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Keyed in multiple places:

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Key to Cannabaceae

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1 Tree or shrub; leaves simple and unlobed.
  2 Leaves glabrous beneath or sparsely pubescent; inflorescence of a solitary or a few flowers; leaf margins entire to rather irregularly serrate or dentate
  2 Leaves distinctly pubescent beneath; inflorescence a branched cyme, of 12-20 flowers; leaf margin finely and evenly serrulate
1 Herb or vine; leaves either compound or lobed.
    3 Erect herb; leaves with 3-7 leaflets
    3 Climbing or sprawling vine; leaves simple, with 1-9 lobes

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].
             7 Corolla tubular, campanulate, bilaterally symmetrical; fruit a 1-seeded achene (rarely produced)
             7 Corolla radially symmetrical, with 4-5 distinct petals; fruit a 2-10-seeded capsule or drupe.
               8 Fruit a 4-5-locular capsule, with 2 seeds per locule (though often fewer by abortion)
               8 Fruit a (2-) 3-locular, purplish-black drupe, with (2-) 3 single-seeded stones
  2 Plant a subshrub, creeping shrub, or liana.
                 9 Leaves spinose-serrate; [exotics, rarely naturalized]
                 9 Leaves serrate (not spinose), serrulate, or crenate; [exotics 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 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.
                                             22 Plants in flower.
                                               23 Corolla absent; flowers inconspicuous and small, in axillary fascicles or catkins.
                                                 24 Flowers in catkins; leaves usually a mix of opposite and alternate
                                                 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 pinnate, but irregular and reticulated; stems 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.
                                                          28 Inflorescence a solitary, terminal flower; stamens 30-60
                                                          28 Inflorescence a terminal panicle or corymb; stamens 8-15
                                                    25 Petals fused, at least basally, and often strongly tubular; stamens 2, 4, or 5.
                                                            29 Stamens 5.
                                                              30 Petals white, fused basally only, the lobes spreading
                                                              30 Petals pink, yellow, or reddish, fused for most of their length
                                                            29 Stamens 2 or 4.
                                                                 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.
                                                                   32 Petals 4; inflorescence a terminal thyrse
                                                                   32 Petals 5; inflorescence a terminal panicle or an axillary cyme.
                                                                     33 Inflorescence an axillary cyme
                                                                     33 Inflorescence a terminal panicle
                                             22 Plants in fruit.
                                                                       34 Fruit a berry, drupe, or achene, indehiscent, fleshy at maturity (or dry in Kolkwitzia).
                                                                         35 Fruit a berry, with 20+ seeds
                                                                         35 Fruit a drupe or achene, with 1-4 seeds.
                                                                           36 Fruit an achene (1-seeded), dry at maturity
                                                                           36 Fruit a drupe (1-4-seeded), fleshy at maturity.
                                                                              37 Inflorescence a terminal corymb
                                                                              37 Inflorescence axillary, fascicled or a cyme.
                                                                                38 Foliage with stellate hairs; fruit a pink-purple 4-seeded drupe
                                                                                38 Foliage glabrous or with simple hairs; fruit a dark red, black, or blue 1-4-seeded drupe.
                                                                                  39 Fruit a 1-seeded drupe; [NC southwards and westwards]
                                                                                  39 Fruit a 2-4-seeded drupe; [widespread in our region]
                                                                       34 Fruit a capsule, dehiscent, dry at maturity.
                                                                                    40 Inflorescence a catkin, the flowers small (< 5 mm in diameter) and tightly arranged on the inflorescence axis (> 5 per cm of the axis)
                                                                                    40 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).
                                                                                      41 Capsule prominently 5-angled (star-shaped in ×-section)
                                                                                      41 Capsule not angled.
                                                                                        42 Inflorescence axillary, fascicled.
                                                                                           43 Capsule pink to red; fruits solitary or in axillary cymes
                                                                                           43 Capsule brown; fruits in axillary fascicles
                                                                                        42 Inflorescence terminal, a raceme, panicle, corymb, or compound cyme or thyrse.
                                                                                             44 Inflorescence a flat-topped corymb or rounded compound cyme, as wide as or wider than long
                                                                                             44 Inflorescence elongated, a raceme, panicle, or thyrse, much longer than wide.
                                                                                               45 Capsule elongate (> 3× as long as wide), 8-25 mm long
                                                                                               45 Capsule about as long as wide, 3-6 mm long.
                                                                                                 46 Sepal lobes 5
                                                                                                 46 Sepal lobes 4

