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Key to Bouteloua

Poaceae

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 Spikelets either solitary on panicle branches OR if branches each with 2+ spikelets then the first (proximal-most) spikelet on each branch with only 1 floret present; plants annuals (B. aristidoides) or tufted perennials (B. uniflora); [primarily natives of TX southward].
        5 Plants tufted annuals; spikelets 2 or more on panicle branches (although the first spikelet on each branch with only 1 floret); panicle branches 1-15; [section Hirsuta; subsection Eriopoda]
        5 Plants tufted perennials; spikelets solitary on panicle branches; panicle branches 15-70; [section Bouteloua]
      4 Spikelets never solitary on branches and all alike (each spikelet consisting of 1 bisexual and 1-2 rudimentary spikelets); the lowest spikelet on each branch never with only a single floret; plants perennial, variously tufted, stoloniferous or rhizomatous; [native species of limestone habitats, also with some introduced populations].
          6 Central awns of lemmas flanked by 2 membranous lobes (1-1.5 mm long); upper glumes bilobed (B. rigideiseta) or not (B. repens).
             7 Upper glumes bilobed (the awns arising from between the glume teeth); branch axes of the inflorescence with apices bifurcate to trifurcate; [section Triplathera]
             7 Upper glumes acute, unawned or awn-tipped (if the latter, the single awn ca. 1 mm long); branch axes of the inflorescence with apices entire; [section Triathera]
          6 Central awns of lemmas not flanked by membranous lobes; upper glumes not bilobed; [section Bouteloua].
               8 Glumes conspicuously pubescent throughout; [section Opizia]
               8 Glumes primarily glabrous, sometimes scabrous but lacking midvein pubescence (sometimes strigose in B. repens, if so the glume backs lacking pubescence).
                 9 Panicles 4-14 cm long, with (3-) 7-12 spreading to ascending spikelike branches; [section Triathera)
                 9 Panicles 13-30 cm long, with (12-) 30-80 conspicuously reflexed spikelike branches; [section Bouteloua].
                   10 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; [primarily natives west of the MS river and in FL peninsula (B. hirsuta), otherwise rare introductions northeastward].
                     11 Panicle branches extending beyond the base of the terminal spikelets (3-) 5-11 mm (the tips of the branches shortly exserted past the terminal spikelet); upper glumes of spikelets (at least some on a plant) with papillose-based hairs; [section Hirsuta; subsection Hirsuta].
                       12 Culms usually decumbent and branched from the base; rachilla segments subtending the 2nd florets lacking a distal tuft of hairs
                       12 Culms erect, usually unbranched from the base; rachilla segments subtending the 2nd florets with a distal tuft of hairs
                     11 Panicle branches terminating in a spikelet; upper glumes of spikelets variously glabrous to pubescent, if pubescent then the hairs not papillose-based (except sometimes in B. gracilis).
                          13 Lower culm internodes densely white-wooly pubescent; spikes each with 9-20 spikelets; [n. and c. TX only in our flora area]; [section Hirsuta]
                          13 Lower culm internodes glabrous to somewhat pubescent immediately below the nodes but not as above; spikes each with 22-100+ spikelets; [collectively widespread, including TX].
                            14 Spikes 1-3 (-6) per culm, each 15-60 (-75) mm long, with 40-100+ spikelets per spike; plants cespitose perennials, often with short, stout rhizomes; caryopses 2.5-3.0 mm long; [section Chondrosum]
                            14 Spikes (2-) 3-9 per culm, each 8-30 mm long, and with 20-52 spikelets per spike; plants either tufted annuals or rarely short-lived perennials (B. barbata) or cespitose perennials that occasionally produce short rhizomes (B. trifida); caryopses 0.8-1.5 mm long.
                              15 Central awns of the lemmas flanked by 2 membranous lobes; lowest lemmas densely pilose (the hairs spreading), each with awns 0.5-3 mm long; panicle branches each with 20-55 spikelets; [section Barbata]
                              15 Central awns of lemmas not flanked by 2 membranous lobes; lowest lemmas glabrous or if pubescent then the hairs appressed, each with awns 2.2-6.6 mm long; panicle branches each with 8-24 (-32) spikelets; caryopses 0.8-1.5; [section Trifida]