The Moss Families of the British Isles


L. Watson and M. J. Dallwitz



Gametophyte. Acrocarpous; cushion-forming, or forming tufts, or forming patches, or the plants scattered. Non-rosette plants. Mature plants 1–120(–150) mm high (but mostly small plants, usually with unbranched stems). Shoots complanate, or not complanate. Stems not tomentose; with a differentiated central strand. The leaves neither sphagnoid nor leucobryoid. The leaves more or less lanceolate (usually, the upper often longer than the lower), or subulate (sometimes comprising mainly nerve); distichous (Distichium), or not distichous; when not distichous, spiral; more or less secund, or not secund; crisped when dry (rarely), or not crisped when dry; single-nerved. The leaf nerves extending beyond the middle of the leaf, but not to the tip to extending to the leaf tip; excurrent to not excurrent (sometimes percurrent); incorporating stereids (these in two bands). Leaf blade apices apically acute, or acuminate; conspicuously hyaline (?), or not hyaline. Leaf blade margins flat, or involute or incurved, or revolute or recurved. Leaf blades not conspicuously bordered. The basal leaf cells somewhat longitudinally elongated to longitudinally much elongated; rectangular to linear; smooth. The walls of basal leaf cells straight. The angular cells not well differentiated. The mid-leaf cells more or less isodiametric to longitudinally much elongated; quadrate to linear; smooth. The walls of the mid-leaf cells thin to thick; straight.

Plants monoecious, or dioecious (most Ditrichum species); when monoecious, autoecious, or paroecious, or synoecious.

Sporophyte. Capsules immersed (Pseudephemerum), or immersed to emergent (e.g., in Pleuridium), or exserted; erect, or inclined; symmetrical, or asymmetrical; straight, or curved; globose, or sub-cylindric, or ellipsoid, or ovoid, or gibbous; with an externally conspicuous apophysis, or without an externally conspicuous apophysis; smooth, or striate and becoming regularly furrowed when dry and empty; with an annulus, or without an annulus. Calyptra symmetrical; splitting down one side, or with two or more splits. Capsules cleistocarpus (Pleuridium, Pseudephemerum), or dehiscing via a lid; with a peristome, or without a peristome (when cleistocarpus). The peristome when present single. The peristome teeth when present, 16; not grouped; deeply cleft (often almost to the base, into 32 divisions), or not deeply cleft; not perforated, or perforated; thin, membranous, and transversely barred; when present, interiorly exhibiting a fine longitudinal dividing line between the transverse bars; terete, filiform and smooth, or smooth below and papillose above. The operculum when present, conical to rostrate, or subulate (the cleistocarpous capsule of Pleuridium with a blunt apiculus, that of Pseudephemerum beaked). Setae short to long; straight, or curved.

Ecology. In diverse habitats.

Cytology. Haploid chromosome number, n = 12, 13, 14, 24, 26, and 28 (rarely with a supernumerary).

British representation. 19 species. Ceratodon (Redshank Mosses), Cheilothela (Rabbit Moss), Distichium (Distichiums), Ditrichum (Ditrichums and Path-moss), Pleuridium (Earth-mosses), Pseudephemerum (Delicate Earth-moss, which seems to fit better here than in Dicranaceae, to which it is commonly referred), Saelania (Dew-moss), Trichodon (Cylindric Ditrichum). 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 Dicranales.

Comments. The upper leaves usually longer than the lower leaves.

Illustrations. • Distichium, Ditrichum and Pleuridium, with Seligeriaceae. • Ceratodon and Saelania (with Rhabdoweisiaceae and Seligeriaceae: Dixon. • Pseudephemerum and Pleuridium: Dixon. Pleuridium acuminatum. Pseudephemerum nitidum. • Distichium capillaceum and Ditrichum heteromallum: Berkeley. • Ceratodon (with assorted dicranoid 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.’.