The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Bristle-, Pincushion- and Yoke-mosses.

Excluding Amphidium.

Gametophyte. Really acrocarpous, or pleurocarpous (or rather, sometimes ostensibly so, because of branching from beneath the perichaetium); cushion-forming (the leaves usually conspicuously hygroscopic). Mature plants 2–80 mm high. Stems tomentose below, or not tomentose. The leaves neither sphagnoid nor leucobryoid. The leaves ovate to narrowly lanceolate, or linear, or lingulate; spiral; crisped when dry (usually, in Zygodon and Ulota), or not crisped when dry (Orthotrichum); single-nerved. The leaf nerves extending beyond the middle of the leaf, but not to the tip, or extending to the leaf tip; excurrent, or not excurrent. Leaf blade apices obtuse (sometimes), or pointed (usually); apiculate, or not apiculate; apically rounded (occasionally), or apically acute, or acuminate; conspicuously hyaline (Orthotrichum diaphanum), or not hyaline. Leaf blade margins flat, or involute or incurved, or revolute or recurved. Leaf blades not conspicuously bordered. The basal leaf cells somewhat longitudinally elongated, or longitudinally much elongated; rounded, or rhomboidal, or linear; papillose, or smooth. The walls of basal leaf cells thin, or thick; straight. The angular cells not well differentiated. The mid-leaf cells more or less isodiametric; hexagonal to rounded; papillose, or smooth. The walls of the mid-leaf cells thin to thick; straight.

Plants monoecious, or dioecious; when monoecious, autoecious. Plants gemmiferous (e.g., species of Ulota and Orthotricum), or not gemmiferous; the gemmae when present, clustered towards the tips of excurrent leaf nerves (Ulota phyllantha), or borne on the leaf nerves and laminae (Orthotrichum lyelli).

Sporophyte. Capsules immersed to exserted (variable in Zygodon and Orthotrichum, but usually more or less immersed), or exserted (Ulota); erect; straight; more or less ellipsoid (though often long necked); striate and becoming regularly furrowed when dry and empty (8 striae in Ulota and Zygodon, 8 or 16 in Orthotrichum). Calyptra large and covering the well-developed capsule; glabrous (often, with coarse erect hairs), or hairy; symmetrical; plicate (often), or not plicate; splitting down one side, or with two or more splits. Capsules with a peristome (usually, sometimes vestigial), or without a peristome (e.g., some Zygodon species). The peristome when present, usually double, or single (e.g., in some Ulota species, where the endostome can be rudimentary or lacking). The peristome teeth when present, 8 (by fusion of pairs), or 16; not grouped, or in pairs (commonly); not perforated, or perforated; thin, membranous, and transversely barred; when present, exteriorly with a fine longitudinal dividing line between the transverse bars. The inner peristome shorter than the outer to about equalling the outer; with elongated “processes”, or without “processes” (when present, thinner than the outer peristome). The processes of the inner peristome when present, e.g. in Ulota, Orthotrichium 8, or 16; when present, alternating with the teeth of the outer peristome. The operculum rostellate, or rostrate. Setae very short to long; straight.

Ecology. Mainly growing on rocks or bark.

Cytology. Haploid chromosome number, n = 6, or 10 (+1), or 11, or 12.

British representation. 32 species. Orthotrichum (Bristle-mosses), Ulota (Pincushion-mosses), Zygodon (Yoke-mosses). 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 Bryopsida; Subclass Bryideae; Order Orthotrichales.

Illustrations. • Zygodon, with Amphidium: Dixon. • Orthotrichum, Ulota, Zygodon: Dixon. • 8 Orthotrichum species: Dixon. • 4 Orthotrichum species: Dixon. • Orthotrichum and Zygodon, with Amphidium: 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.’.