Key P2: herbaceous dicots with alternate, simple, and palmately lobed leaves on the stem

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1 Inflorescence an involucrate head subtended by phyllaries, the heads solitary or many and variously arrayed in secondary inflorescences, the ovary inferior, the corolla connate and tubular at least basally, the calyx absent, the stamens 5, the fruit a cypsela
1 Inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head, e.g. Eryngium in APIACEAE, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).
  2 Plant a vine, climbing by tendrils or twining.
    3 Vine climbing by twining.
      4 Leaf margins entire; flowers bisexual; plants hermaphroditic; petals connate, large and showy
      4 Leaf margins serrate; flowers unisexual; plants dioecious; petals absent
    3 Vine climbing by tendrils.
        5 Ovary inferior; petals connate; flowers unisexual
        5 Ovary superior; petals distinct; flowers bisexual
  2 Plant an herb, sometimes sprawling, reclining (e.g. Cymbalaria in PLANTAGINACEAE, Aconitum in RANUNCULACEAE), but lacking climbing adaptations such as tendrils or twining stems.
          6 Ovary inferior; inflorescence an umbel; fruit a schizocarp of 2 mericarps
             7 Involucre well-developed and obvious
             7 Involucre absent or minute
          6 Ovary superior; inflorescence various, not an umbel; fruit various, a capsule, an aggregate of achenes or follicles, a ring of (>2) mericarps.
               8 Perianth uniseriate, the corolla absent (the calyx petaloid and white in Cnidoscolus); flowers unisexual; plants either with stinging hairs or not
               8 Perianth biseriate (uniseriate in Aphanes in ROSACEAE and in Trautvetteria in RANUNCULACEAE); flowers bisexual; plants lacking stinging hairs.
                 9 Pistils many (or 2-3 in Aphanes in ROSACEAE), each with 1 carpel, arranged spirally or in a ring (if in a ring, of 2-5); fruit an aggregate of achenes, follicles, or utricles.
                   10 Perianth bilaterally symmetrical, either hooded or spurred; fruit an aggregate of follicles
                   10 Perianth radially symmetrical, not hooded or spurred; fruit an aggregate of utricles or achenes (plumose achenes in Geum)
                     11 Stamens showy, bright white, dilated towards the tip; pistils ca. 15; fruit an aggregate of utricles
                     11 Stamens not showy, white, or dilated towards the tip; pistils many (> 25); fruit an aggregate of achenes.
                       12 Flowers lacking a hypanthium; achenes short-beaked
                       12 Flowers with a prominent hypanthium; achenes with an elongate, plumose beak
                 9 Pistil 1, with 1-to many carpels (in many MALVACEAE, the carpels loosely united in a ring of more than 5 around the style); fruit a capsule, an achene, a follicle, or a ring of 3 or 5-many 1-seeded mericarps.
                          13 Perianth uniseriate, the corolla absent
                          13 Perianth biseriate, with well-developed and differentiated calyx and corolla
                            14 Corolla bilaterally symmetrical, the petals connate (except distinct in Delphinium in RANUNCULACEAE); fruit a capsule, a follicle, or a schizocarp of 3 1-seeded mericarps.
                              15 Corolla not spurred; fruit an elongate (10-20 cm) capsule with 2 curved beaks
                              15 Corolla with a nectar spur; fruit < 3 cm long.
                                16 Petals distinct; fruit a follicle
                                16 Petals connate; fruit a capsule or a schizocarp of 3 1-seeded mericarps.
                                  17 Carpels 2; fruit a capsule; stamens 4
                                  17 Carpels 3; fruit a schizocarp of 3 1-seeded mericarps; stamens 8
                            14 Corolla radially symmetrical, the petals distinct (fused and tubular in Ipomoea); fruit a capsule or a schizocarp consisting of a ring of 5-many 1-seeded mericarps.
                                    18 Stem trailing; petals fused and tubular
                                    18 Stem erect; petals separate.
                                       19 Stamens many, connate into a stamen tube; carpels 5-many, completely or only loosely fused; fruit a capsule or a schizocarp of 5-many mericarps borne in a ring; calyx often subtended by an epicalyx (an additional calyx-like, green, foliaceous whorl of bracts)
                                       19 Stamens 5 or 10, distinct; carpels 2 or 5, fused; fruit a capsule or a schizocarp of 5 1-seeded mericarps.
                                         20 Fruit a schizocarp of 5 1-seeded mericarps; carpels 5; stamens 10
                                         20 Fruit a capsule with 2 locules, loculicidal; carpels 2; stamens 5