Stems (0.5-)1-2(-3) cm. Leaves 2-3(-3.5) mm, linear-lanceolate, apex more or less acute; margin weakly recurved for a short portion of the leaf length or sometimes almost plane, 2(-3)-stratose; laminal cells smooth or with scattered papillae distally, mainly on the abaxial side, distal cells about 7-10 µm. Perigonium sessile. Seta (0.5-)0.6-0.7(-1) cm, straight wet or dry. Capsule straight and erect, not strumose; annulus weakly developed.

Capsules mature summer. Rocks, tree boles, soil; moderate elevations; Greenland; Alta., B.C., Man., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Alaska, Maine, Minn., Mont., S.Dak.; Eurasia; Atlantic Islands (Iceland).

The distribution of Cynodontium tenellum is fairly well understood for Canada but not for the United States because of confusion with 3. C. alpestre (see discussion thereunder). The present treatment follows W. C. Steere (1978) and R. R. Ireland et al. (1987). The problem in nomenclature of C. tenellum is still unresolved (G. S. Mogensen 1980; B. H. Allen 2005).