The Moss Families of the British Isles

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L. Watson and M. J. Dallwitz

Helodiaceae

~ Thuidiaceae.

Gametophyte. Pleurocarpous; not dendroid; forming tufts. Primary stems procumbent (stoloniform, the secondary stems erect and pinnately branched). Paraphyllia present (abundant). The leaves of main stems and branches markedly different in form (those of the main stems broader and basally auriculate); bilaterally symmetrical; broadly ovate (to deltoid); longitudinally plicate. Leaf bases not sheathing; decurrent (Palustriella), or not decurrent. The leaves single-nerved. The leaf nerves extending beyond the middle of the leaf, but not to the tip. Leaf blade apices pointed; not apiculate; apically acute, or acuminate. Leaf blade margins revolute or recurved (below), or flat; unistratose; denticulate. Leaf blades not conspicuously bordered. The basal leaf cells somewhat longitudinally elongated to longitudinally much elongated; (uni-) papillose. The walls of basal leaf cells straight. The angular cells clearly differentiated (at least in the stem leaves, forming conspicuous auricles). The mid-leaf cells longitudinally much elongated; linear to vermicular (5 to 7 times as long as wide); papillose (the papillae mainly from the end-walls). The walls of the mid-leaf cells thick; straight.

Plants monoecious; autoecious.

Sporophyte. Capsules exserted; inclined to horizontal; asymmetrical; curved (arcuate); sub-cylindric; not waisted; neither flattened nor angular; with an externally conspicuous apophysis to without an externally conspicuous apophysis; smooth; with an annulus. Calyptra symmetrical; splitting down one side. Capsules with a peristome. The peristome double. The peristome teeth not basally joined; not grouped; not deeply cleft; not perforated; thin, membranous, and transversely barred (cross striolate); exteriorly with a fine longitudinal dividing line between the transverse bars. The inner peristome well developed; shorter than the outer; with a basal membranous ring; with elongated “processes”; ciliate. The operculum narrowly conical. Setae long; curved; red.

Ecology. In wet places; occurring in neutral pH conditions and acid conditions. In marshes and bogs.

Cytology. Haploid chromosome number, n = 12.

British representation. 4 species. Helodium (Tamarisk-moss), Palustriella (Hook-mosses). Southern Scotland and English Midlands (Helodium blandowii: recorded from Cheshire and Yorkshire, now seemingly extinct), or northern Scotland, southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, central southern England, southwest England, Isle of Wight, and Ireland (Palustriella).

Classification. Class Bryopsida; Subclass Bryideae; Order Hypnales.

Illustrations. • Palustriella, with Campyliaceae: Dixon. • Helodium blandowii, with 6 Thuidiaceae: Dixon. • Thuidium, with Anomodon and Helodium: 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’.

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