w North America.
Plants of Roellobryon are large, distinctive mosses found in high-elevation and cool-climate forests of western North America, typically on litter in dense shade. The taxonomic placement of R. roellii has long been debated; early workers placed the species in either Bryum or Mnium, while more recently it has been segregated as a monotypic genus and placed in Bryaceae, primarily because of its distinctive laminal areolation. Although Roellobryon is morphologically similar to Rhodobryum and Rosulabryum, recent molecular studies suggest that it is closer to Mniaceae than Bryaceae. Superficially, under the light microscope, the species looks distinctly mniaceous; it is best placed in its own family. Recently, R. Ochyra (2011) pointed out that the previously used genus name, Roellia Kindberg, is an orthographic variant of Roella Linnaeus, a genus in the Campanulaceae, and the name Roellobryon replaces Kindberg’s name. Roellobryon is similar to species of Rhodobryum of the flora, but differs in the much larger laminal cells and leaves that are rugose and shrunken but not strongly contorted and twisted when dry.