Rhizomes elongate or compact, 1.5-3 mm thick, with 8-35 mm scales, glabrous. Culms 10-150 cm tall, 1.2-7 mm thick. Ligules 2-7(15) mm; blades 1-36 cm long, 1.5-15 mm wide. Panicles 2.5-17(44) cm long, 0.7-10(14+) cm wide, often narrow and stiffly erect, sometimes loosely contracted or approaching conical; branches 0.5-13 cm, with 3-140 spikelets. Spikelets 3-6.5 mm. Lower glumes 1.8-4.5 mm; upper glumes 2.3-5.5 mm; lemmas 3-6.5 mm; anthers 1.3-4 mm.

Arctagrostis latifolia grows in a wide range of habitats, from sea level to 2000 m, and exhibits considerable phenotypic plasticity. Infection by nematodes leads to the formation of enlarged dark purple ovaries. Such forms have been annotated as forma prolifera or forma vivipara, but these names have no taxonomic validity.

The two subspecies overlap in their morphology, mainly because of phenotypic plasticity, but A. latifolia subsp. arundinacea, which grows in the low arctic of Alaska and northern Canada, is usually larger than subsp. latifolia, which grows in the high Arctic. Agronomic studies appear to have utilized only subsp. arundinacea.