The Bartramiaceae exhibit considerable gametophytic and sporophytic variation, yet the family is held together by a number of fairly constant and distinctive features. The leaves throughout the family tend to be narrow and often the leaf base is differentiated. Leaf cells in the family tend to be sharply angled, narrow, and strongly papillose or prorulose. Over all, leaf marginal serration in the Bartramiaceae is variable and two major types can be found. In one the leaf margins have two rows of teeth, in the other the marginal leaf cells have both cell ends projecting as mammillae with contiguous cells having the mammillae more or less fused. In a confusing way these two types of marginal serrations are both called doubly serrate. In the following treatment the term doubly serrate is used for two rows of teeth while the term jugate (suggested by Norton Miller, pers. comm.) is used for the more or less fused mammillae on contiguous marginal cells.

Sporophytically, its mostly globose and strongly furrowed capsules are critical features of the family, but more importantly the Bartramiaceae have a remarkable endostome which tightly binds the family. In those members of the family with a well-developed endostome the segments are broad and when examined with a hand-lens appear to be positioned opposite to rather than alternating with the exostome teeth. Closer examination reveals each segment is split along the median line nearly to the basal membrane and each half segment diverges outward toward the cilia where they often meet the diverging half segment of the next segment over, thus framing the cilia. This endostome structure is sometimes simply noted in the literature as “cilia cohering” (Zales 1973); however, Herzog (1916, Fig. 35e) provided an excellent illustration, and Shaw and Rohrer (1984) correctly evaluated the structure. Within the Bartramiaceae this type of endostome is found in Bartramia, Breutelia, Philonotis and Plagiopus. Curiously, a similar endostomial modification is found in the Bryaceae (Acidodontium and Brachymenium columbicum). Lastly, the Bartramiaceae tend to have large, densely ornamented, reniform spores.

Griffin and Buck (1989) discussed the intrageneric relationships of the Bartramiaceae and gave a subfamily classification based primarily on axillary hair morphology. The following key is intended only for the Central American genera of the Bartramiaceae.