The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Four-tooth Mosses.

Gametophyte. Acrocarpous; forming tufts, or forming patches, or gregarious. Rosette plants (Tetrodontium), or non-rosette plants. Mature plants to 2–15(–35) mm high. Stems with a differentiated central strand (?), or without a differentiated central strand (Tetradontium). The leaves orbicular to ovate, or lanceolate; spiral; nerveless, or single-nerved (mostly). The leaf nerves when present, extending beyond the middle of the leaf, but not to the tip. Leaf blade apices pointed; apically acute, or acuminate. Leaf blade margins entire. The basal leaf cells more or less isodiametric to somewhat longitudinally elongated, or longitudinally much elongated; rectangular to rounded; smooth. The walls of basal leaf cells thick; straight. The angular cells not well differentiated. The mid-leaf cells more or less isodiametric to somewhat longitudinally elongated; rectangular to rounded, or linear; smooth. The walls of the mid-leaf cells thick; straight.

Plants monoecious; autoecious (usually), or synoecious. Plants gemmiferous (in T. pellucida only); the gemmae of T. pellucida in leaf axils and or on rhizoids.

Sporophyte. Capsules exserted; erect; symmetrical; elongate; straight; sub-cylindric to ovoid; without an externally conspicuous apophysis; smooth; without an annulus. Calyptra symmetrical; plicate (Tetraphis), or not plicate; with two or more splits. Capsules with a peristome (the teeth retaining a cellular structure, and in this respect contrasting with conventional moss peristomes, where these comprise only the thickened parts of cell walls remaining after the rest of the cells have degenerated; cf. only the Polytrichaceae). The peristome ostensibly single. The peristome teeth 4; not basally joined; not deeply cleft; not perforated; solid, without transverse bars (derived from several concentric series of sporogonium cells). The processes of the inner peristome opposite the teeth of the outer peristome. The operculum conical. Setae 4–15 mm long; straight.

Ecology. Occurring in acid conditions, or neutral pH conditions and acid conditions. Tetraphis on rotting wood, peat and sandstone rocks, Tetradontium associated with acidic rocks in heavy shade by streams and rivers.

Cytology. Haploid chromosome number, n = 6, 7, and 8.

British representation. 3 species. Tetraphis, Tetrodontium. Northern Scotland, southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, central southern England, southwest England, Isle of Wight, and Ireland.

Classification. Class Polytrichopsida; Order Tetraphidales.

Illustrations. • Tetraphis pellucida and Tetradontium brownianum: Dixon. • Tetraphis pellucida: Berkeley.

To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The moss families of the British Isles. Version: 21st June 2009.’.