The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Tufa-mosses, Screw-mosses, Crisp-mosses, Stubble-mosses, Pottias, etc.

Dixon’s Tortulaceae; excluding Cinclidotaceae (Cinclidotus).

Gametophyte. Always or nearly always acrocarpous (sometimes hygroscopic); cushion-forming, or forming tufts, or mat or turf forming, or forming patches, or the plants scattered. Rosette plants (often, more or less), or non-rosette plants. Mature plants 1–80(–120) mm high (but with numerous species reaching no more than about 2–3 mm, including Stegonia latifolia, which takes the form of tiny, stemless, bud-like plants). Plants exhibiting comal tufts of leaves (rarely), or without comal tufts. Shoots not complanate. Stems not tomentose; with a differentiated central strand, or without a differentiated central strand. The leaves neither sphagnoid nor leucobryoid. The leaves lingulate to obovate, or ovate, or lanceolate to linear (but generally ovate or spathulate, rarely narrow); spiral; not secund (almost invariably, though sometimes secund in Oxystegus tenuirostris); crisped when dry (commonly, e.g. in Tortula, Didymodon, Tortella, etc.), or not crisped when dry (e.g., Pottia). Leaf bases sheathing, or not sheathing. The leaves single-nerved. The leaf nerves extending to the leaf tip; excurrent (commonly, often conspicuously so), or not excurrent. Leaf blades adaxially longitudinally lamellate (with 4 lamellae, in species of Pottia and in Tortula Section Pterygoneurum), or not lamellate. Leaf blade apices obtuse, or pointed; apiculate, or not apiculate; apically rounded, or apically acute, or acuminate; conspicuously hyaline (commonly, via the excurrent nerve), or not hyaline. Leaf blade margins flat, or involute or incurved, or revolute or recurved; unistratose (usually), or bi-stratose (e.g., in the mid-section, in Trichostomopsis). Leaf blades bordered (notably in Tortula), or not conspicuously bordered. The basal leaf cells more or less isodiametric to somewhat longitudinally elongated, or longitudinally much elongated; rectangular, or rounded; papillose, or smooth. The walls of basal leaf cells usually thin (generally lax and hyaline), or thick (notably in Barbula); straight. The angular cells clearly differentiated, or not well differentiated. The mid-leaf cells more or less isodiametric, or more or less isodiametric to somewhat longitudinally elongated; quadrate, or rectangular, or hexagonal, or rounded; papillose (often), or smooth. The walls of the mid-leaf cells thin to thick; straight.

Plants monoecious, or dioecious (commonly or exclusively in some genera); when monoecious, autoecious (commonly), or paroecious, or synoecious (rarely). Plants gemmiferous (e.g., in some Tortula and Leptodontium), or not gemmiferous; the gemmae when present, borne on the leaf nerves and laminae.

Sporophyte. Capsules immersed (e.g., some Weissia and Phascum species, Acaulon), or emergent to exserted (sometimes slightly exserted in Phascum), or exserted; erect (usually), or erect to pendulous; symmetrical, or symmetrical to asymmetrical; straight (usually, more or less), or curved; globose (e.g., Pottia recta, Phascum spp.), or sub-cylindric, or ellipsoid (or obloid), or ovoid; without an externally conspicuous apophysis; smooth; with an annulus, or without an annulus. Calyptra symmetrical; splitting down one side, or with two or more splits. Capsules cleistocarpus (e.g., Weissia spp., Acaulon), or dehiscing via a lid; with a peristome, or without a peristome (in some Pottia species, Acaulon). The peristome single (often basally joined into a spirally twisted tube). The peristome teeth when present, 16, or 32; conspicuously spirally twisted (commonly), or not spirally twisted; joined basally to form a membranous ring, or not basally joined; deeply cleft, or not deeply cleft; not perforated, or perforated; thin, membranous, and transversely barred; when present and not cleft to the base into 32 teeth, interiorly exhibiting a fine longitudinal dividing line between the transverse bars. The operculum conical (e.g., Desmatodon), or rostellate to rostrate. Setae short to long; straight (usually), or straight to curved, or curved, or flexuose.

Ecology. Aquatic (Pleurochaete), or in wet places, or mesophytic, or xerophytic. Not saxicolous. In diverse habitats, but mostly terrestrial rather than rupestral.

Cytology. Haploid chromosome number, n = 11, 12, 13, 14, 15, 16, 20, 21, 24, 25, 26, 27, 28, 36, 40, 42, 48, 50, 52, 55, and 56 (etc.?, sometimes with supernumeraries, and numerous species not recorded).

British representation. About 110 species. Acaulon (Pygmy-mosses), Aloina (Aloe-mosses), Anoectangium (Summer-moss), Barbula (Bird’s-claw Beard-mosses), Bryoerythrophyllum (Beard-mosses), Dialytrichia (Pointed Lattice-moss), Didymodon (Beard-mosses), Eucladium (Whorled Tufa-moss), Gymnostomum (Tufa-mosses), Gyroweisia (Beardless- and Stubble-mosses), Hennediella, Hymenostylium (Tufa-mosses), Leptobarbula (Beric Beard-moss), Leptodontium (Beard- and Thatch-mosses), Leptophascum (Vectis-moss), Microbryum, Molendoa (Warburg’s Moss), Paraleptodontium (Drooping-leaved Beard-moss), Phascum (Earth-mosses), Pleurochaete (Side-fruited Crisp-moss), Pottia (Pottias), Pottiopsis (Pottias), Protobryum (Pottia), Pseudocrossidium (Beard-mosses), Pterygoneurum (Chalk-moss, Pottia), Scopelophila (Tongue-leaf Copper-moss), Stegonia (Hood-leaved Screw-moss), Syntrichia (Screw-mosses), Tortella Crisp-mosses), Tortula (Screw-mosses), Trichostomopsis, Trichostomum (Crisp-mosses), Weissia (Beardless- and Stubble-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 Dicranideae; Order Pottiales.

Comments. Thus circumscribed, an alarmingly diverse family which may be impossible to define satisfactorily.

Illustrations. • Acaulon, Phascum, Microbryum etc., with Hedwigiaceae: Dixon. • Tortula, Pottia, Pottiopsis, Pterygoneurum and Stegonia. • Aloina, Pterygoneurum and Tortula: Dixon. • 8 Tortula species: Dixon. • Bryoerythrophyllum, Didymodon and Syntrichia: Dixon. • Didymodon and Pseudocrossidium: Dixon. • Barbula (2 species), Leptodontium (2 species) and Weissia (9 species): Dixon. • 4 Tortella species, Anoectangium and Pleurochaete. • Dialytrichia, with Cinclidotus: Dixon. C. fontinaloides. D. mucronata. • Syntrichia, Pottia and Tortula, with Cinclidotus: Berkeley. • Tortula spp. and Hennediella: Berkeley. • Weissia controversa and W. squarrosa: Berkeley. • Tortula subulata: Curtis (1825).

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.’.