Seta superficial cells usually lightly papillose near the base, cells spirally twisted but interspersed with sections of straight, prorulate cells.
Capsules mature spring-early summer. Rare, on well-decayed wood, stumps, and logs; B.C., N.B., Nfld. and Labr. (Labr.), N.W.T.; Colo., Mont., Wyo.; e Asia (Russian Far East).
Variety trachypoda has been synonymized under both Tetraphis geniculata and T. pellucida. It proved, in fact, to be a form intermediate between these species. It occurs in North America and Russia, although at the present time the geographic range in Russia is little known. Based on the North American material examined it appears to be found only in areas where both T. pellucida and T. geniculata occur, suggesting that it might be found in the Russian Far East where the two species also overlap.
: 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. Throughout Northern Hemisphere.
Varieties 2 (2 in the flora). Using growth studies, R. T. T. Forman (1962) suggested that leaf width and shape are 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.