The peristome is considered to be the most complex and conservative morphological structure in the mosses. The arthrodontous peristome is composed of a single, or double, ring of teeth that surrounds the capsule’s opening in the peristomate mosses. Peristome features have long been used for classification at the higher taxonomic ranks and its structural complexity makes it a powerful criterion for unraveling evolutionary events across the mosses. In the monophyletic Dicranidae, a group that contains a third of total moss diversity, the peristome is haplolepidous with a single ring of teeth. In this thesis, the combination of anatomy and morphology allowed for a global comparison of peristomes in and across the Dicranidae. New diagnostic features for peristome pattern identification have been found and the taxonomic importance of the peristome at lower taxonomic ranks has been confirmed in the Dicranidae.