Sp. Musc. Frond. Suppl. 2(1,2): 131, plate 135. 1824.
Plants small, in open to dense turfs or dense cushions, dark green to golden. Stems 0.5–2 cm, rosulate or sometimes gemmiform, sparsely to strongly branching by subfloral innovations; rhizoids few-to-many, micronemata often present on stems. Leaves imbricate to spirally twisted around stem when dry, erect-spreading when moist, broadly ovate, concave, 0.6–2 (–3) mm, smaller proximally; base not or weakly decurrent; margins plane or revolute proximally, entire to serrate distally, 1-stratose, limbidium absent or present; apex acute to broadly rounded; costa short to long-excurrent, awn stout, pigmented, denticulate, stereid band well developed, guide cells present; alar cells usually similar to juxtacostal cells; laminal areolation heterogeneous; proximal laminal cells quadrate to short-rectangular, 1–2: 1; medial and distal cells short-rectangular to irregularly hexagonal, 2–4: 1, walls thin to somewhat thick, not pitted. Specialized asexual reproduction by rhizoidal tubers or absent. Sexual condition dioicous; perigonia and perichaetia terminal; perichaetial leaves same size as vegetative leaves or usually larger, sometimes forming rosette, inner leaves highly differentiated, often narrower. Seta single, straight. Capsule erect to suberect, elongate-ovate to subcylindric, 1–3 mm; hypophysis slender to well differentiated; operculum short to long-conic; peristome double; exostome redbrown proximally, pale-brown distally, teeth linear-lanceolate; endostome reduced, separate from exostome, basal membrane low, segments absent or short and blunt, not perforate, cilia rudimentary or absent. Spores shed singly, 12–18 µm, smooth or papillose, pale tan to brown.
Nearly worldwide, tropical and subtropical regions, primarily paleotropical
Species ca. 30 (2 in the flora).
Typical Brachymenium consists of subtropical-tropical epiphytes with gametophytes similar to those of Rosulabryum. Brachymenium andersonii has been reassigned to Rosulabryum, while B. exile (Dozy & Molkenboer) Bosch & Sande Lac. is now placed in Gemmabryum near the G. bicolor complex. Brachymenium niveum and B. systylium have been transferred to the newly erected Leptostomopsis, of which the latter is the type. The remaining North American species, B. macrocarpum and B. mexicanum, are probably not closely related to the type section of Brachymenium. H. Ochi (1980) placed B. macrocarpum in sect. Peromnium (Mitten) Brotherus, along with B. jamesonii Taylor and B. regenellii Hampe. This group is similar to some species of Gemmabryum, especially the paleotropical G. coarctatum (Bosch & Sande Lacoste) J. R. Spence & H. A. Ramsay, but differs in the presence of bulbils and strongly rosulate, twisted leaves. Uncertainty in the phylogenetic relationships of the section has B. macrocarpum tentatively retained in Brachymenium pending further study. Brachymenium mexicanum seems to be related to B. macrocarpum, although it also shows similarities to species of the type section. The genus description above is largely based on Brachymenium sect. Peromnium.
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