Plants medium-sized, with red secondary coloration (entirely green plants not seen); branch and shoot apices not pencil-like; cells of stem epidermis widened in part of stem circumference and forming a partial hyalodermis; pseudoparaphyllia foliose, broadly ovate to slightly wider than long, with rounded to irregular apex; axillary hairs with 1--3-celled distal portion, hyaline when young. Stem leaves straight and erect or weakly homomallous, gradually narrowed to an acuminate or shortly acuminate, sometimes blunt apex from an ovate or triangular-ovate base, apex sometimes incurved over leaf, concave, near apex channeled to almost tubular; margins entire or at most in part very finely, obtusely denticulate; costa ending shortly below leaf apex; alar cells in distinctly delimited, transversely triangular group that reaches costa or almost so, not decurrent, supra-alar cells weakly differentiated or forming a zone of small cells between alar cells and cells above. Sexual condition dioicous.

Apparently in spring-influenced habitats or along the shores of brooks; 0--1700 m; Nun., Yukon; Alaska; endemic to North America.

This species is superficially similar to Warnstorfia sarmentosa in habit, with rather thick shoots and short and often curved branches with obtuse endings due to densely inserted and relatively shortly acuminate leaves. However, the leaves are distally more gradually narrowed leaves in W. pseudosarmentosa than in W. sarmentosa, and the usually acuminate or shortly acuminate leaf apices in the first of these species make the separation easy. Warnstorfia pseudosarmentosa is close to W. exannulata, from which it differs mainly in the more strongly concave leaves that are mostly deeply furrowed to almost tubular in their distal portion, and in its entire leaf margins. Sometimes the stem leaf lamina is also weakly plicate (in moist condition) in W. pseudosarmentosa, something which does not occur in W. exannulata. Few specimens of W. pseudosarmentosa were available for study and it is therefore difficult to judge its correct status. It may be a good species, or it may represent an extreme, Arctic modification of W. exannulata.