Flora of the Southeastern United States
2022 Edition

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Click the number at the start of a key lead to highlight both that lead and its corresponding lead. Click again to show only the two highlighted leads. Click a third time to return to the full key with the selected leads still highlighted.

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Keyed in multiple places:

Key to Hydrangeaceae

1 Woody vine, climbing by aerial rootlets; petals 7-10; [tribe Hydrangeae]
1 Shrub; petals 4-5 (rarely 10 or many in the cultivars of Deutzia and Philadelphus).
..2 Pubescence of leaves and twigs stellate; stamens 10; [a cultivated alien, rarely escaped]; [tribe Philadelpheae]
..2 Pubescence of leaves and twigs simple; stamens 8-10 (Hydrangea) or 25-90 (Philadelphus); [natives and aliens].
....3 Leaf blades 10-30 cm long; inflorescences of 25-many flowers; stamens 8-10; [tribe Hydrangeae]
....3 Leaf blades 3-8 cm long; inflorescences of 1-7 flowers; stamens 25-90; [tribe Philadelpheae]

Key to Hydrangea

1 Woody vine, climbing by adventitious roots; petals 7-10; [section Decumaria of clade Hydrangea I; or genus Decumaria]
1 Shrub; petals 4-5.
..2 Leaves pinnately lobed, the lobes toothed; inflorescence a panicle; large sterile flowers many (> 20 per inflorescence), borne throughout the inflorescence; [section undetermined (“incertae sedis) of clade Hydrangea I; or genus Hydrangea s.s.]
..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]; [alien, cultivated and sometimes persistent]; [section Heteromallae of clade Hydrangea I; 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]; [section Hydrangea of clade Hydrangea I; 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)