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Key J1: woody plants with opposite, simple, palmately or pinnately lobed leaves

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1 Leaves pinnately lobed.
  2 Leaves harshly scabrous on the upper surface; leaves typically a mix of alternate, opposite, and whorled
  2 Leaves glabrous or glabrescent on the upper surface; leaves strictly opposite
1 Leaves palmately lobed.
    3 Plants climbing by twining; stems with retrorse prickles; foliage scabrous
    3 Plants erect trees or shrubs; stems not prickly; foliage smooth or pubescent, but not scabrous.
      4 Leaves 3-9-lobed, the margins generally serrate or sublobed; fruit either a drupe or a schizocarp of 2 samaroid mericarps (maple “keys”).
        5 Fruit a schizocarp of 2 samaroid mericarps (maple “keys”); stamens (4-) 8 (-12); small to large trees; petioles >1× as long as the leaf blade
        5 Fruit a drupe; stamens 5; shrubs; petioles < ¾× as long as the leaf blade
      4 Leaves 3-lobed, the margins entire; fruit a capsule.
          6 Flowers white to yellow; capsules linear, >10× as long as wide; leaf undersurface with curly simple hairs; nectar glands present in the main vein axils on the undersurface of the leaf (visible from the underside or the upperside in fresh leaves and herbarium specimens)
          6 Flowers lavender; pods ellipsoid, < 2× as long as wide; leaf undersurface with branched (dendritic) stellate hairs; nectar glands absent

Key J2: woody angiosperms with opposite, simple leaves with toothed margins {add [Abelia] CAPRIFOLIACEAE}

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1 Leaves evergreen.
  2 Plant a shrub, erect, not requiring support.
    3 Leaves with spiny margins
    3 Leaves with crenate or serrate margins.
      4 Leaves slightly to strongly fleshy; inflorescence a head; [maritime situations]
 Iva
      4 Leaves not fleshy; inflorescence either a head or otherwise; [collectively widespread].
        5 Leaves > 8 cm long, typically spotted with yellow, coarsely toothed; fruit a red drupe; [commonly cultivated, rarely seeding down nearby]
        5 Leaves < 8 cm long, not yellow-spotted, serrulate; fruit a capsule or purplish drupe; [plants native or cultivated].
          6 Inflorescence a head; [s. FL]
          6 Inflorescence otherwise; [more widespread].
  2 Plant a subshrub, creeping shrub, or liana.
                 9 Leaves spinose-serrate; [aliens, rarely naturalized]
                 9 Leaves serrate (not spinose), serrulate, or crenate; [aliens and natives, collectively widespread].
                   10 Leaves slightly to strongly fleshy; inflorescence a head; [maritime situations]
 Iva
                   10 Leaves not fleshy; inflorescence otherwise; [collectively widespread].
                     11 Leaves on vigorous shoots with a few coarse rounded teeth towards the base (most leaves entire)
                     11 Leaves serrulate to serrate, the teeth uniformly around the margin or concentrated towards the tip; fruit dry, either indehiscent and 1-seeded or capsular and with several seeds.
                       12 Flowers 5-merous; petals fused; fruit indehiscent, 1-seeded; [montane, from e. TN, WV, and w. MD northwards in our area]
                       12 Flowers 4- or 5-merous; petals separate; fruit capsular, dehiscent, several-seeded; [collectively widespread in our area]
1 Leaves deciduous.
                          13 Leaves slightly to strongly fleshy; inflorescence a head, subtended by an involucre of phyllaries; [maritime situations]
 Iva
                          13 Leaves not fleshy; inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head subtended by bracts, but then with other features differing, such as stamens 4, or green calyx present, or petals separate, or fruit a schizocarp of mericarps, etc.); [collectively widespread].
                            14 Lianas climbing by twining or by adventitious roots.
                              15 Stems with retrorse prickles; foliage scabrous
                              15 Stems not prickly; foliage smooth to variously hairy, but not scabrous.
                                16 Leaves on vigorous shoots with a few coarse rounded teeth towards the base (most leaves entire), the larger leaves < 3 cm wide; lianas climbing by twining; fruit a fleshy berry; flowers 5-merous, with a fused, tubular corolla
                                16 Leaves serrate, the teeth towards the leaf apex, the larger leaves > 4 cm wide; lianas climbing by adventitious roots; fruit a capsule; flowers 7-10-merous, with separate petals
                            14 Upright shrubs or trees, lacking any adaptations for climbing.
                                  17 Trees; leaves often a mix of alternate and opposite.
                                    18 Leaves harshly scabrous on the upper surface; fruit a multiple of achenes; leaf venation pinnate but irregular
                                    18 Leaves not scabrous; fruit a 2-4-seeded drupe; leaf venation neatly pinnate, the lateral veins nearly straight and parallel to one another
                                  17 Shrubs or trees; leaves strictly opposite (or often a mix of alternate and opposite in RHAMNACEAE).
                                       19 Trees; leaves palmately-veined, with 5 or more veins from the base; [rarely naturalizing]
                                       19 Shrubs; leaves either triple-veined from near the base or pinnate-veined; [collectively widespread and common]
                                         20 Leaves strongly triple-veined from at or near the base of the blade, the 2 lateral veins arching towards the tip and rejoining the midvein or nearly so (becoming diffuse before rejoining); petals 4, white; stamens 15-90
                                         20 Leaves pinnate-veined; petals various, not both 4 and white (except sometimes in Hydrangea); stamens 1-15 (except 15-30 in Exochorda in ROSACEAE).
                                           21 Inflorescence head-like; flowers sympetalous and 4-lobed; fruit 2 seeded
                                           21 Inflorescence more diffuse, with internal axes and pedicels; flowers not both sympetalous and 4-lobed (except in Forsythia and Buddleja); fruit 1-seeded, 2-4-seeded, or 4-many-seeded.
                                               23 Corolla absent; flowers inconspicuous and small, in axillary fascicles or catkins.
                                                 24 Flowers in axillary fascicles; leaves strictly opposite (subopposite)
                                               23 Corolla present; flowers larger, in terminal cymes, corymbs, racemes, panicles, or in axillary cymes or fascicles.
                                                    25 Petals separate; stamens 8-10 (-60) (or 4-6 in RHAMNACEAE and Euonymus in CELASTRACEAE).
                                                      26 Flowers 1-few, in axillary cymes; stamens 4-6; stems brown, tan, gray, or green.
                                                        27 Leaf venation neatly pinnate, the lateral veins nearly straight and parallel to one another; stems brown, tan, or gray
                                                      26 Flowers 1 and terminal, or many, in terminal panicles or corymbs; stamens 8-10 (-60); stems brown, tan or gray.
                                                    25 Petals fused, at least basally, and often strongly tubular; stamens 2, 4, or 5.
                                                                 31 Stamens 2; petals yellow; flowers radially symmetrical; inflorescence an axillary fascicle
                                                                 31 Stamens 4; petals white, pink, or lavender; flowers bilabiate; inflorescence a terminal thyrse or panicle or an axillary cyme.
                                                                                  39 Inflorescence a catkin, the flowers small (< 5 mm in diameter) and tightly arranged on the inflorescence axis (>5 per cm of the axis)
                                                                                  39 Inflorescence various, but more diffuse, the flowers larger (> 5 mm in diameter, except for some flowers in Hydrangea in HYDRANGEACEAE) and loosely arranged (< 5 per cm of axis).