John R. Spence

Plants small to large, in open to dense turfs or gregarious, green, yellow-green, pink, or red. Stems 0.1-2(-3) cm, gemmiform to evenly foliate, not or strongly branched; rhizoids usually few, micronemata present, macronemata few or absent. Leaves imbricate to loosely set and slightly twisted when dry, spreading when moist, ovate, ovate-lanceolate, or triangular, flat or concave, 0.4-2.5(-3) mm; base rarely decurrent; margins plane to strongly revolute, entire to serrulate distally, 1-stratose, limbidium absent or weak; apex broadly rounded to acuminate; costa not reaching apex to long-excurrent, awn present, apiculus occasionally present, guide cells usually in 1 layer; alar cells quadrate; laminal areolation heterogeneous; proximal laminal cells gradually or abruptly quadrate to rectangular, , 1-2(-4):1; medial and distal cells rhomboidal to elongate-hexagonal, <8-16(-20) µm wide>, usually (3-) 4-8:1, walls thin to moderately incrassate, not porose. Specialized asexual reproduction common, of several types, including leaf axil bulbils or brood branchlets, rhizoidal filiform gemmae and tubers, and stem tubers. Sexual condition dioicous or rarely synoicous; perigonia and perichaetia terminal; perigonial and perichaetial leaves not much differentiated, outer leaves larger, inner leaves smaller than leaves of innovations. Seta usually single, straight or somewhat flexuose, not geniculate. Capsule erect, inclined, or nutant, pyriform or ovate, , 1-3(-5) mm; hypophysis slender or thick, ; operculum short-conic to long-convex, sometimes apiculate or rarely rostrate; peristome double; exostome yellow to brown, teeth lanceolate, acuminate; endostome rarely adherent to exostome, basal membrane high to low, segments well developed or occasionally reduced, perforations lanceolate to ovate, cilia long and appendiculate to short or absent. Spores shed singly, 8-18(-20) µm, smooth to papillose, light brown.

Species ca. 100 (19 in the flora): nearly worldwide; tropical, subtropical, temperate to boreal regions.

Species of Gemmabryum are small and often sterile, and can be extremely difficult to identify in the absence of gemmae. This genus exhibits a remarkable array of asexual reproductive structures, including bulbils, rhizoidal tubers, stem tubers, and filiform rhizoidal gemmae. Sterile collections should be made whenever possible, as fertile material often lacks the diagnostic gemmae.