Rosulabryum J.R.Spence

Plants medium-sized to robust, bright, yellow-, or brown-green, weakly lustrous, usually comose ("rosulate"), often serially. Stems red-brown, often branched by innovations arising within or below perichaetia, beset with red-brown, densely papillose rhizoids, in cross-section with firm-walled cortical cells and a distinct central strand. Leaves mostly enlarged and comose at stem apices, sometimes evenly spaced on sterile stems, wide- or erect-spreading when moist, twisted around the stem or less often spiralled around their own axis when dry, widest above the middle, obovate or spathulate, ± narrowed at base, abruptly tapered to a cuspidate, awned, or piliferous apex, sometimes reflexed apically, weakly or strongly bordered and ± recurved at margins, sharply serrate, denticulate or rarely entire, not decurrent; upper laminal cells hexagonal to ± short rhombic, firm- or less often thin-walled, strongly or weakly porose, becoming more oblong, and usually more porose towards leaf base; marginal cells differentiated, linear, and mostly pale, forming a distinct border that fuses with cells of the leaf apex or fades near the leaf apex; basal cells usually brown. Costa mostly brown, strong, either fusing with the cells of the apical cusp or excurrent to form an awn. Brood bodies (tubers or filamentous axillary gemmae) often present.

Dioicous or less often synoicous or polygamous. Perichaetia terminal and comose or rarely at the plant base. Perigonia terminal. Setae single or multiple (to 4 per perichaetium), red, cygneous and sometimes strongly hooked just below the capsule; capsules cernuous or pendent, narrowly cylindric or oblong-cylindric, with a well-defined or ill-defined and usually curved neck; operculum mammillate, with or without an apiculus. Peristome double and often perfect; exostome teeth yellow-brown or pale; endostome with a high basal membrane, narrowly perforate or sometimes fenestrate segments ± equal in height to the teeth; cilia well-developed, 2–4, appendiculate or occasionally nodose. Calyptra cucullate and smooth. Spores spherical, c. 11–21 µm in N.Z. species.

The genus Rosulabryum was erected by Spence (1996) to accommodate the rosulate species placed by Ochi (1992) in his sect. Capillaria, subsections Capillaria and Rosulata. According to Spence, those species "share several features that in combination distinguish them from other groups in the broadly conceived genus [Bryum]. These include obovate, twisted or contorted leaves; usually distinct leaf border with marginal teeth; rhizoidal tubers; filiform gemmae in leaf axils; and inclined to nutant capsules with unreduced peristomes."

Spence’s concept of Rosulabryum is followed here, despite the consequent equivocal placement of R. capillare (Hedw.) J.R. Spence, which is accepted here with reservation; this species is anomalous in the genus in respect to several characters, including sexuality, perichaetial position, capsule shape, and operculum shape.