Flora of the Southeastern United States

1 Woody vine, climbing by adventitious roots; petals 7-10; [subgenus Decumaria, section Decumaria; or genus Decumaria]

1 Shrub; petals 4-5.

  2 Leaves unlobed, merely toothed; inflorescence a corymb (except H. paniculata); large sterile flowers absent to relatively few (0-15 per inflorescence), borne around the periphery of the corymb (except H. paniculata).

    3 Inflorescence a panicle; large sterile flowers many (> 20 per inflorescence), borne throughout the inflorescence; [large shrub to small tree, to 8 m tall and 10 cm trunk diameter]; [exotic, cultivated and sometimes persistent]; [subgenus Heteromallae, section Heteromallae; or genus Heteromalla]

    3 Inflorescence a corymb; large sterile flowers absent to relatively few (0-15 per inflorescence), borne around the periphery of the corymb; [small to medium shrub, to 3 m tall and 2 cm trunk diameter]; [native]; [subgenus Hydrangea, section Hydrangea; or genus Hydrangea s.s.].

      4 Lower leaf surface glabrous or inconspicuously puberulent, appearing green; trichomes of the lower leaf surface restricted to the midrib and major veins; sterile flowers absent, or, if present, usually < 1 cm in diameter

      4 Lower leaf surface variously pubescent, appearing white or gray; trichomes of the lower leaf surface on veins and interveinal areas; sterile flowers usually present, large and showy, usually greater than 1 cm in diameter.

        5 Lower leaf surface velutinous, pilose, or tomentose, appearing gray; trichomes usually not dense enough to entirely mask the green leaf surface; trichomes with prominent tubercles (as seen at 40× magnification); sterile flowers generally very few (0-3 per inflorescence)

        5 Lower leaf surface densely floccose-velutinous, felt-like, appearing bright white or silver; trichomes dense enough to entirely mask the green leaf surface; trichomes without tubercles, or with small and inconspicuous tubercles (as seen at 40× magnification); sterile flowers generally fairly many (2-15 per inflorescence)

1 Leaves pinnately lobed.

  2 Leaves harshly scabrous on the upper surface; leaves typically a mix of alternate, opposite, and whorled

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