|
| The moss families (Bryophyta, Musci) of Britain and Ireland |
Thread-mosses.
Gametophyte. Acrocarpous; forming tufts, or mat or turf forming. Primary stems usually erect. Mature plants 5–10 mm high. The leaves narrowly lanceolate to linear (the upper and lower leaves more or less similar, by contrast with Mniaceae); spiral. Leaf bases decurrent. The leaves single-nerved. The leaf nerves extending beyond the middle of the leaf, but not to the tip, or extending to the leaf tip; not excurrent. Leaf blade apices acuminate; not hyaline. Leaf blade margins unistratose; obscurely denticulate, or entire. Leaf blades not conspicuously bordered. The basal leaf cells somewhat longitudinally elongated to longitudinally much elongated; rectangular; smooth. The walls of basal leaf cells straight. The angular cells not well differentiated. The mid-leaf cells longitudinally much elongated; rhomboidal to linear; smooth. The walls of the mid-leaf cells thin to thick; straight.
Plants monoecious; autoecious, or paroecious (O. gracile), or synoecious (or heteroecious). Parapyhyses absent. Plants not gemmiferous.
Sporophyte. Capsules exserted; more or less erect (O. gracile), or inclined to horizontal (O. lineare); symmetrical to asymmetrical; straight, or straight to curved; narrowly pyriform, or clavate; not waisted; neither flattened nor angular; without an externally conspicuous apophysis; smooth, or striate and becoming regularly furrowed when dry and empty. Calyptra large and covering the well-developed capsule; glabrous; symmetrical; splitting down one side. Capsules with a peristome. The peristome double. The peristome teeth 16 (these narrow, held erect); 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; shorter than the outer to exceeding the outer; with a basal membranous ring (short), or without a basal membranous ring; with elongated “processes”. The processes of the inner peristome 16; alternating with the teeth of the outer peristome. The inner peristome without cilia. The operculum mamillate to rostrate. Setae long; flexuose (thin).
Ecology. Mesophytic; occurring in neutral pH conditions to acid conditions, or acid conditions (often on shaded sandstone rocks and rotting wood).
Cytology. Haploid chromosome number, n = 12, or 20 and 22.
Representation in Britain and Ireland. 2 species. Orthodontium. Southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, central southern England, southwest England, Isle of Wight, and Ireland (O. lineare being common, and O. gracile widespread but rare).
Classification. Class Bryopsida; Subclass Bryideae; Order Bryales.
Illustrations. • Orthodontium gracile (with assorted other taxa): Dixon. ORTHODONTIACEAE: D. Orthodontium gracile Br. Eur. MNIACEAE: B, Mielichhoferia elongata (Hoppe & Hornsch. ex Hook.) Hornsch.; E, Pohlia elongata Hedw. ssp. polymorpha (Hoppe & Hornsch.) Nyh.; F, Pohlia elongata Hedw. ssp. elongata; G, Pohlia elongata Hedw. ssp. acuminata (Hoppe & Hornsch.) Hüb.; H, Pohlia cruda (Hedw.) Lindb.; I, Pohlia nutans (Hedw.) Lindb. BARTRAMIACEAE: A, Breutelia chrysocoma (Hedw.) Lindb.; C, MEESIACEAE: Leptobryum pyriforme (Hedw.) Wils.
From Dixon (1924), the unscaled screen display approximately doubling the magnifications given with his individual figures. 1, leaf, or stem leaf where these differ; 2, branch-leaf; 3, perichaetial leaf; 4, perigonial leaf; 5, capsule; 6, peristome; 7, calyptra; 8, spores; 9, inflorescence; 10, gemmae; 11, paraphyllia; 12, stoma of capsule; *, plant, or part of one. Qualifications: a, apex; b, base; c, cells at one third from the apex; cv, ventral aspect of cells; cd, dorsal aspect of cells; bc, basal cells; x, section. • Orthodontium gracile (details, with Bryaceae and Meesiaceae): Berkeley. ORTHODONTIACEAE: 4, Orthodontium gacile Br. Eur.; a, habit; b, leaf; c, calyptra; d, capsule; e, part of the outer peristome. BRYACEAE: 1, Plagiobryum zierii (Hedw.) Lindb.; a, habit; b, leaf; c, leaf cells; d, capsule. 2, Rhodobryum roseum (Hedw.) Limpr.; a, habit; b, leaf; c, capsule; d, part of the outer peristome; e, part of the inner peristome. MEESIACEAE: 3, Leptobryum pyriforme (Hedw.) Wils.; a, habit; b, leaf; c, capsule.
From Berkeley (1863, Plate 18). The approximate 1 cm scale applies to the whole plant (habit) illustrations only.
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, 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. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The moss families (Bryophyta, Musci) of Britain and Ireland. Version: 5th August 2019. delta-intkey.com’.
