AbstractComparative studies of North European Isobryalean and Hypnobryalean mosses have shown that axillary rhizoids occur only inMyurella, Platydictya jungermannioides, Orthothecium, Isopterygium muellerianum, I. alpicola, I. pulchellumandHerzogiella.These taxa also share the following features: purple and granular-papillose rhizoids, easily detached branches, rather weak and not plicate perichaetial leaves, whitish-yellow exostomes with borders never distinctly widened at the zone of transition in pattern between the lower and upper part of the outer peristomial layer. In all characters except rhizoid position and, in some species, stem leaf areolation, this group of taxa is very similar to certainPlagiotheciumspecies and toIsopterygium elegans.It seems probable that all these taxa are closely related and should be placed in a single family, the Plagiotheciaceae.