• Mohamed, H. 1979. A taxonomic study of Bryum billardieri Schwaegr. and related species. J. Bryol. 10: 401–465.
• Ochi, H. 1980. A revision of the neotropical Bryoideae, Musci (First part). J. Fac. Educ. Tottori Univ., Nat. Sci. 29: 49–154.
• Spence, J. R. 2014. Bryaceae. 28: Pp. 117–185. In Fl. N. Amer. Oxford University Press, New York.
• Allen, B. H. 2002. Moss flora of Central America, Part 2. Encalyptaceae–Orthotrichaceae. Monogr. Syst. Bot. Missouri Bot. Gard. 90: viii + 699 pp.
• Ochi, H. 1994. Bryum in A. J. Sharp et al. (editors), Moss Flora of Mexico. Mem. New York Bot. Gard. 69: 454–489.
• Spence, J. R. 2020. Studies in Austral Bryaceae (Bryopsida) II. New combinations in Rosulabryum J.R. Spence from Madagascar and South America. Bryoph. Diversity & Evol. 42(1): 61–64.

Bryum is the largest genus of the family and estimated at nearly 800 species distributed worldwide. About 50 species are estimated for the Neotropics; the tropical Andes estimated at 43 species. The genus for all the tropical Andean countries is mostly found in open or forested premontane to high montane, extending into the páramo and puna. Relatively few species of Bryum are found in the lowlands. The genus is admittedly one of the most difficult genera of mosses. A highly variable genus, both gametophytically and sporophytically; plants are typically terrestrial, leaves variable, ovate, oblong, obovate to lanceolate, margins weakly to strongly bordered, laminal cells broad, hexagonal, very rarely oblong-linear, and with a well developed peristome, rarely reduced. In addition to the references of Mohamed (1979) and Ochi (1980), the treatments for Mexico (Ochi 1994) and Central America (Allen 2002) are very helpful. Keys modified from Ochi (1980).

Bryum es el género más numeroso de esta familia y se estiman casi 800 especies distribuidas en todo el mundo. Aproximadamente 50 especies están presentes en el Neotrópico; los Andes tropicales estimados en 43 especies. Este género en general en todos los países andinos tropicales generalmente se encuentra en el bosque premontano hasta bosque montano alto o zonas abiertas, extendiéndose hasta el páramo y puna. Relativamente pocas especies de Bryum se encuentran en tierras bajas. Hay que admitir que este es uno de los géneros más difíciles de los musgos. Un género muy variable, respecto al gametofito y el esporofito; las plantas son típicamente terrestres, con hojas variables, ovadas, oblongas, obovadas hasta lanceoladas, márgenes débilmente hasta marcadamente bordeados, células de la lámina anchas, hexagonales, muy rara vez oblongo-lineales y con el peristoma bien desarrollado, rara vez reducido. Además de las referencias de Mohamed (1979) y Ochi (1980), los tratamientos para México (Ochi 1994) y América Central (Allen 2002) son muy útiles.

Recent studies have attempted to provide a more natural grouping, recognizing a number of segregate genera (see Spence 2014). At least some of these segregate genera have a core of characters, e.g. julaceous leafy stems, preponderance of asexual reproduction, or simply in stature, large plants. However these segregate genera are also, to a degree, ill-defined as the traditional concept of Bryum with apparently no unique features. Provided below are the six segregate genera accompanied by a short diagnosis and number of species present among the tropical Andean countries. At least 30 species can be assigned to one of six genera; however there are at least 13 species that are unassigned. In summary the following six genera can be recognized with the number of species: Bryum 5, Gemmabryum 6, Imbribryum 5, Plagiobryoides 3, Ptychostomum 4, and Rosulabryum 7.

Bryum and Segragate Genera

Bryum (sensu stricto)

Plants small, mostly less than 1 cm, stems julaceous or gemmiform, leaves strongly imbricate, concave, margins mostly entire, border usually absent. The coloration is generally distinctive, with Bryum argenteum Hedw. and related species silver or whitish, whereas Bryum chryseum Mitt. is golden-yellow. Number of species 5, possible additional species 1-2. Representative species: Bryum argenteum Hedw., B. chryseum Mitt., B. ellipsifolium Müll. Hal.

