Brachydontium is a genus of minute, acrocarpous mosses found throughout the world. The genus is predominately autoicous (B. curvisetum Crum is dioicous). It has strongly costate leaves, smooth, firm-walled leaf cells and undifferentiated alar cells. It is separated from other gametophytically similar mosses (except Campylostelium) by its mitrate calyptra. Also distinctive are its shortly truncate, papillose peristome teeth that barely exceed a large, compound annulus. The setae in most species are cygneous.