The small plants and cleistocarpic, pyriform capsules are distinctive and are diagnostic for the genus. Vegetatively the two Southern African species are very similar, although B. brevipes is slightly larger. The spores offer the only reliable characters for separating the species.
Plants minute, gregarious, light green; terricolous. Stems erect, to 0.5 mm high; in section with small central strand, cortical cells in ± 3 rows, uniform in size, incrassate, reddish. Leaves erect, bistratose above base; oval to ovate, acuminate to subulate in sub-perichaetial leaves, 1-2 mm long; margins plane, entire to serrulate by projecting cells. Costa excurrent, awn of upper leaves serrulate; ventral and dorsal superficial cells elongate, frequently prorate; in section guide cells 4, central, ventral cells in one layer, large, dorsal cells in 2 layers, large, incrassate. Laminal cells narrowly rectangular above shoulders; basal cells broader, rectangular to oblong-hexagonal. Autoicous. Perigonia axillary, leaves oval-acuminate, 0.8 mm long. Perichaetial leaves oval-subulate, 2.5 mm long. Seta erect, 0.3-0.4 mm long; capsule cleistocarpic, pyriform, to 1 mm long, neck with numerous stomata, to 0.5 mm long; calyptra mitriform, covering upper urn; spores rounded to subreniform, spinose, 40-45 µm, yellowish.