The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Hump-mosses, Silver-mosses, Thread-mosses, etc.

Excluding Mniaceae and Leptobryum.

Gametophyte. Plants “normal”, with leaves containing chlorophyll. Acrocarpous; forming tufts (mostly), or mat or turf forming, or forming patches, or growing through other Bryophytes. Primary stems usually erect. Mature plants when erect, about 2–120 mm high. Plants exhibiting comal tufts of leaves (often, by contrast with Mniaceae), or without comal tufts. Stems not tomentose. The leaves ovate to narrowly lanceolate, or narrowly lanceolate to linear; spiral; crisped when dry (occasionally, e.g. in some Bryum spp.), or not crisped when dry (usually, but commonly flexuose). Leaf bases decurrent (e.g., in some Bryum spp.), or not decurrent. The leaves single-nerved. The leaf nerves extending beyond the middle of the leaf, but not to the tip to extending to the leaf tip; excurrent, or not excurrent; incorporating stereids, or without stereids. Leaf blade apices conspicuously hyaline (Bryum capillare), or not hyaline. Leaf blade margins unistratose, or bi-stratose (Bryum p.p.). Leaf blades bordered (notably in species of Bryum), or not conspicuously bordered. The basal leaf cells longitudinally much elongated (mostly), or somewhat longitudinally elongated; more or less rhomboidal, or linear; smooth. The walls of basal leaf cells thin (mostly), or thick. The angular cells not well differentiated (for the most part), or clearly differentiated (sometimes to some extent, in comal leaves). The mid-leaf cells longitudinally much elongated (mostly), or somewhat longitudinally elongated; more or less rhomboidal (usually), or hexagonal, or linear, or linear to vermicular; smooth. The walls of the mid-leaf cells thin (mostly), or thick.

Plants monoecious, or dioecious; when monoecious, autoecious, or paroecious (commonly), or synoecious. Plants gemmiferous (e.g., Bryum erythrocarpum), or not gemmiferous; the gemmae when present, in leaf axils and or on rhizoids.

Sporophyte. Capsules exserted; inclined to pendulous; symmetrical (usually), or asymmetrical (Plagiobryum); straight, or straight to curved; sub-cylindric to ovoid (Mnium), or clavate, or pyriform (Bryum), or gibbous (Plagiobryum); with an externally conspicuous apophysis (e.g., in some Bryum species, Plagiobryum), or without an externally conspicuous apophysis; smooth. Calyptra large and covering the well-developed capsule, or small; symmetrical; splitting down one side. Capsules with a peristome. The peristome double. The peristome teeth 16; 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 to reduced; with a basal membranous ring (usually); usually with elongated “processes”. The processes of the inner peristome 16; alternating with the teeth of the outer peristome. The inner peristome ciliate, or without cilia. The operculum convex, or conical, or mamillate to subulate. Setae long; straight (usually), or curved (cygneous, in Plagiobryum), or flexuose.

Ecology. Occurring in basic habitats, or neutral pH conditions, or acid conditions (commonly). In diverse habitats, from low to high altitudes.

Cytology. Haploid chromosome number, n = 9, 10, 11, 20, 21, 22, 24, 27, 30, 33, and 40 (and occasionally with a supernumerary; many species of Bryum unrecorded).

British representation. About 60 species. Anomobryum (Silver-mosses), Bryum (Thread-mosses), Plagiobryum (Hump-mosses), Rhodobryum (Rose-moss). 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. • Anomobryum filiforme, and 10 Bryum species: Dixon. • 7 Bryum species: Dixon. • 8 Bryum species: Dixon. • 12 Bryum species, and Rhodobryum roseum: Dixon. • Plagiobryum and Rhodobryum (with assorted other taxa): 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.’.