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Key to Paspalum

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1 Both lower and upper glumes absent, or upper glume present on terminal spikelet only of a panicle branch.
  2 Plants stoloniferous; culms to 40 cm long; blades to 4 mm wide; spikelets 3.8-5.2 mm long, apex acuminate; upper glume sometimes present on terminal spikelet of a panicle branch
  2 Plants cespitose; culms to 200 cm long; blades to 35 mm wide; spikelets 1.8-2 mm long, apex obtuse; both glumes absent from all spikelets
1 At least upper glume present on all spikelets.
    3 Spikelets solitary, not associated with rudimentary spikelets or naked pedicels.
      4 Panicles usually composed of a terminal pair of branches, sometimes with 1 (-5) additional branches below the terminal pair.
        5 Upper glumes pubescent on the back or margins.
          6 Spikelets 1.3-1.9 mm long; upper glumes pilose along the margins; ligules 0.5-0.8 mm long; panicle branch axis 0.2-0.8 mm wide
          6 Spikelets 2.4-3.2 mm long; upper glumes sparsely pubescent on the back; ligules 1-2 mm long; panicle branch axis 1.2-2.2 mm wide
        5 Upper glumes glabrous.
             7 Spikelets elliptic, the tip acute or acuminate.
               8 Plants short-rhizomatous, culms appearing cespitose; blades to 4 mm wide; spikelets 3-3.6 mm long; lower lemmas 5-veined; upper florets stramineous to golden brown; most frequently found along roadsides and in pastures
               8 Plants rhizomatous, the culms separate; blades to 8 mm wide; spikelets 3-4.5 mm long; lower lemmas 3-veined; upper florets white; most frequently found in brackish and salt marshes
             7 Spikelets ovate to broadly elliptic, the tip obtuse to broadly acute.
                 9 Culms to 60 cm long; blades flat; panicle branches to 6.4 cm long; spikelets 1.9-2.3 mm long, 1.2-2 mm wide; upper glumes 3-veined
                 9 Culms to 120 cm long; blades flat or longitudinally folded; panicle branches to 15 cm long; spikelets 2.5-4 mm long, 2-2.8 mm wide; upper glumes 5-veined
      4 Panicles with 1-70 branches; if > 1, the branches arranged racemosely, the 2 uppermost not paired.
                   10 Panicle branches 7-70, the axes extending beyond the outermost spikelets; panicle branches disarticulating at maturity
                   10 Panicle branches 1-6, terminating in a spikelet; panicle branches persistent.
                     11 Upper florets olive to dark brown
                     11 Upper florets pale to tan.
                       12 Axes of panicle branches not broadly winged, 0.6-1.3 mm wide.
                          13 Spikelets orbicular, 2.8-3.2 mm wide
                          13 Spikelets slightly longer than broad, 2.0-2.5 mm wide
                       12 Axes of panicle branches broadly winged, 1.8-3.3 mm wide.
                            14 Culms to 100 cm long; spikelets 3.2-4 mm long, 1.6-1.7 mm wide; upper lemmas with a few short hairs at their tips; caryopses 2-3 mm long
                            14 Culms to 50 cm long; spikelets 1.7-2.1 mm long 1.1-1.4 mm wide; upper lemmas glabrous; caryopses 1-1.3 mm long
    3 Spikelets paired, or at least the second nonfunctional spikelet represented by a naked pedicel.
                              15 Spikelets 1.0-1.3 mm long
                                16 Nodes glabrous; blades 1.9-8 mm wide; panicle branches 2-6; upper florets 0.8-1.1 mm long
                                16 Nodes pubescent; blades 10-24 mm wide; panicle branches 18-50; upper florets 1.1-1.3 mm long
                              15 Spikelets 1.3-4.1 mm long.
                                  17 Margins of upper glumes and lower lemmas fimbriate, or ciliate with soft hairs 5 mm or more long.
                                    18 Culms to 70 cm long; upper glumes and lower lemmas broadly winged, the wing fimbriate; spikelets 2.4-3 mm wide
                                    18 Culms to 220 cm long; margins of upper glume and lower lemmas long-ciliate, wingless; spikelets 1.1-2.5 mm wide.
                                       19 Panicle branches 2-7; spikelets 2.3-4.0 mm long, 1.7-2.5 mm wide
                                       19 Panicle branches (4-) 10-30; spikelets 1.8-2.8 mm long, 1.1-1.5 mm wide
                                  17 Margins of upper glumes and lower lemmas glabrous or pubescent, but not winged, fimbriate, or long-ciliate.
                                         20 Upper florets olive to dark brown.
                                           21 Plants aquatic AND culms decumbent; lower glumes often present
                                           21 Plants either not aquatic OR if aquatic then with erect culms; lower glumes absent.
                                             22 Panicle branches 10-28 (occasionally more).
                                               23 Plants annual; axes of panicle branches broadly winged, the wings about as wide as the central portion; [common native]
                                               23 Plants perennial; axes of panicle branches narrowly winged, the wings narrower than the central portion; [rare exotics].
