The Moss Families of the British Isles

DELTA Home

L. Watson and M. J. Dallwitz

Plagiotheciaceae

Silk-mosses.

~Hypnaceae; sensu stricto, excluding Herzogiella, Isopterygiopsis, Isopterygium, Myurella, Orthothecium, Platydicta, Pseudotaxiphyllum, and Taxiphyllum.

Gametophyte. Pleurocarpous; forming patches. Shoots nearly always more or less complanate (and/or secund, but sometimes not consistently so, and no more than sub-complanate in P. cavifolium). Paraphyllia absent. Pseudoparaphyllia absent (if the family is confined to Plagiothecium, with Taxiphyllum excluded). Stems with a differentiated central strand (this small but distinct). The leaves of main stems and branches usually similar in form; bilaterally symmetrical to markedly asymmetrical; ovate to lanceolate; spiral; secund, or not secund. Leaf bases decurrent (if the family is confined to Plagiothecium). The leaves double-nerved, or nerveless (rarely). The leaf nerves when present, not extending beyond the middle of the leaf, or extending beyond the middle of the leaf, but not to the tip. Leaf blade apices pointed; apically acute, or acuminate. Leaf blade margins flat, or revolute or recurved; entire to dentate. Leaf blades bordered, or not conspicuously bordered. The basal leaf cells longitudinally much elongated; rhomboidal, or linear to vermicular; smooth. The walls of basal leaf cells thin to thick; straight. The angular cells clearly differentiated (commonly enlarged), or not well differentiated. The mid-leaf cells longitudinally much elongated; narrowly rhomboidal, or linear to vermicular; smooth. The walls of the mid-leaf cells thin to thick; straight.

Plants monoecious, or dioecious; when monoecious, autoecious.

Sporophyte. Capsules exserted; erect to inclined, or horizontal; symmetrical to asymmetrical; straight to curved; sub-cylindric to ellipsoid, or pyriform; with an externally conspicuous apophysis to without an externally conspicuous apophysis. The apophysis becoming conspicuously rugose and/or twisted, or remaining smooth. Capsules smooth, or striate and becoming regularly furrowed when dry and empty; with an annulus (2–3 seriate, sometimes deciduous). Calyptra symmetrical; splitting down one side. Capsules with a peristome. The peristome double. The peristome teeth 16 (cross-striate below); 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; with a basal membranous ring, or without a basal membranous ring; with elongated “processes”. The processes of the inner peristome 16 (these keeled and perforated); alternating with the teeth of the outer peristome. The inner peristome ciliate, or without cilia. The operculum conical to rostrate. Setae long; straight; usually reddish; smooth.

Ecology. In diverse habitats, from low altitude swamps and marshes to rock ledges at high altitudes.

Cytology. Haploid chromosome number, n = 7, 8, 10, 11, 12, 20, and 25 (sometimes with one or two supernumeraries).

British representation. 10 species (on the sensu stricto interpretation). Plagiothecium. 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 Bryideae; Order Hypnales.

Comments. This following Ochyra and O’Shea (2004) in retaining Plagiothecium as a monotypic family, and returning other genera formerly included to Hypnaceae.

Illustrations. • Plagiothecium: piliferum, with Hypnaceae Dixon. • Plagiothecium (4 species), with Herzogiella striatella: Dixon. • Plagiothecium, with Brachytheciaceae and Hypnaceae: 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. http://delta-intkey.com’.

Contents