the type B. argenteum is recovered within the same group. The position of Gemmabryum caespiticium and Rosulabryum sanguilentum in the Ptychostomum group requires a transfer of these two species to this genus.