Gemmabryum

Plants are quite variable, mostly small to medium sized, leaves ovate-lanceolate or triangular, margins entire to weakly serrulate distally, border absent or weak, costa typically short to long excurrent, alar cells often quadrate. The distinctive feature is the various forms of asexual reproduction including rhizoidal filiform gemmae, axil bulbils or brood branchlets and tubers. Number of species 6. Representative species: Bryum apiculatum Schwägr., B. caespiticium Hedw., B. coronatum Schwägr., B. dichotomum Hedw.

Imbribryum

Plants are equally foliate, with strongly imbricate leaves, ovate to lanceolate or triangular- lanceolate, border weakly developed to absent, costa percurrent to short excurrent, upper cells mostly firm-walled or thick, and well developed peristome. Mostly high open montane to páramo and puna, often associated with semi-aquatic or aquatic habitat, on soil and rocks. Number of species 5, possible additional species 3. Representative species: Bryum alpinum Huds. ex With., B. laevigatum Hook. f. & Wilson, B. microchaeton Hampe.

Plagiobryoides

Plants somewhat small, to 1.5 cm, rarely more, leaves mostly ovate, apices obtuse to broadly acute, base often slightly decurrent, margins entire, border weak to distinct or colored. The common B. limatum and less frequent B. renauldii are often associated with semi-aquatic habitats such as stream banks. Number of species 3. Representative species: Bryum cellulare Hook., B. limbatum Müll. Hal., B. renauldii Röll

Ptychostomum

Plants mostly medium sized, leaves often contorted and twisted when dry, ovate-lanceolate, apices acuminate to acute, base decurrent or not, margins often revolute and entire or weakly tooth near apex, bordered (often obscured by revolute margins), costa mostly short to long excurrent. Number of species 4. Representative species: Bryum algovicum Sendtn. ex Müll. Hal., B. pallescens Schleich. ex Schwägr., B. pseudotriquetrum (Hedw.) G. Gaertn., B. Mey. & Scherb.

Rosulabryum

Plants mostly large, usually strongly rosulate, sometimes in 2 or more interrupted rosettes, less often evenly foliate, leaves ovate, oblong-lanceolate, obovate, or spathulate, 3.5-6 mm, border weak to strong, rarely absent, margins serrate, rarely weakly so. At least among some of the species asexual reproduction includes cylindrical and strongly papillose gemmae or deciduous flagellate innovation branches. More than half of the members of this taxon are the principle montane forest species of the Bryum segregate genera. Number of species 6. Representative species: Bryum atenense RS. Williams, Bryum andicola Hook., B. capillare Hedw., B. densifolium Brid., B. richardsii Sharp, Bryum spininervium Broth.

Bryum y Géneros Segregados

Estudios recientes han intentado brindar una clasificación más natural, reconociendo varios géneros segregados (ver Spence 2014). Al menos algunos de estos géneros segregados tienen características comunes, e.g. tallos con hojas juláceas, preponderancia de reproducción asexual, o simplemente en estatura, plantas grandes. Sin embargo, estos géneros segregados, en cierto grado, están mal definidos siguiendo el concepto tradicional de Bryum, aparentemente no tienen características exclusivas. A continuación se presentan seis géneros segregados acompañados por un diagnóstico breve y el número de especies presentes en los países de los Andes tropicales. Por lo menos 30 especies pueden ser asignadas a uno de seis géneros; no obstante por lo menos hay 13 especies que aún no han sido asignadas. Los números de especies aceptadas para los siguientes siete géneros son: Bryum atenense RS. Williams, Bryum andicola Hook., B. capillare Hedw., B. densifolium Brid., B. richardsii Sharp, Bryum spininervium Broth.

Bryum (sensu stricto)

Plantas pequeñas, generalmente menores a 1 cm, tallos juláceos o gemiformes, hojas marcadamente imbricadas, cóncavas, márgenes generalmente enteros, frecuentemente sin borde. La coloración generalmente es distintiva, con Bryum argenteum Hedw. y especies relacionadas plateadas o blanquecinas, mientras que Bryum chryseum Mitt. es amarillo-dorada. Número de especie 5, posiblemente hay 1-2 especies adicionales. Especies representativas: Bryum argenteum Hedw., B. chryseum Mitt., B. ellipsifolium Müll. Hal.

Gemmabryum