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Key to Vachellia

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image of plant
Show caption*© Keith Bradley
1 Pinna pairs 10-17 (-25) per leaf; leaflet pairs 20-30 per pinna
image of plant
Show caption*© Jay Horn
1 Pinna pairs 1-8 per leaf; leaflet pairs 2-20 pairs of leaflets.
  2 Nodal thorns basally expanded and fused, hollow.
    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]

Key to Fabaceae, Key B: woody legumes (trees, shrubs, or woody vines) with bipinnately compound leaves

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1 Leaves variously modified from strict 2-even-pinnateness, either with 1) a mixture (on a tree) of 1-even-pinnate and 2-even-pinnate leaves, and/or 2) the pinnae or leaflets often subopposite or fully alternate, and/or 3) with an odd number of pinnae per leaf (the tip of the rachis with a pair of lateral pinnae and a terminal pinna, but the leaflets of the pinnae still in opposite pairs), and/or 4) the basal pair of pinnae evolutionarily replaced by a single pair of leaflets larger than the other leaflets.
  2 Flowers small, inconspicuous, in catkin like-racemes or racemes of racemes; perianth greenish-white or greenish-yellow, with a cylindrical hypanthium to 10 mm long and shorter perianth lobes; flowers mostly unisexual; large trees; fruits woody and indehiscent at maturity, 1-5 cm wide[ collectively widespread in our region, but absent from s. FL and s. TX].
    3 Leaves characteristically a mixture (on a tree) of 1-even-pinnate (mainly on spurs) and 2-even-pinnate (mainly on new growth), the pinnae and the leaflets strictly opposite or subopposite; leaflets 1.5-4 cm long, acute to rounded at the apex; trunks with simple, trident, or multiply branched thorns to 20 cm long (or unarmed)
    3 Leaves all 2-even-pinnate, the basalmost "pinna pair" usually replaced by a pair of leaflets larger than the others, the pinnae and the leaflets often 'straying' to subopposite or fully alternate arrangement (some pinnae appearing odd-pinnate); leaflets 3-6 cm long, acuminate at the apex; trunks unarmed
  2 Flowers either with conspicuous petals or aggregated into spikes or spherical heads with showy stamens; petals either (Caesalpinoids) yellow, orange, red, or (Mimosoids) the tubular perianth whorls less conspicuous than the stamens, these yellow to orange; flowers bisexual; small shrubs, shrubs, small or medium trees, or large trees (if large trees, then of tropical parts of our region); fruits papery or chartaceous (rarely woody), often < 2 cm wide; [collectively widespread, including of s. FL and s. TX].
      4 Leaves with pinnae and leaflets mostly subopposite or fully alternate; [exotic, s. FL]; [Mimosoid]
      4 Leaves with an odd number of pinnae per leaf (the tip of the rachis with a pair of lateral pinnae and a terminal pinna), but the leaflets in opposite pairs; [native or exotic, TX and OK]; [Caesalpinoid].
        5 Shrub or small tree, 5-50 dm tall; sepals ovate; leaflets not glandular, or with glands only along the leaflet margin
        5 Sprawling shrub, less than 6 dm tall; sepals linear; leaflets glandular punctate across the lower surface (these orange in life, drying black)
1 Leaves strictly 2-even-pinnate (with pinna pairs borne opposite one another and no pinna terminal on the rachis, and with leaflets also born in opposite pairs).
          6 Pinna pairs 1-6 (-7) per leaf; leaflets 4-ca. 250 per leaf.
             7 Leaflets 1.5-14 mm long.
               8 Glands absent on petioles and rachises.
                 9 Shrub, small tree, or scrambling liana; branches armed with straight nodal spines or internodal catclaw prickles.
                   10 Branches armed with paired, straight, nodal spines, these simple or 3-branched; branches and larger stems green, photosynthetic; flowers caesalpinoid, 2-2.5 cm in diameter.
                   10 Branches armed with catclaw prickles scattered along internodes; branches and stems brown; flowers caesalpinoid or mimosoid.
                     11 Scrambling liana; flowers caesalpinoid, 1.5-2 cm across
                     11 Shrub; flowers mimosoid, aggregated into spherical inflorescences 9-15 mm in diameter
               8 Glands (stalked, columnar, or domed) 1 or more on petioles or rachises, on the petiole or at rachis nodes.
                          13 Stamens connate basally into a tube; spherical inflorescences whitish or cream, 15-23 mm in diameter
                          13 Stamens free; spherical inflorescences yellow, 6-8 mm in diameter
                       12 Branches armed with straight nodal spines or internodal catclaw prickles.
                            14 Branches armed with catclaw prickles scattered along internodes.
                              15 Leaflet pairs 6-25 per pinna; inflorescences spherical (or cylindrical in Prosopis laevigata).
                                    18 Shrub or small tree; pinna pairs 2-5 (-6) per leaf; leaflet pairs 9-20 per pinna; fruit flat, straight.
                                       19 Spherical inflorescences 15-23 mm in diameter; stamens connate basally into a tube; fruits flat, about 1 cm wide, 2-4 mm thick
                                       19 Spherical inflorescences 6-13 mm in diameter; stamens free; fruits turgid, cylindrical, about 1 cm in diameter (wide and thick)
             7 Leaflets 10-60 mm long (at least the larger leaflets on a plant > 14 mm long).
                                           21 Pinna pairs 1 per leaf; branches unarmed; flowers red-pink, mimosoid, aggregated into spherical inflorescences 5-7 cm in diameter
                                           21 Pinna pairs 2-5 per leaf; branches armed with catclaw prickles scattered along internodes; flowers yellow to orange, caesalpinoid, each flower 0.7-2 cm across.
                                         20 Glands (stalked, columnar, or domed) 1 or more on petioles or rachises, on the petiole or at rachis nodes.
          6 Pinna pairs 4-25 per leaf (at least the larger leaves on a plant with > 6 pinna pairs); leaflets 150-3000 per leaf.
                                                          28 Leaf rachis with cupular glands at nodes; flowers mimosoid, pink, aggregated into a spherical head 5-6 cm in diameter
                                                              30 Branches armed with catclaw prickles scattered along internodes; shrub; flowers mimosoid, white, cream, or pink, aggregated into spherical heads 0.9-2 cm in diameter.
                                                            29 Glands (stalked, columnar, or domed) or nonglandular spheroid projections 1 or more on petioles or rachises, on the petiole or at rachis nodes.
image of plant
Show caption*© Keith Bradley
                                                                   32 Fruits 30-60 cm long, woody, persistent and indehiscent on the tree; flowers caesalpinoid, scarlet and yellow, 8-10 cm across; rachis with spheroidal projections at the nodes; petiole lacking glands
                                                                   32 Fruits < 20 cm long, papery, coriaceous, or woody; flowers mimosoid, white, cream, pink, or pale yellow, aggregated into spherical heads 1-6 cm in diameter; rachis lacking spheroidal projections; petiole bearing domed or saucer-shaped glands along the petiole or at the 1st pair of pinnae.
                                                                              37 Branches armed with stout thorn spurs (these simple or branched); inflorescences cylindrical, bicolored, the base of pink or whitish staminodes, the tip of yellow stamens; fruits flattened, but also curved and contorted
                                                                              37 Branches armed with paired nodal spines, these either narrow and needle-like or massive, hollow, and with an entrance hole; fruits turgid, straight or slightly curved