                                                 24 Blades 7-18 mm wide; axes of panicle branches 0.5-1.2 mm wide; spikelets 1.1-1.8 mm wide; upper florets 1.8-2.2 mm long
                                                 24 Blades 10-30 mm wide; axes of panicle branches 1-1.7 mm wide; spikelets 1.8-2.4 mm wide; upper florets 2.5-2.7 mm long
                                             22 Panicle branches 1-10.
                                                    25 Upper glumes glabrous.
                                                      26 Blades to 15 mm wide; panicle branches 1-10 (-28); branch axes 0.7-2.3 mm wide; spikelets 2-2.2 mm long
                                                      26 Blades to 7 mm wide; panicle branches 2-8; branch axes 0.6-1.1 mm wide; spikelets 2.2-3 mm long.
                                                        27 Panicle branches 2-7, 1.6-7.1 cm long; spikelets 2.5-3 mm long, 1.5-2.2 mm wide; upper florets dark brown
                                                        27 Panicle branches 5-8, 3.5-11 cm long; spikelets 2.2-2.7 mm long, 1-1.4 mm wide; upper florets chestnut brown
                                                    25 Upper glumes pubescent.
                                                          28 Rhizomes 5-25 cm long; ligule 1.2-1.5 mm long; panicle branches to 5.2 cm long; mature lower lemma transversely rugose
                                                          28 Rhizomes indistinct or absent; ligule 1-4.1 mm long; panicle branches to 11 cm long; mature lower lemma not transversely rugose.
                                                            29 Ligules 1-2 mm long; panicle branches 4-13, 6-11 cm long; spikelets 1.1-1.8 mm wide
                                                            29 Ligules 2-4.1 mm long; panicle branches 1-7, 1.1-7.1 cm long; spikelets 1.5-2.4 mm wide.
                                                              30 Plants annual; culms to 53 cm long; blades to 12 mm wide, flat; ligules 2-4.1 mm long; branch axes 0.8-1.3 mm wide; spikelets 2.1-2.6 mm long
                                                              30 Plants perennial; culms to 110 cm long; blades to 5.4 mm wide, usually conduplicate; ligules 2-3 mm long; branch axes 0.6-1.1 mm wide; spikelets 2.5-3 mm long
                                         20 Upper florets white, stramineous, or golden brown.
                                                                 31 Panicle with 15-100 branches.
                                                                   32 Plants annual; ligules 0.1-0.3 mm long; blades to 13 cm long; panicle branches to 2.5 cm long; upper glumes and lower lemmas rugose
                                                                   32 Plants perennial; ligules 1-6.3 mm long; blades to 62 cm long; panicle branches to 13 cm long; upper glumes and lower lemmas smooth.
                                                                     33 Plants rhizomatous; nodes and sheaths glabrous; panicle branch axes 0.9-1.2 mm wide
                                                                     33 Plants cespitose; nodes and sheaths pubescent; panicle branch axes 0.3-0.6 mm wide.
                                                                       34 Culms to 400 cm long; blades 10-23 mm wide; panicle branches 5-13 cm long, spreading to reflexed; spikelets 1.8-1.9 mm wide
                                                                       34 Culms to 180 cm long; blades 4.9-6.1 mm wide; panicle branches 1.2-8.5 cm long, erect to ascending; spikelets 0.9-1.3 mm wide
                                                                 31 Panicles with 1-15 branches.
                                                                         35 Spikelets 1.3-2.5 mm long.
                                                                           36 Upper glumes and often lower lemmas shortly pubescent.
                                                                              37 Lower glumes present
                                                                              37 Lower glumes absent.
                                                                                38 Panicles both terminal and axillary, the axillary panicles partially or completely enclosed by the subtending leaf sheath
                                                                                38 Panicles all terminal
                                                                           36 Upper glumes and lower lemmas glabrous.
                                                                                  39 Panicles both terminal and axillary, the axillary panicles partially or completely enclosed by the subtending leaf sheath
