The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Thyme-mosses, etc.

In Dixon’s Bryaceae.

Gametophyte. Acrocarpous; somewhat dendroid (e.g., Plagiomnium undulatum), or not dendroid; forming tufts (commonly), or forming patches, or the plants scattered. Primary stems erect. Mature plants 3–100(–150) mm high. Plants without comal tufts (in contrast with many Bryaceae). Shoots complanate, or not complanate. Stems tomentose below, or not tomentose; with a differentiated central strand. The leaves elliptical to oblong, or ovate to narrowly lanceolate, or elliptical, or obovate (pellucid, the upper and lower leaves often quite different, but the former not apically crowded as in many Bryaceae. Epipterygium exhibits foliar dimorphism, with dorsal leaves smaller and narrower than the laterals, cf. Calomnion); spiral (mostly), or spiral to 3-ranked; crisped when dry, or not crisped when dry. Leaf bases decurrent to not decurrent. The leaves single-nerved. The leaf nerves extending beyond the middle of the leaf, but not to the tip, or extending to the leaf tip (commonly); excurrent (rarely), or not excurrent; incorporating stereids. Leaf blade apices obtuse, or pointed; apiculate (sometimes, e.g. in Plagiomnium and when emarginate in Rhizomnium), or not apiculate; apically rounded, or apically acute, or emarginate (sometimes in Rhizomnium). Leaf blade margins unistratose to several-stratose; denticulate to dentate (usually, the teeth single or double), or entire (e.g., Cinclidium). Leaf blades bordered (commonly), or not conspicuously bordered (e.g., Pseudobryum). The basal leaf cells more or less isodiametric; quadrate, or rectangular, or hexagonal, or rounded, or rhomboidal; smooth. The walls of basal leaf cells thin to thick; straight. The angular cells not well differentiated. The mid-leaf cells more or less isodiametric (especially in Mnium), or somewhat longitudinally elongated; quadrate, or rectangular, or hexagonal, or rounded, or rhomboidal; smooth. The walls of the mid-leaf cells thin (mostly), or thin to thick; straight.

Plants monoecious, or dioecious; when monoecious, synoecious. Plants gemmiferous (e.g., some Pohlia spp.), or not gemmiferous; the gemmae when present, in leaf axils and or on rhizoids.

Sporophyte. Capsules exserted; inclined to pendulous, or erect (more or less, in Mielichhoferia); symmetrical; straight (to very slightly asymmetrical?); sub-cylindric, or ellipsoid, or ovoid, or pyriform; with an externally conspicuous apophysis (those of Cinclidium with a distinct neck), or without an externally conspicuous apophysis; with an annulus. Calyptra symmetrical; splitting down one side. Capsules with a peristome. The peristome double (usually), or single (in Mielichhoferia, where the exostome is lacking, cf. Dicranideae). The peristome teeth 16; not deeply cleft; not perforated; thin, membranous, and transversely barred; when present, exteriorly with a fine longitudinal dividing line between the transverse bars. The inner peristome well developed (the outer being reduced in Mielichhoferia); about equalling the outer; with a basal membranous ring; with elongated “processes” (these keeled, often perforated). The processes of the inner peristome 16; alternating with the teeth of the outer peristome. The inner peristome ciliate. The operculum conical, or mamillate, or rostellate, or rostrate. Setae long; straight; often red or orange.

Ecology. Not associated with trunks of tree ferns.

Cytology. Haploid chromosome number, n = 6, 7, 12, 13, and 14.

British representation. 44 species. Cinclidium (Lurid Cupola-moss), Epipterygium (Tozer’s Thread-moss), Mielichhoferia (Copper-mosses), Mnium (Thyme-mosses), Pohlia (Thread-mosses), Plagiomnium (Thyme-mosses), Pseudobryum (River Thyme-moss), Rhizomnium (Thyme-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 Bryales.

Illustrations. • Mnium hornum (Curtis, 1824). • Epipterygium, Plagiobryum, Pohlia: Dixon. • Mielichhoferia and Pohlia spp. (with assorted other taxa): Dixon. • Plagiomnium (4 spp.) and 3 Mnium species: Dixon. • 5 Mnium species, and Pseudobryum cinclidioides: Dixon. • Cinclidium stygium and Rhizomnium punctatum: Dixon. • Cinclidium, Plagiomnium and Rhizomnium, with Amblyodon: Berkeley. • Epipterygium, (with Bryaceae): Dixon.

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.’.