In mosses (Bryophyta), the peristome is a structure made up of articulated teeth that allow spores to be dispersed through hygroscopic movements. Due to their high variability, the shape and structure of the peristome have often been used as a criteria in taxonomic classifications. The Pottiaceae is a highly diverse family, comprising around 1255 species with a worldwide distribution. The taxonomy of the Pottiaceae is known to be difficult partly due to the small size of the plants and high variability of gametophyte characters. Pottiaceae have a peristome consisting of a single row of teeth, generally described as a ‘pottioid peristome' composed of 16 teeth that divide into 32 twisting filaments. The aim of this study is to investigate the architecture of the mature peristome of nine species belonging to two subfamilies of Pottiaceae, through structural and anatomical observations, to understand peristome behaviour and movement, as well as the features that characterise the different peristomes. The shape, structure and hygroscopic behaviour of the peristome in the nine species were documented and photographed under dry and wet conditions. The internal anatomy of the area where the peristome teeth are inserted into the capsule and the teeth themselves were studied using histological techniques. These sections were prepared following the recently developed protocol that is specifically employed for peristomes sampled from specimens in herbaria, which consists of embedding the peristomes in Technovit® 7100 resin and sectioning them with a microtome before staining and mounting the preparation for observation under a microscope. A total of 303 photographs were taken from 65 capsules from 21 different specimens of the nine species of Pottiaceae. This study documented the structure of the peristome and concluded that it exhibits xerochastic behaviour in all nine species studied, i.e. it opens in dry conditions and closes in wet conditions, which support earlier observations in the literature. Histological analysis revealed common characteristics as well as variability among species in terms of the cellular organisation of the tooth insertion region and the structure and ornamentation of the teeth. The analysis distinguished two types of peristomes: those that conform to the definition of a ‘pottioid peristome’, with teeth that divide into spiral filaments, and others with short, entire teeth, which deviate from this definition. These observations highlight the diversity of peristomes within the Pottiaceae and question, among other things, the application of the term ‘pottioid peristome’, underscoring the need to explore the peristome further and redefine the peristome type in this family.