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Key to Vachellia

Fabaceae

Vachellia

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1 Pinna pairs 10-17 (-25) per leaf; leaflet pairs 20-30 per pinna
1 Pinna pairs 1-8 per leaf; leaflet pairs 2-20 per pinna.
  2 Nodal thorns basally expanded and fused, hollow; [non-native species of the FL peninsula].
    3 Inflorescence cylindrical, 3× or more as long as wide; lower leaflet surface with 2-3 veins from the base and also obvious lateral veins
    3 Inflorescence spherical or slightly longer than the diameter, 1-2× as long as wide; lower leaflet surface with only the midvein visible
  2 Nodal thorns solid, separate (or fused in V. tortuosa).
      4 Leaflets 10-20 mm long; fruit laterally compressed
      4 Leaflets 1.5-6 mm long; fruit terete or nearly so.
        5 Pinna pair 1 per leaf; leaflet pairs 2-3 (-4) per pinna; leaflets 6-12 mm long; inflorescence cylindrical, cream
        5 Pinna pairs 2-8 per leaf; leaflet pairs 6-20 per pinna; leaflets 1-6 mm long; inflorescence spherical, yellow to orange
          6 Leaves with 4-8 pairs of pinnae; each pinna with 15-20 pairs of leaflets; petiolar gland elliptic; stipular spines often basally fused; leaflets reticulate below
          6 Leaves with 2-4 (-7) pairs of pinnae; each pinna with 9-20 pairs of leaflets; petiolar gland circular; stipular spines not basally fused; leaflets with or without apparent secondary venation, but not reticulate.
             7 Peduncle with bracts near the midpoint (or a nodal bump visible if they have fallen)
             7 Peduncle lacking bracts or with bracts immediately subtending the head.
               8 Mature leaflets 4-5 (-6) mm long, with secondary veins apparent on the lower surface; [in our area from e. GA south through FL peninsula]
               8 Mature leaflets 1.5-4 (-5) mm long, with secondary veins not apparent on the lower surface; [FL peninsula and panhandle west to TX and beyond]
                 9 Mature leaflets 2.5-4 (-5) mm long; petiole usually pubescent; peduncles lacking glands; [FL panhandle west to TX and beyond]
                 9 Mature leaflets 1.5-3.5 mm long; petiole glabrous; peduncles with tiny, red glands (use 10× magnification) (these deciduous and absent as the peduncle ages); [FL peninsula or s. TX]
                   10 Mature leaflets ca. 3 mm long; fruit valves velvety pubescent when young, becoming glabrescent; [s. TX]
                   10 Mature leaflets ca. 2 mm long; fruit valves glabrous; [FL]