Flower:

A spike-like panicle at the tip of the stem 1½ to 5 inches long, with erect to slightly spreading branches mostly less than 1 inch long, and often a distinct gap between the lowest branches and those above. Spikelets (flower clusters) are somewhat crowded along a branch, somewhat compressed, 5 to 7 mm (to ~¼ inch) long, often purple-tinged, and have a single floret.

At the base of a spikelet is a pair of bracts (glumes), both awnless, keeled, usually rough-textured, tapering to a sharply pointed tip, 5 to 7 mm long, as long as the spikelet. Florets are surrounded by a pair of bracts (lemma and palea), the lemma thin, 4 to 5 mm long, shorter than the upper glume, notched with 4 teeth at the tip, and with an awn arising from near the base of the back that extends about 1 mm beyond the tip of the glumes; awns are initially straight, becoming bent and twisted below the bend; the palea is somewhat shorter than the lemma. The thickened base of the floret (callus) is densely covered in straight, white hairs that are usually less than half as long as the lemma; a stalk (rachilla) also covered in long hairs extends up to 2 mm above the callus.

Leaves and stems:

Leaves are erect to ascending, basal with 2 or 3 alternate stem leaves, 2 to 5 mm wide, 2 to 7 inches long, initially flat becoming rolled in along the edges (involute), and green to blue-green. The upper surface has raised veins and is moderately to densely covered in short, stiff hairs.

The sheath is hairless, smooth to somewhat rough. The ligule (membrane where the leaf joins the sheath) is 2 to 4 mm long, ragged or shredded along the tip edge and lacks a fringe of hairs. Nodes are smooth. Stems are erect, hairless, unbranched, multiple from the base forming clumps, with old basal sheaths often persisting and becoming fibrous.

Fruit:

At maturity, branches become appressed and spikelets turn straw-colored to pale brown, the florets dropping off individually leaving the glumes behind on the stalk. Grains are amber brown, oblong, about 1.6 mm long.

Notes:

Purple Reedgrass is very rare in Minnesota, currently known from only 2 sites near the Canadian border in northern Cook County. According to the DNR, there are only 4 historical records at 3 different lakes in the area, causing it to be listed as a Special Concern species in 1996 pending new biological surveys. Since then, the area has been heavily botanized and only 1 of those sites relocated and 1 additional site found; it was subsequently elevated to Endangered in 2013. In the bulk of its range it is found in alpine meadows, tundra, sand dunes and even open forests, but in Minnesota it is restricted to the crevices and ledges of tall cliffs.

Purple Reedgrass is recognized by its clump-forming habit, stems to 30 inches tall; only 2 or 3 stem leaves 2 to 5 mm wide, green to blue-green, flat or in-rolled edges, short-hairy on the upper surface; spike-like panicle of 1-flowered spikelets 5 to 7 mm long; both glumes hairless, awnless, equal in size and shape, longer than the floret; callus and rachilla covered in long, straight hairs, callus hairs usually less than half as long as the lemma; lemmas 4-toothed at the tip; lemma awns arising from near the base of the back, slightly to strongly bent, extending about 1 mm beyond the tip of the glumes.

Similar species are the related Slimstem Reedgrass (Calamagrostis stricta), which is found in wetter habitats such as fens and wet prairies, and Plains Reedgrass (Calamagrostis montanensis), which is only found in western Minnesota, both of which lack the hairs on the upper leaf surface and have lemma awns that barely extend beyond the glumes, if at all.