2. Cyrtomnium Holmen, Bryologist. 60: 138, figs. 1, 2. 1957. • [Greek kyrtos, curved or arched, and mnion, moss, alluding to capsules].
Norton G. Miller, Gert Steen Mogensen
Plants (0.5-)2-7(-20) cm, in tufts or mats. Stems brown or black with age, erect, inclined, arching, or ± plagiotropic, simple, irregularly and sparingly branched, or branched distally, not dendroid; rhizoids brown or reddish brown, macronemata present, not in longitudinal rows, micronemata present or absent. Leaves often bluish green or green, brownish or reddish when old, crisped or not when dry, erect or erect-spreading, flat or somewhat undulate when moist, ovate or broadly elliptic, 1-2(-2.5) mm; base not to long-decurrent; margins plane, green or bluish green, 1-stratose, entire; apex obtuse, acute, or rounded, apiculate or not; costa subpercurrent or percurrent, distal abaxial surface smooth; medial laminal cells ± isodiametric or short-elongate, 22-45 µm, often in longitudinal and diagonal rows, weakly collenchymatous, walls weakly pitted; marginal cells differentiated, linear or short-linear, sometimes rhomboidal, in 1-3 rows. Specialized asexual reproduction from fragile stem fragments, plants sometimes breaking only near stem apex. Sexual condition dioicous. Seta single, brown, 3-4 cm, straight. Capsule strongly inclined to horizontal, brown, cylindric, 4-5 mm; stomata phaneroporous; operculum short-apiculate; exostome yellow; endostome pale yellow, . Spores 13-25 µm.
Species 2 (2 in the flora): n North America, Europe, Asia.
The phaneropore stomata in Cyrtomnium are unique in Mniaceae, and the reduced endostome cilia are also unusual for the family. These mosses are distinguished morphologically and by habitat preference. In both species, plant stems break easily, and field populations often consist of loose fragments and plants anchored to the substratum, intermixed with other mosses. The outer laminal cell walls have a hygroscopic coating and, as a result, fragments float in water. Thus, local dispersal in these species may be by moving water or by wind, which apparently moves fragments in tundra. Plants of both species often display bluish green leaves. Cyrtomnium is a genus mainly of Arctic and subarctic regions. However, C. hymenophylloides is found far southward as a relict in lowland gorges or in mountains.