Calamagrostis purpurascens is an erect, perennial tufted grass, that grows in well-drained areas in Denali, from the boreal zone into high alpine areas (occurring primarily north of the Alaska Range crest), including gravel bars, open soil on slopes, grassy meadows, and stony south-facing tundra. Individuals of this species typically have old, dried leaf blades persistent at the base of the plant. Scabrous and stiff stems arising from a stout rhizome and grow to 20-70 cm in height. Leaves are scabrous, flat, becoming involute with age, 2-4 mm wide and much shorter than the stems. Inflorescence is a spike-like, compact panicle, 6-8 cm long. Spikelets contain a single bisexual floret. The two glumes are of different lengths. A distinctive, long (4.5-8mm) exserted geniculate (bent) awn is attached at the base of the lemma. The callus hairs are shorter than lemmas. Fruits are single-seed, indehiscent and dry. The presence of the geniculateawn separates this plant from other Calamagrostis species in the park.
Calamagrostis purpurascens greens up in early summer and produces flowers in mid to late summer.
Calamagrostis purpurascens is monoecious, with stamens and pistils in the same florets (bisexual). Flowers are wind pollinated and seeds are wind disseminated. C. purpurascens can also reproduce vegetatively by rhizomes.
Calamagrostis purpurascens is the host plant for the Arctic Skipper butterfly (Carterocephalus palaemon) (Scott 1986).
Calamagrostis purpurascens has been used for restoration of disturbed sites in subalpine and alpine ecosystems.
Calamagrostis purpurascens has a widespread, amphi-Beringian distribution. In North America, this species occurs from Alaska east across the Arctic to Greenland, and south through the Pacific states and Rocky Mountains to New Mexico. Calamagrostis purpurascens also occurs in Minnesota and South Dakota. Calamagrostis purpurascens occurs in scattered sites across the northern part of Denali, also with a few stations south of the Alaska Range. Calamagrostis purpurascens occurs most frequently in the northeastern hills and mountains of the park.
Calamagrostis purpurascens is a moderate-high elevation species that is seen in Denali from 187 m to 1676 m with an average plot elevation of 870 m. Most plants were seen at elevations above 900 m. It is most common on south, southwest, and southeast facing slopes. Although it is found in plots with slopes from 0 to 47 degrees, it prefers steeper slopes with an average plot slope of 17 degrees. It occurs sporadically in dry sites at low elevations.
Calamagrostis purpurascens typically grows in open, dry, well drained sandy to rocky slopes and ridges, along lakeshores, and in open woods. This species thrives in full sunlight and is usually indicative of calcareous soils.