Ditrichaceae
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Plants minute or rather small to medium-sized, gregarious or loosely to densely tufted. Stems erect, simple or forked, with a central strand. Leaves mostly lanceolate, acuminate or subulate, straight or somewhat curved, rarely sheathing at base; in numerous rows (2 rows in Distichium); costa single, well developed, subpercurrent to excurrent, in section with 1 row of guide cells and 2 stereid bands, adaxial band sometimes much reduced; lamina cells smooth (± roughened in subula in Distichium); basal cells elongate, narrower towards the margins, those of basal angles not differentiated or forming a marginal border; distal cells isodiametric or short-rectangular to elongate, walls firm. Specialized asexual reproduction occasional, as multicellular filamentous gemmae borne in axils or along stems, or as specialised tubers or filamentous propagules on rhizoids. Sexual condition dioicous, autoicous, paroicous, or synoicous; perigonia axillary or on short branches adjacent to perichaetia, or terminal on separate plants; perichaetial leaves not markedly differentiated or with a longer, broader sheathing base and shorter subulate apex. Seta short to ± elongate, yellow to orange, reddish brown, brown, or reddish purple; capsules immersed to emergent and subglobose to long-exserted and ± cylindric, erect to inclined or pendulous, often ± curved or asymmetric; cleistocarpous, gymnostomous, or peristomate; annulus, when present, usually of 2-3 rows of larger cells, deciduous; peristome, when present, single, of 16 teeth, variously split into two terete filaments or perforate to near the base; operculum conic to short-rostrate. Calyptra cucullate, rarely mitrate. Spores spheric to ovoid or ± reniform, finely to coarsely papillose, verrucose, or somewhat vermicular or reticulate. Species of Ditrichaceae usually colonize soil, rarely wood, and some species have a distinct preference for calcareous substrates. The family is poorly defined and separated from Dicranaceae primarily on peristome characteristics, with the teeth divided into terete rather than flat filaments, and the general absence of vertical pit-striations. In some species, however, oblique ornamentation is present, at least in the distal portion of the teeth. W. R. Buck and B. Goffinet (2000) included 25 genera, with one hybrid genus, Pleuriditrichum, in the family. The inclusion of at least some of the genera seems somewhat anomalous. Within the flora, Ceratodon, Distichium, Ditrichum, Saelania, and Trichodon are peristomate, while Cleistocarpidium, Eccremidium, Pleuridium, and Pseudephemerum are cleistocarpic. Although in this treatment it is included in Ditrichaceae, Pseudephemerum was placed in Dicranaceae by Buck and Goffinet.

Britton, E. G. 1913b. Ditrichaceae. In: N. L. Britton et al., eds. 1905+. North American Flora. ..... 47+ vols. New York. Vol. 15, pp. 55-67.

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