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Key to Glyceria

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1 Spikelets 10-40 mm long, linear, 5-15× as long as wide, terete or nearly so in cross-section; [section Glyceria].
  2 Lemma (6-) 7-8.5 (-10) mm long, acute to acuminate; palea longer than the lemma, extending 1.5-3 mm beyond the lemma apex
  2 Lemma 2.4-6.0 mm long, obtuse to notched; palea about as long as the lemma (ranging from shorter than the lemma and included, to projecting up to 1.5 mm beyond the lemma apex).
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    3 Lemma (3.5-) 4.0-6.0 mm long, the apex with 1-2 strongly developed lobes, and also often toothed between the lobes; leaf blades 2-12 cm long; primary panicle branches 1.5-9.5 cm long
    3 Lemma 2.4-4.8 mm long, the apex rounded or with a few poorly developed rounded teeth; leaf blades 9-32 cm long; primary panicle branches 3-17 cm long.
      4 Lemmas entire or nearly so, acute (to obtuse); upper surface of mid-stem leaf blades densely papillose
      4 Lemmas crenate, truncate to obtuse; upper surface of mid-stem leaf blades scabrous or pubescent.
        5 Lemmas hispidulous on the veins, the hairs ca. 0.1 mm long; leaf blades to 12 mm wide
        5 Lemmas scabrous on the veins, the prickles ca. 0.05 mm long; leaf blades to 18 mm wide
1 Spikelets 2.5-8 mm long, ovate to oblong, 1.5-3× as long as wide, laterally compressed in cross-section.
          6 Upper glumes 2.5-5 mm long, longer than wide; [w. VA and possibly NC northward]; [section Hydropoa]
          6 Upper glumes 0.6-3.7 mm long, if > 3 mm long, then shorter than wide; [collectively widespread]; [section Striatae].
             7 Inflorescence compact (at maturity), the branches stiffly ascending to appressed, the tips never nodding; ligule < 1 mm long.
               8 Inflorescence branches elongate, appressed; lower internodes of the inflorescence 2-8 cm long; spikelets with 3-4 flowers, 3.5-4 mm long; lemma 1.9-2.8 mm long; leaves 2-5 mm wide; [Mountains, rarely elsewhere]
               8 Inflorescence branches short, stiffly ascending; lower internodes of the inflorescence 0.8-2.0 (-2.5) cm long; spikelets with 4-7 flowers, 4-8 mm long; lemma 3.0-3.7 mm long; leaves 3-10 mm wide; [Coastal Plain, rarely disjunct inland to the Mountains of VA]
             7 Inflorescence lax and diffuse (at maturity), the branches spreading to somewhat ascending, the tips often nodding or drooping; ligule 1-6 mm long.
                 9 Glumes tapering from below midlength to the narrowly acute (< 45 degree) tips; lemmas > 2× as long as wide; [endemic to seepage at high elevations in the Great Smoky Mountains, NC and TN and nearby]
                 9 Glumes narrowing from midlength or above to the acute or rounded (> 45 degree) tips; lemmas < 2× as long as wide; [collectively widespread].
                   10 Lemma 1.4-2.1 mm long, the veins prominently raised.
                     11 Leaf blades 6-15 mm wide; anthers 0.5-0.8 mm long; culms 2.5-8 mm thick; [rare introduction]
                     11 Leaf blades 2-6 mm wide; anthers 0.2-0.6 mm long; culms 1.5-3.5 mm thick; [common]
                       12 Spikelets predominantly green or stramineous-green, 2-4 mm long; lemmas not (or barely) scarious-margined; inflorescence open or lax, the loosely ascending capillary branches divergent or reflexed in age; leaves more numerous on culms; [widespread in a variety of wetland habitats in the US]
                       12 Spikelets predominantly purple, 3-4.5 mm long; lemmas with broad scarious tips; inflorescence primarily ascendant; leaves fewer; [of cooler seeps, fens, and similar habitats; northern in distribution]
                   10 Lemma 1.8-4.0 mm long, the veins visible, but not raised; ligule 2-6 mm long.
                          13 Lemma 2.4-4.0 mm long, projecting conspicuously beyond the palea; spikelets 5-8 mm long, with (4-) 5-10 flowers
                          13 Lemma 1.8-2.5 mm long, more-or-less equal to the palea; spikelets 3-5 mm long, with 2-5 (-6) flowers