The mosses in this class are known as the true mosses and are represented by over 650 genera and 9,000 species worldwide. This group is differentiated from the other two classes of moss by the "lid" of the spore capsule, which is composed of a concentric series of "teeth". As the spore capsule dries out, the teeth bend upwards and allow the spores to be released. True mosses are abundant in the Arctic and may be found in almost any habitat, except the ocean.
Examples of this group in the Arctic include:
Bryum argentum: This species can be found on moist soil, brick, cement, and dozens of other surfaces. It tends to prefer disturbed areas and can be found on exposed surfaces, as well as enriched areas (e.g., bird roosts). This moss is a cosmopolitan species it is found on every continent (including Antarctica), in almost every habitat, and at all altitudes!
Bryum argentum often grows on rock.
A close-up of the reproductive structures of Bryum argentum.