The Moss Families of the British Isles


L. Watson and M. J. Dallwitz




Gametophyte. Plants “normal”, with leaves containing chlorophyll. Acrocarpous; cushion-forming (the cushions characteristically large, compact and rounded, glaucous or albescent). Mature plants 100–500 mm high. The leaves of main stems and branches similar in form (with a very peculiar and characteristic anatomical layout). The leaves leucobryoid (three or more layered, with a median, open network of long and narrow chlorophyllous cells, sandwiched between layers of much larger, empty, hyaline cells. The latter are interconnected by conspicuous pores, and some have openings to the outside, endowing the leaves with a sponge-like capacity to absorb and retain water. They are analogous in this respect with branch leaves of the unrelated Sphagnum, but lack the spiral wall thickenings characteristic of them). The leaves ovate to narrowly lanceolate; spiral; (sub-) secund (especially when moist), or not secund; crisped when dry, or not crisped when dry; at least theoretically, single-nerved (in that the greater part seems to represent nerve (cf. Polytrichum), the vestigial lamina being represented by its narrow margins). The leaf nerves extending to the leaf tip. Leaf blade apices pointed; acuminate; conspicuously hyaline, or not hyaline. Leaf blade margins entire. Leaf blades bordered. The basal leaf cells somewhat longitudinally elongated to longitudinally much elongated; rectangular; smooth. The walls of basal leaf cells thin; straight. The angular cells not well differentiated. The mid-leaf cells somewhat longitudinally elongated to longitudinally much elongated; rectangular (if the laminate component of the leaf is not regarded as entirely basal); smooth. The walls of the mid-leaf cells thin; straight.

Plants dioecious.

Sporophyte. Capsules exserted; erect to inclined; symmetrical to asymmetrical; weakly to strongly curved; clavate (slightly), or sub-cylindric to ellipsoid, or ovoid, or pyriform, or gibbous; with an externally conspicuous apophysis to without an externally conspicuous apophysis; striate and becoming regularly furrowed when dry and empty; dehiscing via a lid; with a peristome. The peristome single. The peristome teeth 16; not grouped; deeply cleft; perforated; thin, membranous, and transversely barred; interiorly exhibiting a fine longitudinal dividing line between the transverse bars. The operculum rostrate. Setae 8–18 mm long; straight, or curved.

Ecology. Occurring in acid conditions. On soil, rocks, tree stumps, in wet or dry locations, sometimes in bogs.

Cytology. Haploid chromosome number, n = 11 (in L. glaucum).

British representation. 2 species. Leucobryum. 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.

Illustrations. • Leucobryum juniperoideum and L. glaucum: Dixon. • Leucobryum (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.’.