Plants: small to large, in open to dense low turfs or gregarious (tall turfs in R. andersonii), green to red-green. Stems: 0.3–6 cm, usually strongly rosulate, sometimes in 2 or more interrupted rosettes, rarely evenly foliate or subjulaceous, subfloral innovations common; rhizoids often many, micronemata and macronemata present. Leaves: variously contorted to spirally twisted around stem when dry or rarely nearly imbricate, erect to erect-spreading when moist, ovate, obovate, or spathulate, flat or weakly concave, 0.4–4.5 mm; base sometimes decurrent; margins recurved proximally or sometimes plane, plane distally, nearly entire to distinctly serrate near apex, 1-stratose, limbidium present or absent; apex broadly rounded to acute; costa sometimes not reaching apex, usually short- to long-excurrent, awn pigmented or hyaline, stereid band well developed, guide cells present, in 1 (or 2) layers; alar cells not differentiated; laminal areolation heterogeneous; proximal laminal cells rectangular, longer than more distal cells, 2–4:1; medial and distal cells rhomboidal, 3–5:1, walls thin to thick, sometimes porose. : Specialized asexual reproduction common, by rhizoidal tubers or filiform leaf axil gemmae. Sexual: condition dioicous, rarely synoicous, polyoicous, or autoicous; perigonia and perichaetia appearing terminal or lateral; perigonial leaves often enlarged and distinctly rosulate; perichaetial leaves same size as vegetative leaves, not forming rosette, inner leaves differentiated, more acuminate. Seta: single, rarely double or triple, straight. Capsule: nutant to inclined, clavate to cylindric or rarely pyriform, 2–6 mm; hypophysis little differentiated; operculum short-conic to umbonate; peristome double; exostome yellow, teeth lanceolate to narrowly lanceolate; endostome well developed, not adherent to exostome, basal membrane high, 1/2–2/3 exostome length, segments same height as exostome, widely perforated, cilia 2 or 3, appendiculate. Spores: shed singly, 8–20 µm, smooth to finely papillose, dark yellow. Nearly worldwide, concentrated in the Southern Hemisphere, especially Africa, and in subtropical to tropical mountains.
Species ca. 80 (13 in the flora). Rosulabryum is a large, distinctive genus mainly found in tropical mountainous areas and in the Southern Hemisphere in areas of seasonal temperate climates, occurring typically on soil, less commonly on rock or wood, rarely epiphytic. The center of diversity appears to be sub-Saharan Africa. Most Northern Hemisphere bryologists are not familiar with the great morphological diversity of the species of Rosulabryum sect. Rosulabryum, traditionally placed in Bryum sect. Rosulata (Müller Hal.) J. J. Amann, as very few taxa extend beyond 20° N latitude. The most widespread representatives of Rosulabryum in the Northern Hemisphere are the small somewhat atypical species of Bryum sect. Trichophora J. J. Amann centered on R. capillare. Recent molecular work suggests that this section of Rosulabryum may be closer to Ptychostomum, and thus convergent on the robust Rosulata clade of the genus. However, very few species have been sampled for molecular work, and it seems unlikely that the complex of characters defining Rosulabryum could have evolved twice in unrelated clades. Plants of Rosulabryum have concolorous leaf apices and symmetric capsules. The rhizoidal tubers, when present, are spheric; the endostome is papillose.