The Moss Families of the British Isles


L. Watson and M. J. Dallwitz



Gametophyte. Acrocarpous; forming tufts, or mat or turf forming. Primary stems usually erect. Mature plants 5–10 mm high. The leaves narrowly lanceolate to linear (the upper and lower leaves more or less similar, by contrast with Mniaceae); spiral. Leaf bases 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; not excurrent. Leaf blade apices acuminate; not hyaline. Leaf blade margins unistratose; obscurely denticulate, or entire. Leaf blades not conspicuously bordered. The basal leaf cells somewhat longitudinally elongated to longitudinally much elongated; rectangular; smooth. The walls of basal leaf cells straight. The angular cells not well differentiated. The mid-leaf cells longitudinally much elongated; rhomboidal to linear; smooth. The walls of the mid-leaf cells thin to thick; straight.

Plants monoecious; autoecious, or paroecious (O. gracile), or synoecious (or heteroecious). Parapyhyses absent. Plants not gemmiferous.

Sporophyte. Capsules exserted; more or less erect (O. gracile), or inclined to horizontal (O. lineare); symmetrical to asymmetrical; straight, or straight to curved; narrowly pyriform, or clavate; not waisted; neither flattened nor angular; without an externally conspicuous apophysis; smooth, or striate and becoming regularly furrowed when dry and empty. Calyptra large and covering the well-developed capsule; glabrous; symmetrical; splitting down one side. Capsules with a peristome. The peristome double. The peristome teeth 16 (these narrow, held erect); not basally joined; not grouped; not deeply cleft; not perforated; thin, membranous, and transversely barred; exteriorly with a fine longitudinal dividing line between the transverse bars. The inner peristome well developed; shorter than the outer to exceeding the outer; with a basal membranous ring (short), or without a basal membranous ring; with elongated “processes”. The processes of the inner peristome 16; alternating with the teeth of the outer peristome. The inner peristome without cilia. The operculum mamillate to rostrate. Setae long; flexuose (thin).

Ecology. Mesophytic; occurring in neutral pH conditions to acid conditions, or acid conditions (often on shaded sandstone rocks and rotting wood).

Cytology. Haploid chromosome number, n = 12, or 20 and 22.

British representation. 2 species. Orthodontium. Southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, central southern England, southwest England, Isle of Wight, and Ireland (O. lineare being common, and O. gracile widespread but rare).

Classification. Class Bryopsida; Subclass Bryideae; Order Bryales.

Illustrations. • Orthodontium gracile (with assorted other taxa): Dixon. • Orthodontium gracile (details, with Bryaceae and Meesiaceae): 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.’.