The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Grimmias, Fringe-mosses, etc.

Excluding Ptychomitriaceae and Hedwigiaceae.

Gametophyte. Acrocarpous, or cladocarpous (the plants often dark green or blackish); mostly cushion-forming, or forming tufts (the leaves usually conspicuously hygroscopic). Mature plants when tufted, to about 3–30(–100) mm high. The leaves distally subulate, or ovate to linear (commonly narrow); not crisped when dry (except in three species of Grimmia Section Rhabdogrimmia); 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 (but then often percurrent). Leaf blade apices obtuse (rarely), or pointed; apically rounded (rarely), or apically acute, or acuminate; conspicuously hyaline (commonly, the hyaline point being laminar, rather than representing an excurrent nerve - in contrast with that of Pottiaceae), or not hyaline. Leaf blade margins unistratose to several-stratose; entire (usually), or denticulate to dentate (distally, sometimes bluntly toothed near the apex, or crenulate). The basal leaf cells somewhat longitudinally elongated to longitudinally much elongated; quadrate, or rectangular, or linear; papillose, or smooth. The walls of basal leaf cells thin, or thick; straight, or sinuous (often). The angular cells not well differentiated (usually), or clearly differentiated (sometimes, in Racomitrium). The mid-leaf cells more or less isodiametric (overwhelmingly), or longitudinally much elongated; usually mostly quadrate, or rectangular, or rounded; papillose, or smooth. The walls of the mid-leaf cells thick; sinuous (mostly), or straight (e.g., in Coscinodon).

Plants monoecious, or dioecious (often); when monoecious, autoecious.

Sporophyte. Capsules immersed to emergent (in some Grimmia species), or exserted; erect to pendulous; somewhat asymmetrical (rarely), or symmetrical (nearly always); when more or less elongated, straight; globose, or sub-cylindric to ovoid (mostly), or clavate, or pyriform, or gibbous (e.g., Grimmia crinita); without an externally conspicuous apophysis; smooth (mostly), or striate and becoming regularly furrowed when dry and empty (e.g., in Grimmia pulvinata and G. orbicularis). Calyptra symmetrical; plicate (Coscinodon), or not plicate; splitting down one side, or with two or more splits. Capsules with a peristome. The peristome single. The peristome teeth 16; not basally joined; not deeply cleft (then cleft only at the tips, or entire), or deeply cleft (sometimes, in Racomitrium); not perforated, or perforated; thin, membranous, and transversely barred; without longitudinal dividing lines (the peristome otherwise similar to that of Dicranales, but less regularly cleft). The operculum conical, or rostellate, or rostrate, or subulate. Setae long or short; curved, or straight (in some species of Section Eu-grimmia).

Ecology. Variously in wet places to xerophytic; occurring in basic habitats, neutral pH conditions, and acid conditions. Mostly saxicolous, the species of Grimmia almost exclusively so, often montane.

Cytology. Haploid chromosome number, n = 12, 13, 14, 22, and 26.

British representation. About 60 species. Coscinodon (Sieve-tooth Moss), Dryptodon (~Grimmia), Grimmia (Grimmias), Racomitrium (Fringe-mosses), Schistidium (Grimmias). 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 Dicranideae; Order Grimmiales.

Illustrations. • 11 Grimmia species: Dixon. • 9 Grimmia species and Dryptodon patens: Dixon. • 6 Grimmia and 4 Racomitrium species, Schistidium apocarpum: Dixon. • Schistidium acrocarpum, Schistidium maritimum and Grimmia anodon: Dixon. • 5 Racomitrium species, and Coscinodon cribrosus: Dixon. • Grimmiaceae, Hedwigiaceae, Ptychomitriaceae: 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.’.