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Key to Muhlenbergia

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1 Panicle open and diffuse, > 4 cm broad, ultimately appearing broad and not spikelike; the spikelets borne separately on slender or capillary pedicels longer than the lemmas or borne tightly and appressed on diverging spikelike branches.
  2 Spikelets mostly sessile, not borne on capillary pedicels, tightly appressed to the panicle branches; panicle branches strongly divergent; [subgenus Pseudosporobolus]
  2 Spikelets borne on slender or capillary pedicels (pedicellate), not appressed tightly to panicle branches, individual panicle branches not spikelike; branches primarily ascending (sometimes weakly divergent).
    3 Spikelets 1.1-2.2 mm long; spikelets with 1 floret, occasionally 2 or 3.
      4 Plants without rhizomes, instead tufted with erect culms (bunched); Spikelets 1.5-2 mm long; lemmas awnless; [subgenus Pseudosporobolus]
      4 Plants not cespitose, rhizomatous, the rhizomes prominent, creeping, and covered with imbricate scales; awns of the lemma 1.1-2.2 mm long.
        5 Culms compressed-keeled, ascending; blades conduplicate (folded lengthwise), 6-20 cm long; panicles cylindrical, 10-28 cm long, 4-8 cm wide; [subgenus “incertae sedis”]
        5 Culms terete to somewhat compressed-keeled near the base, decumbent-ascending; blades usually flat, occasionally conduplicate, 2-7(-11) cm long; panicles ovoid, 6-21 cm long, 4-16 cm wide; [subgenus Pseudosporobolus]
    3 Spikelets 2.5-5 mm long (excluding awns); spikelets with 1 floret [subgenus Trichochloa].
          6 Lemma awn 0-1.5 (-4) mm long; glume bodies (1.1-) 2.0-3.3 (-3.6) mm long, < ½ as long as the lemma bodies, acuminate, not awned (rarely the second with a short awn < 0.6 mm long); spikelets usually brown or bronze (when fresh); basal sheaths usually very fibrous
          6 Lemma awn (2-) 3-35 mm long; glume bodies (0.3-) 0.7-1.7 (-2.4) mm long, > ½ as long as the lemma body, one or both glumes sometimes awned; spikelets usually purple (when fresh); basal sheaths rarely strongly fibrous.
             7 Lemma awn (2-) 3-13 (-18) mm long, first glume awnless (or rarely with an awn to 3.2 mm long), second glume awnless (or rarely with an awn up to 5.0 mm long), palea awnless; lemma lacking setaceous teeth flanking the awn; flowering late Aug-Oct; [widespread in our area, particularly in rocky, clayey, or sandy glades, barrens, and woodlands with prairie affinities]
             7 Lemma awn (8-) 12-26 (-35) mm long, first glume awn (0.5-) 1-7 (-10) mm long, second glume awn (1-) 5-19 (-25) mm long, palea awn-tipped; lemma with two setaceous teeth flanking the awn, the teeth 0.5-2.5 (-4.7) mm long; flowering Oct-Nov; [sandy maritime situations on barrier islands of the outer Coastal Plain]
1 Panicle slender, dense, < 2.5 cm broad, ultimately appearing spikelike, the spikelets sessile or on non-capillary pedicels shorter than the lemmas; [subgenus Muhlenbergia].
               8 Glumes minute, 0-0.5 mm long; plant lacking rhizomes; culms weak, decumbent and cespitosely branching in their lower portions, rooting at the nodes, the upper portions erect and sparsely branched
               8 Glumes well-developed, 1-8 mm long; plant with scaly rhizomes (except for M. cuspidata); culms firm (rarely sprawling), few or solitary (rarely forming dense colonies).
                 9 Glumes 3-8 mm long (tapered to arched or straight awns), 1.3-2x the length of the lemma (excluding its awn); panicle dense and spike-like, 0.8-16 cm long and 0.3-10 mm broad.
                   10 Culms with little to no branching above the base; internodes dull and puberulent, strigose directly below the nodes; awns of the glumes to 5 mm long; ligules 0.2-0.6 mm long
                   10 Culms much-branched above the base; internodes smooth, polished, and mostly glabrous (sometimes puberulent directly below the nodes); awns of the glumes to 1 mm long; ligules 0.6-1.7 mm long
                 9 Glumes 1.2-3 mm long, shorter than to barely exceeding the lemma; panicle usually slender, arching, generally less dense and not spike-like, often with some elongated (though appressed) branches, 4-50 cm long, 2-15 mm broad.
                     11 Callus glabrous; plant lacking scaly rhizomes (with slender stolons and a hard, knotty crown); leaves 0.5-2 mm wide; [calcareous cliffs]
                     11 Callus bearded (sometimes only slightly so) (glabrous in M. glabriflora); plant with scaly rhizomes (except for M. tenuifolia); leaves (1-) 2-14 mm wide; [various habitats].
                       12 Awns of the lemma 0.1-12 (-13) mm long; [collectively widespread]
                          13 Panicle linear, loosely flowered, much exceeding the leaves; culm erect, simple or sparingly branched; glumes relatively broad, the body ovate, 1.2-2.5 mm long, abruptly narrowed to the acuminate tip; ligule obsolete or shorter than the elongate cartilaginous summit of the leaf sheath.
                            14 Lemmas awnless or awn < 0.5 mm long; spikelets 1.5-2.5 mm long; leaf blades usually (1-) 2-6 mm wide
                            14 Lemma awn 1-11 mm long (rarely awnless); spikelets 3-5 mm long; leaf blades (2) 6-10 (-13) mm wide (often > 8 mm wide)
                          13 Panicle lanceolate, densely (rarely loosely) flowered, leaves often extending conspicuously into the inflorescence; culm geniculate, freely branched; glumes relatively narrow, the body lanceolate, 2-3 mm long, tapering from base to apex; ligule usually obvious above the short cartilaginous summit of the leaf sheath.
                                  17 Lemma awn 7-12 mm long; spikelets loosely clustered, on pedicels 2-4 mm long
                                  17 Lemma awnless or with a short awn tip (rarely to 9 mm long); spikelets densely clustered, on pedicels < 1 mm long.
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