As noted by Andrews (1935) the Bryaceae seem to be “a very natural” group, but it is extremely large, variable, and numbingly complex. As a result it is nearly impossible to characterize. The family has a few genera (e.g., Epipterygium with complanate, dimorphic leaves) with odd gametophytes, but otherwise it typically has nondescript gametophytes with short, erect, acrocarpous stems, lanceolate to ovate, unicostate leaves that are generally acute, have bordered or unbordered margins, and relatively long leaf cells. Peristome development within the family is also remarkably variable, ranging from genera (e.g., Rhodobryum) having perhaps the most perfectly developed diplolepidous peristome in the mosses through every conceivable type of exostome and/or endostome reduction to absent. Andrews (1935) suggested the family might best be understood as a “single large natural genus (Bryum)” and in this regard it is noteworthy that Ochi, based on long, world-wide experience with its variability and species, consistently took a broad generic view of the family.

Genera and species within the Bryaceae are often based on sporophytic characters and as a result taxonomic problems in the family can be overwhelming (Crum & Anderson 1981). Sterile material sometimes cannot be determined even to genus without extensive prior experience with the family. Likewise, identification at the species level at times requires good sporophytic material.