Hypnum pseudosarmentosum Cardot & Thériot, Univ. Calif. Publ. Bot. 2: 305, plate 27, fig. 2. 1906 (as pseudo-sarmentosum); Calliergon pseudosarmentosum (Cardot & Thériot) Brotherus; Drepanocladus pseudosarmentosus (Cardot & Thériot) Persson; Warnstorfia pseudosarmentosa (Cardot & Thériot) Tuomikoski & T. J. Koponen

Plants medium-sized, with red secondary pigment. Stems with branch and shoot apices not pencil-like; epidermal cells widened in part of stem circumference, forming partial hyalodermis; axillary hair distal cells 1-3, hyaline when young. Stem leaves ovate or triangular-ovate, gradually narrowed to apex, straight or almost so, strongly concave; base not decurrent; margins entire or in part minutely, obtusely denticulate; apex acuminate or sometimes blunt, ; costa ending shortly below apex; alar region from margins to costa or nearly so; .

Spring-influenced habitats, along brook shores; low to high elevations (0-1700 m); Nunavut, Yukon; Alaska.

Sarmentypnum pseudosarmentosum superficially similar to S. sarmentosum in habit, with rather thick shoots and short and often curved branches with obtuse apices due to densely inserted and relatively short-acuminate leaves. However, the leaves are more gradually narrowed than in S. sarmentosum, and the usually acuminate or short-acuminate leaf apices in S. pseudosarmentosum make the separation easy. Sarmentypnum pseudosarmentosum is similar to S. exannulatum, from which it differs mainly in the more strongly concave leaves that are mostly deeply furrowed to almost tubular distally, and in its entire leaf margins. Sometimes the stem leaf lamina is weakly plicate (when moist) in S. pseudosarmentosum, which does not occur in S. exannulatum. Few specimens of S. pseudosarmentosum were available for study; it may be a good species or may represent an extreme, Arctic modification of S. exannulatum.