By far the most abundant moss in Denali (and one of the most abundant plants in the state), stairstep moss is found in large mats in a variety of habitats. Plants are green-gold to yellow-reddish. It is recognized by its red stems, twice-branched branches and a unique growth pattern which produces 'stair-steps' along the stem. Each 'step' is approximately a year's worth of growth. The stem is red, covered in tiny reddish hairs (paraphyllia). This species can look superficially similar to the also abundant Pleurozium schreberi, but that species lacks the stair-step pattern, is not twice-pinnate, and its red stems do not have paraphyllia. Pleurozium schreberi also appears more glossy when dry.

This species very rarely reproduces sexually. It primarily spreads through fragmentation and vegetative growth, though sporophytes are sometimes seen.

Stairstep moss is frequently used as a biomonitoring species because of its frequency, abundance, and approximate annual growth pattern.

Circumboreal, with scattered locations in the southern hemisphere.