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Key to Senna

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1 Herbs, 0.5-22 dm tall.
  2 Leaves with 1 pair of leaflets; gland positioned at the single pair of leaflets; [TX and OK].
    3 Leaflets (1.3-) 1.4-3.7 (-4.1)× as long as wide; plants 1-3.5 dm tall; foliage cinereous, gray-green; [section Chamaefistula, series Brachycarpae].
      4 Leaflets 2-3.7 (-4.1)× as long as wide; hairs of the upper stem mostly 0.2-0.7 mm long
      4 Leaflets (1.3-) 1.4-1.8× as long as wide; hairs of the upper stem mostly 1-3 mm long; style 1-2 mm long, stout
    3 Leaflets (3.6-) 4-10× as long as wide; plants 0.4-7 dm tall; foliage glabrate to cinereous, green.
        5 pod 10-15 mm long; plants 0.4-1.2 (-1.7) dm tall; [section Chamaefistula, section Tharpia]
        5 pod (20-) 23-32 (-35) mm long; plants (1.5-) 2-7 dm tall; [section Chamaefistula, section Brachycarpae]
  2 Leaves with 3-14 pairs of leaflets; gland(s) either 0, or present and positioned variously (see below); [collectively widespread].
          6 Racemes spike-like, 3-6 (-10) dm long; legume 4-winged; glands 0; leaves with (6-) 7-14 pairs of leaflets; [section Senna, series Pictae]
          6 Racemes not spike-like, < 3 dm long; legume not winged; glands present on petiole or rachis of leaves; leaves with (3-) 4-9 (-10) pairs of leaflets.
             7 Leaves with 3 pairs of leaflets; leaflets obovate, 1.6-2.5× as long as wide, the widest point past the midpoint, the apex broadly rounded to obtuse; gland(s) positioned at the lowest pair of leaflets and sometimes also at the 2nd pair; [section Chamaefistula, section Trigonelloideae]
             7 Leaves with (3-) 4-9 (-10) pairs of leaflets; leaflets ovate, lanceolate, or elliptic, 1.9-7× as long as wide, the widest below or near the midpoint, the apex acuminate, acute, or obtuse; gland(s) positioned variously (see below).
               8 Glands on the rachis between each pair of leaflets except the uppermost; plants silvery-gray pubescent; [TX]; [section Chamaefistula, section Brachycarpae]
               8 Glands on the petiole below the 1st pair of leaflets (rarely at the summit of the petiole, in association with the 1st pair of leaflets); plants green, glabrous or relatively inconspicuously hairy; [collectively widespread].
image of plant
Show caption*© Mary Keim, some rights reserved (CC BY-NC-SA)
                 9 Gland cylindrical or conical; [section Chamaefistula, series Basiglandulosae]
                   10 Leaflets 1.5-3.0 cm wide, in 3-6 pairs; racemes with 1-5 flowers; [section Chamaefistula, series Basiglandulosae]
                   10 Leaflets 0.7-2.0 cm wide, in 6-10 pairs; racemes with 5-10 (-25) flowers; [section Chamaefistula, series Temperatae].
                     11 Legume 5.5-8 mm wide, with broad, nearly square segments, usually pilose initially, the hairs up to 0.8-2 mm long (sometimes glabrate); ovary lanate with hairs to 1 mm long; ovules 10-15 (-18); petiolar gland broadest above the middle
                     11 Legume 8-11 mm wide, with narrow segments (much shorter than broad), glabrous (or with a few hairs, these < 0.6 mm long); ovary strigulose with hairs to 0.5 mm long; ovules 20-25 (-30); petiolar gland usually broadest at or below the middle.
                       12 Leaflets acute to obtuse, 2-3× as long as wide, symmetrical or the terminal pair slightly falcate; [widespread in our area, south to Panhandle FL]
                       12 Leaflets acuminate, 3-7× as long as wide, at least the upper strongly falcate; [of peninsular FL]
1 Shrubs and trees, 20-200 dm tall.
                          13 Leaves with 5-16 (-18) pairs of leaflets.
                            14 Glands between the 1st pair of leaflets, and also sometimes between the 2nd to 3rd pairs.
                              15 Fertile stamens 7; flowers asymmetrical; [section Peiranisia, series Interglandulosae]
                              15 Fertile stamens 10; flowers bilaterally symmetrical; [section Psilorhegma]
                                16 Flowers asymmetrical; leaflets 3-4× as long as wide; [section Peiranisia, series Excelsae]
                                16 Flowers bilaterally symmetrical; leaflets 1.5-3.5 (-4)× as long as wide.
                                  17 Racemes spike-like, 3-6 (-10) dm long; fruit quadrangular in ×-section, 4-winged; [section Senna, series Pictae]
                                    18 Shrub; fruit 7-12 cm long, 1.7-2.3 cm wide; inflorescence racemose, cylindroid, the unopened flowers covered by broad brownish-black bracts; [section Senna, series Pictae]
                                    18 Tree; fruit (15) 20-30 cm long, 1.2-1.6 cm wide; inflorescence paniculate, initially corymbiform, the unopened flowers with small, inconspicuous bracts; [section Chamaefistula, series Floridae]
                          13 Leaves with (1-) 2-7 pairs of leaflets.
                                       19 Glands 0; tree; fruits 22-35 cm long; [section Peiranisia, series Isandrae]
                                       19 Glands present, at least between the 1st pair of leaflets; shrub to tree; fruits 6-18 cm long.
                                         20 Leaflets acuminate, the terminal pair 4.5-10.5 cm long; glands between all leaflet pairs except the terminal; [section Chamaefistula, series Colutoideae]
                                         20 Leaflets acute, obtuse, or rounded, the terminal pair 2.2-5.4 cm long; glands between the 1st pair (sometimes also the 2nd or rarely the 3rd pair as well).
                                           21 Fruits strongly flattened, the valves dehiscing and becoming stiffly papery in texture; seeds 2-8-4.5 mm long, 1.7-2.5 (-2.7) wide; [native of pine rocklands, dunes, etc. in s. FL]; [section Chamaefistula, section Basiglandulosae]
                                           21 Fruits cylindrical (reminiscent of a green bean), the valves dehiscing only tardily, remaining tough and thick in texture; seeds 3.9-6.0 (-6.6 mm long, (2.8-) 2.9-4.3 mm wide; [horticultural non-natives, persistent, weakly establishing near plantings, or naturalizing]; [section Chamaefistula, series Colutoideae]
                                             22 Leaflets acute, to obtuse or broadly rounded; larger leaflets (3.3) 3.5-5.6 (6.5)× as long as wide; fruits 7-12 cm long.
                                             22 Leaflets rounded or retuse at apex (sometimes with a mucro); larger leaflets 1.25-3.5 (-3.9)× as long as wide; fruits 8-18 cm long.
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