Bryum is a genus of mosses in the family Bryaceae. It was considered the largest genus of mosses, in terms of the number of species (over 1000), until it was split into three separate genera in a 2005 publication. As of 2013, the classification of both Bryum and the family Bryaceae to which it belongs have undergone significant changes based on recent DNA studies.
Bryum is a polyphyletic genus that has high morphological variation. Bryum species generally have shorter laminal cells with short, thick, and rounded stems. All Bryum species exhibit narrowed cells at the margins. Bryum species can be identified through patterns of asexual reproduction, coloration features of the stem and leaf base, and the strength of the leaf border.
Botanist John R. Spence published a reclassification of the genus in 2005. The genus Ptychostomum was reinstated, while the genera Leptostomopsis, and Plagiobryoides were created. The genera Gemmabryum, Imbribryum, and Rosulabryum were later published to further divide Bryum.
- New genera and combinations in Bryaceae (Bryales, Musci) for North America, J. R. Spence, Phytologia 87: 15-28 (2005)
- Genus Bryum, California Moss eFlora, Jepson eFlora for CA Vascular Plants, University Herbarium, University of California, 
- "Bryum". eFloras. Flora of North America. Retrieved 26 October 2019.
- Sp. Musc. Frond. 178, plate 42, figs. 8-12; plates 43, 44. 1801
- Spence, John R. (April 2007). "NOMENCLATURAL CHANGES IN THE BRYACEAE (BRYOPSIDA) FOR NORTH AMERICA II" (PDF). Phytologia. 89 (1): 110–114.