Plants of acidic rock, often volcanic, brownish. Alar cells not differentiated. Perigonial leaves broader and shorter than vegetative leaves. Perichaetial leaves similar to vegetative leaves. Sexual condition autoicous or rarely dioicous. Capsule striate; annulus compound; peristome teeth papillose or absent. Calyptra mitrate to sometimes sub-cucullate. Brachydontium is a genus of tiny, brownish plants of acidic rocks with striate capsules and peristomes ranging from well developed to completely absent. The species in the flora are olive green to brownish, stems ca. 0.6-2 mm; leaves 0.5-2.5 mm, erect, in ± two apparent rows, lanceolate-subulate, obtuse, leaf margins nearly entire, costa filling the subula; and the columella is not developed. They grow sympatrically on Mt. Rainier.