Roellia Kindberg, Gen. Eur. & North Amer. Bryin. 37. 1897.
Plants large, stems erect, 2--4 cm. Leaves shiny green above, large, 3--8 mm, obovate, rosulate, acute, margins bordered by thickened elongate cells, serrate by projecting cell ends, distal-medial lamina cells large and hexagonal, to 150 mm, basal cells more regularly rectangular, often somewhat narrower and longer than cells above, costa lacking stereid band or a few cells present. Specialized asexual reproduction lacking. Sexual condition dioicous. Capsule inclined to pendant, elongate-cylindric, occasionally curved, yellow-brown, peristome well developed, exostome teeth lanceolate-acuminate, papillose, narrowly bordered, trabeculate, endostome with high basal membrane, segments keeled, perforate, cilia long, 2--4, nodose. Spores small, 10--15 mm, smooth or finely papillose.
Species 1 (1 in the flora): w North America.
Roellia is a large, distinctive taxon endemic to and common in high elevation and other cool-climate forests of western North America, where it typically occurs on litter under dense shade. The taxonomic placement of R. roellii has long been debated. Early workers placed the species in either Mnium or Bryum, while more recently it has been moved to the monotypic genus Roellia and placed in the Bryaceae, primarily because of laminal areolation. Although Roellia is morphologically similar to Rhodobryum and Rosulabryum, recent DNA studies suggest that it is closer to the Mniaceae than the Bryaceae. Superficially, under the light microscope, the species looks distinctly mniaceous. It may be best placed in a family of its own. Roellia is similar to species of Rhodobryum, but differs in its much larger lamina cells and leaves that are shrunken but not strongly contorted and twisted when dry.