Mnium flagellare Sullivant & Lesquereux, Proc. Amer. Acad. Arts 4: 277. 1859

Plants small, often loosely growing with other bryophytes. Leaves incurved upwards when dry and moist; costal abaxial teeth of 1 cell; medial laminal cells irregularly shaped, slightly smaller near margins. Capsule with exostome short, blunt.

Capsules mature summer. Cliffs, humus, boulders, shaded habitats, forests, epiphyte on alder and birch; low elevations; Alaska; Europe; Asia.

Because of their growth habit and doubly serrate leaf margins, plants of Trachycystis flagellaris resemble species of Mnium at first glance. However, they are readily distinguished by the mammillose laminal cells and, when present, flagelliform branches. This mode of asexual reproduction is also observed in Dicranum flagellare (Dicranaceae).