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Key to Calamagrostis

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1 Inflorescences dense and spikelike, symmetrical, cylindrical or ovoid, unbranched
  2 Ligule 1-4.6 mm long
1 Inflorescences loose and open, or if relatively dense, then with discernible branches, and thus lobed or asymmetrical.
    3 Callus hairs > 1.3× as long as the lemma; rachilla prolonged beyond the palea; [rare introduction from s. NJ northward]
    3 Callus hairs < 1.2× as long as the lemma; rachilla not prolonged beyond the palea; [natives, sometimes weedy, widespread].
      4 Awns attached on the upper 2/5 of the lemmas, 0.5-2 mm long, straight
      4 Awns attached on the lower ½ of the lemmas, 0.9-6 mm long, straight or bent.
        5 Awns usually exserted, (2.8-) 3-6 mm long; callus hairs 0.3-0.7× as long as the lemma.
          6 Leaves (1-) 2-3 (-4) mm wide; plant densely tufted, delicate, culms 10-55 (-60) cm tall, with 2-3 nodes; [high elevation rock outcrops and glades]
          6 Leaves (2-) 3-8 (-12) mm wide; plant rhizomatous or loosely tufted, coarse, culms (60-) 75-120 cm tall, with 3-5 nodes; [low to moderate elevation forests and woodlands].
             7 Leaves glaucous above and below; leaf collars glabrous
             7 Leaves glaucous above, dark green below; leaf collars with prominent tufts of hairs
        5 Awns usually not exserted, 0.9-3.1 (-4) mm long; callus hairs (0.5-) 0.7-1.2 (-1.5)× as long as the lemma.
               8 Callus hairs < 1 mm long, 0.2-0.3× as long as the lemma
               8 Callus hairs > 1 mm long, (0.5-) 0.7-1.2 (-1.5)× as long as the lemma
                 9 Glumes smooth (or scabrous on the keel only); awns stout, readily distinguished from the callus hairs
                 9 Glumes scabrous on the keel and often also the surface; awns delicate, difficult to distinguish from the callus hairs.
                   10 Spikelets 2.5-4 mm long; lemmas usually shorter than the glumes; glumes rounded to broadly keeled, with raised midveins; glume apices usually acute, rarely acuminate
                   10 Spikelets 2-3 mm long; lemmas usually about as long as the glumes; glumes rounded, midveins not raised; glume apices acute