Nearly worldwide, circumtemperate to circumboreal.
Genera 12, species 92 (8 genera, 37 species in the flora).
Mniaceae is a diverse family generally characterized by relatively large plants with broad leaves, and with short-elongate or more or less isodiametric laminal cells most often hexagonal and angular. Leaf margins are usually differentiated by a border of elongate cells and range from smooth to strongly toothed. The family is also characterized by a wide degree of morphological variation as a response to environmental conditions, age, or sexuality. Fertile stems are sometimes strikingly different from sterile stems, and female or synoicous plants are sometimes different from male plants. This makes the identification of weakly developed specimens difficult. Many species in the family are fairly common in temperate and boreal habitats in the Northern Hemisphere and are frequently collected in ecologically based surveys.
The following keys stress vegetative traits and are best employed using well-developed, mature plants. Leaf laminal and marginal cell characters were derived by examining cells near mid leaf.
|1||Stems dendroid||> 2|
|1||Stems not dendroid||> 3|
|2||Branch leaves ovate-lanceolate.||Leucolepis|
|2||Branch leaves ligulate or lingulate.||Plagiomnium|
|3||Medial laminal cells mammillose; specialized asexual reproduction by flagelliform branches; Alaska.||Trachycystis|
|3||Medial laminal cells smooth; specialized asexual reproduction absent or present, not by flagelliform branches; widespread||> 4|
|4||Leaf marginal teeth paired.||Mnium|
|4||Leaf marginal teeth single or teeth absent||> 5|
|5||Medial laminal cells usually 3+:1; marginal cells indistinctly differentiated.||Pseudobryum|
|5||Medial laminal cells 2:1 or less, rarely longer; marginal cells usually strongly differentiated||> 6|
|6||Plagiotropic or arching sterile stems usually present (absent in P. venustum); leaf margins toothed, teeth often well developed and sharp, sometimes nearly absent and blunt; stems lacking red pigmentation.||Plagiomnium|
|6||Plagiotropic or arching sterile stems usually absent, occasionally present; leaf margins entire or toothed, teeth weakly developed when present, usually blunt; stems sometimes reddish||> 7|
|7||At least some leaf margins toothed, teeth usually reduced, often appearing as small extensions of distal cell ends.||Mnium|
|7||Leaf margins entire||> 8|
|8||Macronemata in longitudinal rows, micronemata absent; costal abaxial stereid band U-shaped; endostome segments fused into dome.||Cinclidium|
|8||Macronemata not in longitudinal rows, micronemata present or absent; costal abaxial stereid band not U-shaped; endostome segments free||> 9|
|9||Mature stems brown or black, lacking red pigmentation; leaves ovate or broadly elliptic; margins 1-stratose; stomata phaneroporous.||Cyrtomnium|
|9||Mature stems often red or reddish brown; leaves obovate, elliptic, or rarely ± orbicular; margins 1-4-stratose; stomata cryptoporous.||Rhizomnium|