Muscologia Recentiorum, Suppl. 4: 132 (‘1819’) [1818].

For the genus type description, we refer to Vitt (1983) and Vitt & Ramsay (2006). We only mention below the main distinguishing features in the New Caledonian context. Macromitrium plants are epiphytic on trunk, branches or twigs, rarely saxicolous, characterized by: 1) creeping stems giving rise to dense upturned branches, simple to bifurcate, rarely fastigiated; 2) stem and branch leaves usually different in shape; 3) branch leaves with different habits in dry and moist conditions, when wet usually straight to recurved or sigmoid, more or less widely spreading, when dry the various arrangements are important for species discriminating; and 4) branch leaf areolation usually different from top to down, typically with three different parts, this pattern being very useful to identify the species: – upper part usually single-layered, rarely multi-layered in patches or limited to apices, opaque, green to red tinged, with cells isodiametric to short oblong, flat or bulging, usually with a few small papillae, rarely smooth, mostly irregularly arranged, less frequently in regular longitudinal files, – transitional part short or long, variously green becoming colourless top-down, unfrequently null with abrupt transition to lower part, possibly reaching the base in some groups of species, transitional cells progressively longer toward base, oblong to short rectangular, with single papillae, rarely smooth; – lower part developed or not, then reduced to a few elongate cells in one or few basal rank, when developed colourless, with more or less elongate cells, rectangular to linear, thick-walled or not, regularly so or not, in relation to lumina wideness and orientation, straight, curved or sinuous, papillae single, rounded, low to high, usually scattered, aligned or not on plicae or margins, more rarely dense or absent; 5) costae single, strong to thin, reaching the apices, percurrent, often excurrent in mucrones, less frequently in more or less long aristae; 6) margins plane, in some case narrowly recurved in one side at base, at most crenulate-papillose in upper part, rarely smooth, usually smooth in basal part, or with scattered papillae; 7) when known, sexual condition pseudautoicous, very rarely autoicous, dwarf male plants present on the female branches, at vegetative leaves axils; 8) perichaetia are significantly conspicuous when exceeding the vegetative leaves, sheathing or not the seta bases, more often inconspicuous, perichaetial leaf size being then similar to the vegetative ones or smaller; when differentiated, perichaetial leaves larger or not, mostly hyaline, the short celled, opaque upper tissues restricted to small part below the apices, papillose or not; 9) setae upright, straight to sinuous, either medium to long and thin and twisted to the left or short and thick untwisted or shortly below the urn; 10) vaginulae either naked, possibly with short paraphyllae, or hairy with conspicuous long hairs visible among the perichaetial leaves or longer, sometimes reaching the capsule; 11) calyptrae large, mitrate, usually covering a large part of the capsule, very rarely conspicuously shorter, naked or with more or less dense hairs, erect or rarely bristling; 12) capsules erect, ovoid, elliptic or unfrequently cylindrical, rims contracted or not, plicate or smooth, erect or incurved, rarely collapse, brownish or concolorous; 13) peristomes single or absent, teeth sometimes very short or caducous or reduced to short membranes; and 14) spores papillose, usually anisomorphic, rarely isomorphic.