Sphagnum mosses are the dominant feature of peat bog vegetation. They have specific characteristics that allow them to play a major role in the formation and sustainability of these ecosystems. Sphagnum mosses contribute directly to maintain water-logged conditions in peatlands because of their ability to retain water, especially for hummock-forming species. They play a role in the acidification process by releasing humic acid and are efficient at absorbing and keeping nutrients. All these characteristics favour Sphagnum growth and make them harsh competitors against other plant species. They also give Sphagnum peat its characteristic structure that make it a valuable product, especially for horticultural uses.
The structure of Sphagnum mosses is composed of a capitulum (head) made by the concentration of young branches at the top. This is where the growth occurs from the apical bud. Hanging branches disposed along the stem and covered by imbricated leaves are responsible for the capillary water supply. Stems have leaves (caulinary leaves) of different shapes, which are used in identification of species.