Brachymenium is a mostly tropical/subtropical genus of about 70 species (Ochi 1992). Nearly all Brachymenium species have hexagonal to rhomboidal upper leaf cells, excurrent costae, and apiculate to hair-pointed leaves. Many of the common species also have quadrate basal leaf cells. The Brachymenium gametophyte has few distinct features, and sterile material can be difficult to distinguish from Bryum or Acidodontium. The Brachymenium sporophyte has erect to suberect capsules with conic-apiculate to short-beaked opercula. Its peristome is diplolepidous with narrow, densely papillose exostome teeth and reduced endostome. The Brachymenium endostome has a high or low basal membrane with the segments and cilia generally rudimentary to absent. When the segments and cilia are rudimentary, they are morphologically identical and as such the two structures can be identified only by their position relative to the exostome teeth. This endostome condition is often termed erose. A good example of the loss of segment/cilia differentiation in Brachymenium occurs in the bazaar endostome of  B. columbicum (De Not.) Broth. (see Shaw 1984). This endostome has a high basal membrane from which arise 16 morphologically similar, lanceolate structures. Each is positioned opposite an exostome tooth and represents a cilia/segment complex consisting of 4 fused parts: 2 cilia (in the center of the linear structure) with ½ of a segment on either side.

Brachymenium has been divided into five sections (see Ochi 1980, 1992) based on  features such as plant size, operculum shape, capsule shape and size, spore size, limbate condition of the leaves and peristome structure. The sections, however, have species with reticulating character combinations that serve as intermediates between the sections, making it sometimes difficult to separate them (Ochi 1980). Some of the present sectional characteristics may be of minor phylogenetic importance (e.g., plant and capsule size, present or absence of leaf border), and an analysis of the genus focusing on more reliable features (e.g., exostome and endostome morphology, spore size, basal leaf cell and lower costal ventral superficial cell shape) within the context of an in-depth character analysis for the Bryaceae is needed before a more natural subgeneric classification can be proposed.