Plants perennial; shortly rhizomatous. Culms (6)10-80 cm, erect or decumbent. Ligules 1-2 mm, truncate; blades 4-22 cm long, 2.5-7 mm wide; upper sheaths inflated. Panicles 1-5 cm long, 8-14 mm wide. Glumes 3-5 mm, connate at the base, membranous, densely pilose throughout, keels not winged, ciliate, apices acute and parallel; lemmas 2.5-4.5 mm, connate at the base, glabrous below, finely pubescent apically, apices usually obtuse, occasionally truncate, awns 2-6(8) mm, geniculate, exceeding the lemmas by 0-5 mm; anthers 2.3-3 mm, yellow. Caryopses 0.7-2 mm. 2n = 98, 100, 105, 112, 117, 119, ca. 120.
Alopecurus borealis has an arctic-alpine to subalpine circumpolardistribution, but it has not been found in Scandinavia or Iceland. It grows primarily in wet soils in tundra, meadows, along streams, shorelines, gravelbars, and floodplains, and occasionally in somewhat drier forest openings, in fine or silty to stony soils or moss. It is sometimes co-dominant with Dupontia fisheri in the arctic and subarctic portion of its range. The anthocyanic tint of the plant as a whole greatly increases to the north.
The morphological variability in Alopecurus borealis has prompted recognition of several segregate taxa. Alopecurus stejnegeri Vasey and A. occidentalis Scribn. & Tweedy are two of the more conspicuous extremes. The former are small plants occurring on enriched sites in the Arctic, usually around sea bird or seal colonies where high nutrient levels produce lush vegetative growth; the latter refers to tall-stemmed plants found in the Rocky Mountains. Because such plants are simply extremes in a continuum of variation, they do not merit taxonomic recognition.
Alopecurus borealis is listed in many floras as A. alpinus Sm., a name that had previously been applied to another species. The correct name is A. borealis.