The Moss Families of the British Isles


L. Watson and M. J. Dallwitz


Excluding Daltoniaceae, Pilotrichaceae.

Gametophyte. Pleurocarpous; forming patches (these succulent). Primary stems procumbent (stems scarcely or sparsely branched). Mature plants with shoots to 60 mm long in H. lucens, to 35 mm in Achrophyllum dentatum. Shoots complanate. The leaves bilaterally symmetrical, or bilaterally symmetrical to markedly asymmetrical; ovate, or obovate; spiral; nerveless (Hookeria), or double-nerved to single-nerved (the nerve often forked, in Achrophyllum). The leaf nerves in Achrophyllum, not extending beyond the middle of the leaf (reaching to only about a third). Leaf blade apices obtuse, or obtuse to pointed; not apiculate; apically rounded, or apically acute. Leaf blade margins flat; unistratose; entire (Hookeria), or denticulate to dentate (Achrophyllum). Leaf blades not conspicuously bordered. The basal leaf cells somewhat longitudinally elongated; irregularly to elongate hexagonal; smooth. The walls of basal leaf cells thin; straight. The angular cells not well differentiated. The mid-leaf cells somewhat longitudinally elongated; irregularly hexagonal to rhomboidal; smooth. The walls of the mid-leaf cells thin; straight.

Plants monoecious.

Sporophyte. Capsules exserted; horizontal, or horizontal to pendulous; symmetrical; straight; ellipsoid, or ovoid; not waisted; neither flattened nor angular; without an externally conspicuous apophysis. Calyptra symmetrical; with two or more splits (mitriform). Capsules with a peristome. The peristome double. The peristome teeth 16; not basally joined; 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; about equalling the outer; with a basal membranous ring (this high); with elongated “processes” (these keeled). The processes of the inner peristome 16; alternating with the teeth of the outer peristome. The inner peristome ciliate, or without cilia. The operculum rostrate. Setae about 2 cm long, stout; straight; smooth, or rough.

Ecology. In wet places, or mesophytic. On damp, shaded soil.

Cytology. Haploid chromosome number, n = 6 and 9.

British representation. 2 species. Achrophyllum (Clear-leaf Moss), Hookeria (Hookeria). Northern Scotland, southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, central southern England, southwest England, Isle of Wight, and Ireland (H. lucens widespread and common), or southwest England (Achrophyllum dentatum in Cornwall probably having been introduced with Australia tree ferns).

Classification. Class Bryopsida; Subclass Bryideae; Order Hookeriales.

Illustrations. • Hookeria lucens, with Cyclodictyon and Daltonia: Dixon. Daltonia splachnoides. Cyclodictyon laetevirens. Hookeria lucens. • Hookeria, with Daltonia, Fontinalaceae, etc.: 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.’.