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Key to Bouteloua

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1 All spikelets unisexual, plants usually dioecious.
  2 Upper glumes of the pistillate spikelets white, rigid, and globose, terminated by 3 awnlike teeth; staminate spikelets 4-6 mm long; [section Buchloe]
  2 Upper glumes of the pistillate spikelets membranous and unawned; staminate spikelets 3-4 mm long; [section Opizia]
1 Lowest floret in each spikelet bisexual, the upper staminate or sterile.
    3 Panicle branches deciduous; disarticulation occurring at the base of the branch (the branch therefore falling whole); spikelets 2-3 per branch, appressed to the branch.
      4 First (proximal) spikelet on each branch with 1 floret, the other spikelets with 2 florets (1 bisexual and 1 rudimentary); plants annual; [exotic, reported on ballast]; panicle branches 1-15; [section Hirsuta; subsection Eriopoda]
      4 Spikelets all alike, each with 1 bisexual and 1-2 rudimentary spikelets; plants perennial; [native species of limestone habitats, also with introduced populations]; panicle branches 1-80.
        5 Central awns of lemmas flanked by 2 membranous lobes (1-1.5 mm long); upper glumes bilobed; [section Triplathera]
        5 Central awns of lemmas not flanked by membranous lobes; upper glumes not bilobed; [section Bouteloua]
          6 Plants clumping, with short, knotty rhizomes; culms in clumps
          6 Plants long-rhizomatous; culms solitary or incidentally close to one another
    3 Panicle branches persistent; disarticulation occurring above the glumes (the individual florets therefore falling); spikelets > 18 per branch, pectinately disposed; [native west of the Mississippi River, and in FL peninsula, otherwise rare introductions].
             7 Panicle branches extending beyond the base of the terminal spikelets 3-11 mm; [section Hirsuta; subsection Hirsuta]
             7 Panicle branches terminating in a spikelet.
               8 Spikes (2-) 4-6 (-10) per culm, each 8-26 mm long, with 22-52 spikelets per spike; [section Barbata]
               8 Spikes (1-) 2 (-6) per culm, each 15-60 mm long, with 40-100 or more spikelets per spike; [section Chondrosum]