The genus Bryum is a group of mosses that belongs to the Bryaceae family. Some common synonyms for Bryum include green moss, animal moss, and cat-mountain moss. These mosses typically grow in wet and moist environments, such as soil, rocks, and by streams. They are characterized by their fan-shaped leaflets that form dense clusters, which can easily trap and retain moisture. Other synonyms for Bryum that are closely related include Bryopsida, Bryinae, and Hypnobryales. Some varieties of Bryum species are considered invasive and can cause problems in certain environments. Despite this, Bryum remains a valuable component of many ecosystems, supporting a wide range of microfauna and flora.