3. Tetraplodon Bruch & Schimper, Bryol. Europ. 3: 211, plates 288-290. 1844. • [Greek tetraplo-, fourfold, and odon, tooth, alluding to arrangement of exostome teeth].
Plants in dense tufts, often brown proximally, bright green to yellow-green distally. Stems 0.5-3(-8) cm; often matted with rhizoids proximally. Stem leaves slender- to oblong-lanceolate, or obovate and acuminate; margins toothed or entire; apex acute, acuminate, or subulate; costa usually ending in subula; proximal laminal cells elongate, rectangular; distal cells rectangular, hexagonal, or oblong-hexagonal. Sexual condition autoicous or rarely dioicous. Seta 0.2-5 cm, not twisted. Capsule cleistocarpous or not, yellowish or reddish to dark brown or black, cylindric to ovoid or spindle-shaped; hypophysis same color or darker than urn, short to elongate, narrower to barely wider than urn; annulus usually absent; operculum hemispheric to bluntly conic; peristome single; exostome teeth 16, at first ± coherent in 4s, later in 2s, usually reflexed when dry, inflexed when moist, of 2 layers of cells. Calyptra conic-mitrate or cucullate, small, not constricted beyond base. Spores 8-12 µm, smooth or slightly papillose.
Species 10 (5 in the flora): nearly worldwide; alpine, subalpine, and temperate to subarctic regions.
Species of Tetraplodon are entomophilous and coprophilous although apparently restricted to the dung of carnivores, bones, and owl pellets.
SELECTED REFERENCE Steere, W. C. 1977b. Tetraplodon paradoxus and T. pallidus (Musci: Splachnaceae) in northern North America. Brittonia 29: 353-367.