Specialized asexual structures are usually present. Seta 6--14 mm, erect, straight or ± flexuose, superficial cells smooth and spirally twisted the entire length or spirally twisted and interspersed with sections of prorulate straight cells. Spores 10--13 µm.
Varieties 2 (2 in the flora); circumpolar.
Using growth studies, R. T. T. Forman (1962) suggested that leaf width and shape were influenced by temperature but could be used for species determination in some areas of North America, although it appears to be an inconsistent character and should be used with caution to determine sterile material. The varieties are distinguished by twisting of the superficial cells of the seta in both old, dry, and young, fresh material; the seta itself is twisted when dry.