Calamagrostis purpurascens is known from several sites on cliffs along the north shore of Lake Superior, as well as farther southeast in Ontario, and may be found on rock ledges on Lake Superior. It differs from all our other species in the long awns 4.5–9 mm long and pubescent upper surfaces of the leaves.
1. Callus hairs and glumes at least 1.5 times as long as the lemma.
1. Callus hairs and glumes barely if at all exceeding lemma.
2. Panicle mostly open with rather loosely ascending to spreading branches at flowering time; lemma nearly or quite smooth, membranous and translucent for at least the apical half; awn nearly or quite smooth, at least on basal half; callus hairs about as long as lemma (occasionally shorter), ± uniform in length and distribution; palea not over 2 mm long.
2. Panicle mostly narrow and contracted with strongly ascending branches at flowering time; lemma usually firm and prominently scabrous, colorless and translucent only toward the tip; awn distinctly but minutely antrorsely scabrous its entire length [20×]; callus hairs generally shorter than lemma, ± unequal in length or distribution (those immediately below the middle of the lemma shorter than those at the side, or absent; do not confuse the hairy prolongation of the rachilla behind the palea); palea often longer than 2 mm.
All species found in Calamagrostis
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. May 24, 2017. http://michiganflora.net/genus.aspx?id=Calamagrostis.