Tetrodontium Schwagrichen, Spec. Musc. Frond., Suppl. Primum. 2(1): 102. 1824.
[Greek tetra, four, odont, teeth]
Plants very small, budlike, dull dark-green to brownish green, in scattered, gregarious or sometimes very small clumps. 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 three-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 lacking. 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, varieties 2 (2 species, 2 varieties in the flora): rare, widely scattered in the northern Hemisphere, North America, suboceanic Temperate Zone, disjunctive to South America (Chile) and southern Pacific Islands (New Zealand).
Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern North America. 2 vols. New York. Ireland, R. 1982. Moss Flora of the Maritime Provinces. National Museums of Canada. Publications in Botany 13. Ottawa, Canada. Murray, B. M. 1987. Andreaeaobryeaceae--Tetraphidaceae. In: E. Nyholm. 1987. Illustrated Moss Flora of Arctic North America and Greenland. Vol. 3. Pp. 651--655. Stockholm.