2. Tetrodontium Schwägrichen, Sp. Musc. Frond. Suppl. 2(1,2): 102. 1824.
[Greek tetra, four, and odontos, tooth, alluding to peristome]
Plants very small, budlike, dull dark-green to brownish green, in scattered, gregarious or sometimes very small clumps. Thallose protonematal flaps persistent and usually present. Stems few, very short, less than 0.05 cm; flagelliform shoots may occur at the base of the stem, 0.2-0.5 cm, with 3-ranked, tightly appressed linear to lanceolate leaves. Leaves of main stem few, appressed, ovate, acuminate, or obtuse, margins entire or dentate, to 1.2 mm; costa single, weak or absent; laminal cells rhombic or rectangular. Specialized asexual structures absent. Sexual condition: perichaetial and perigonial buds occurring on the same protonema; perichaetial leaves ovate to ovate-lanceolate, concave. Seta 3-8 mm, straight, smooth, slightly twisted when dry. Capsule 0.6-1 mm, ovate to shortly oblong-cylindric, straight; operculum conic, obliquely apiculate; peristome usually not splitting or appearing to be more than four. Calyptra smooth or somewhat plicate, yellowish. Spores smooth or finely papillose, 10-16 µm.
Species 2 (2 in the flora): North America, South America (Chile); Eurasia, Pacific Islands (New Zealand).