2. Tetrodontium Schwaegr. 小四齿藓属 xiao si-chi xian shu
Sp. Musc. Frond., Suppl. 1, 2(1): 102. 1824.
Plants minute, budlike, dark green or brownish, gregarious or in scattered clumps. Stems very short, erect, simple or branched at base, with a few scale-like leaves and rhizoids at base. Protonematal flaps present or lacking. Leaves erect, crowded on short stems, obscurely in 3 ranks, narrowly ovate to oblong-ovate or oblong-lanceolate, somewhat concave, bluntly acute or acuminate at apex; margins entire or irregularly serrulate near the apex; costa very slender, weak, ending well below leaf apex or sometimes absent; upper and median leaf cells irregularly rhomboidal or irregularly hexagonal, firm, smooth; lower cells narrowly rectangular. Autoicous. Setae elongate, straight or slightly curved, smooth; capsules oblong-ovoid to shortly cylindrical, erect, symmetric, dark brownish, smooth; stomata few on the neck; opercula low-conic; annuli absent; peristome teeth 4, narrowly to broadly triangular, deeply inserted below the mouth. Calyptrae long-conic, covering most of the urns, naked, deeply split. Spores spherical, smooth.