                                                                                  39 Panicles all terminal.
                                                                                    40 Ligules 0.2-0.4 mm long; branch axes 0.2-0.5 mm wide; spikelets 1.3-2 mm long, 0.7-1 mm wide
                                                                                    40 Ligules 0.5-4.7 mm long; branch axes 0.3-2 mm wide; spikelets 1.6-3.1 mm long, 1-2.8 mm wide.
                                                                                      41 Ligules 0.5-2.9 mm long; branch axes 0.4-2 mm wide, narrowly winged or wingless.
                                                                                        42 Spikelets 2-2.8 mm wide, orbicular to suborbicular.
                                                                                           43 Lower sheaths villous or hirsute; spikelets 2.6-3.5 mm long
                                                                                           43 Lower sheaths glabrous or sparsely papillose-pubescent; spikelets 2.2-2.8 mm long
                                                                                        42 Spikelets 1-1.9 mm wide, elliptic, ovate, or obovate.
                                                                                             44 Spikelets 1.6-2.2 mm long, 1.1-1.3 mm wide
                                                                                             44 Spikelets 2.1-3.7 mm long, 1-1.9 mm wide.
                                                                                               45 Blades 0.2-2 (rarely -8) mm wide; panicle branch axes 0.5-1.2 mm wide; spikelets 2.3-3.7 mm long, 1.3-1.9 mm wide
                                                                                               45 Blades 3-7 mm wide; panicle branch axes 0.3-0.8 mm wide; spikelets 2.2-2.5 mm long, 1-1.3 mm wide
                                                                         35 Spikelets 2.5-4.1 mm long.
                                                                                                 46 Spikelet pairs hardly imbricate, irregularly approximate, with evident gaps between groups of spikelets on the branches; lower glumes usually present; upper glumes (6-) 7-veined
                                                                                                 46 Spikelet pairs imbricate; lower glumes absent or present; upper glumes 1-5-veined.
                                                                                                   47 Upper glumes and lower lemmas pubescent (sparsely so, if at all, in P. pubiflorum).
                                                                                                     48 Panicle branches 1-4; branch axes 0.2-1 mm wide; spikelets 1.3-1.6 mm wide; lower glumes present
                                                                                                     48 Panicle branches 4-9; branch axes 1.1-2.3 mm wide; spikelets 1.5-2 mm wide; lower glumes absent.
                                                                                                        49 Blades 2-5 mm wide; branches ascending to erect; branch axes 1.2-1.5 mm wide; spikelets 2.8-3 mm long, 1.5-1.6 mm wide
                                                                                                        49 Blades 4-18 mm wide; branches ascending to spreading; branch axes 1.1-2.3 mm wide; spikelets 2.8-3.6 mm long, 1.5-2 mm wide.
                                                                                                          50 Blades becoming narrow basally; spikelets glabrous
                                                                                                          50 Blades rounded basally; spikelets pubescent
                                                                                                   47 Upper glumes and lower lemmas glabrous (sometimes sparsely pubescent in P. pubiflorum).
                                                                                                            51 Plants decumbent or cespitose, non-rhizomatous.
                                                                                                              52 Plants aquatic; blades to 10 mm wide; panicle branches ascending to erect, to 12 cm long; spikelets 2.5-3 mm long, 1.3-1.6 mm wide; lower glumes often present; upper glumes and lower lemmas with 5 veins
                                                                                                              52 Plants terrestrial; blades to 18 mm wide; panicle branches ascending to spreading, to 7.9 cm long; spikelets 2.8-3.6 mm long, 1.5-2 mm wide; lower glumes absent; upper glumes and lower lemmas with 3 veins.
                                                                                                                53 Blades narrowing basally; spikelets glabrous
                                                                                                                53 Blades rounded basally; spikelets pubescent
                                                                                                            51 Plants rhizomatous (shortly so in Paspalum praecox).
                                                                                                                  54 Blades 0.2-2 (-8) mm wide, involute; panicle branches 1-3; upper glumes 1-veined
                                                                                                                  54 Blades 2.2-18 mm wide, flat to folded; panicle branches 1-10; upper glumes 3-5-veined.
                                                                                                                     55 Ligules to 3.3 mm long; blades to 18 mm wide; spikelets 2.9-4.1 mm long; upper glumes 5-veined; upper florets golden brown
                                                                                                                     55 Ligules to 2.2 mm long; blades to 8.3 mm wide; spikelets 2.1-3.1 mm long; upper glumes 3-veined; upper florets white, straminous, light yellow or golden brown.
                                                                                                                       56 Blades 3-4 mm wide, flat; panicle branches 1-3, erect, 7-15 cm long; spikelets 2.7-3 mm long, 1.4-2 mm wide
                                                                                                                       56 Blades 2.2-8.3 mm wide, folded to flat; panicle branches 2-10, ascending to spreading, 0.8-10.3 cm long; spikelets 2.1-3.1 mm long, 2-2.8 mm wide.
                                                                                                                         57 Lower sheaths villous or hirsute; spikelets 2.6-3.5 mm long
                                                                                                                         57 Lower sheaths glabrous or sparsely papillose-pubescent; spikelets 2.2-2.8 mm long