Meesiaceae Schimp.

Plants medium-sized to ± robust, erect, dull or weakly glossy, often dark brown or nearly black below, forming turves. Stems erect, sparsely branched by innovation or forking, densely or sparsely covered with dark, papillose rhizoids, in cross-section with a distinct central strand. Leaves erect, erect-spreading, or widely squarrose, with an erect base, often distinctly ranked in 3 to many rows, uniformly spaced and sized or less often crowded and larger in an apical coma (in Leptobryum), ovate-lanceolate, obovate, or lanceolate-subulate (in Leptobryum), not or clearly decurrent, unbordered, mostly entire but sometimes toothed near apex; upper laminal cells variable in shape, smooth (in N.Z. taxa) or rarely mammillose, mostly firm- or thick-walled. Costa broad, ending below the apex or percurrent. Axillary hairs conspicuous, with 2–3 strongly pigmented basal cells. Rhizoidal tubers absent or present (in Leptobryum).

Sexuality variable. Perichaetia terminal, often appearing lateral due to innovation; perichaetial leaves longer than vegetative, enclosing sex organs and a few filamentous paraphyses. Perigonial leaves usually forming a disc, enclosing numerous clavate paraphyses (in Meesia). Setae elongate, thin, and often tortuous; capsules usually suberect, sometimes horizontal to pendulous (in Leptobryum), curved from a conspicuous and often elongate neck, asymmetric, elongate-pyriform; stomata numerous in the neck; operculum bluntly conic. Peristome double, highly variable; exostome teeth usually much shorter than endostome segments (in Meesia) or ± equal the endostome segments (in Leptobryum); endostome with a low or high basal membrane, with or without cilia. Calyptra cucullate and smooth. Spores spherical, variable in size and ornamentation.

A family traditionally considered (Brotherus 1924) to consist of three predominantly northern hemisphere genera: Meesia, Paludella, and Amblyodon (the last two monotypic). Matteri & Ochyra (1999) reviewed the members of the family (three species in three genera) occurring in southern South America, while Bell & Catcheside (2006) treated the two species of Meesia recorded from eastern Australia. Goffinet et al. (2009) recognised five genera in the family, including Leptobryum (which has traditionally been treated in the Bryaceae) and the monotypic southern South American Neomeesia.

The placement of Leptobryum in this family by modern authors is based on the molecular evidence presented by Cox & Hedderson (1999). Counter arguments, in favour of retaining Leptobryum in the Bryaceae, are presented by Ochyra et al. (2008, p. 419).

The genera placed in Meesiaceae by Brotherus have often poorly developed exostome teeth, low endostomal basal membranes and rudimentary or no cilia. Leptobryum, by contrast, has essentially a perfect peristome with well-developed and lanceolate exostome teeth, a high endostomal basal membrane with well-developed segments and well-developed appendiculate cilia. By these and many other features (including costal anatomy and the nature of its laminal cells), Leptobryum is morphologically anomalous in this family. It is retained here because of Cox & Hedderson’s molecular evidence that it belongs in a well-supported clade that includes Meesia, Paludella, and Amblyodon. This interpretation led to its inclusion in the Meesiaceae by Goffinet et al. (2009). Leptobryum is also placed in the Meesiaceae in Smith’s (2004) British flora and in the classification utilised by the Flora of Australia vol. 51, which is based on Goffinet & Buck (2004).