Copyright 1998. Taxonomic Computer Research. All Rights Reserved.
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1. Plants scandent (vining) & ovary always inferior.....2
1. Plants erect (shrubby) & ovary inferior or superior.....10
2. leaves evergreen, only fertile flowers exist.....3
2. leaves deciduous, fertile & sterile flowers occur.....4
3. POSSIBLE ID=Hydrangea serratifolia
4. stamens 9 - 15 (uncommon in gardens).....5
4. stamens 15 - 20 (common garden form).....6
5. POSSIBLE ID=Hydrangea anomala subsp. anomala
5. POSSIBLE ID=Hydrangea anomala subsp. petiolaris
10. inflorescence an erect or conical cluster.....11
10. inflorescence a flat-topped cluster.....20
11. leaves pinnately lobed & ovary inferior.....12
11. leaves unlobed & ovary half-inferior.....13
12. POSSIBLE ID=Hydrangea quercifolia & cultivars
13. POSSIBLE ID=Hydrangea paniculata
20. ovary inferior in fruit and flower.....21
20. ovary half-inferior in both flower & fruit.....40
20. ovary inferior in flower & half-inferior in fruit.....50
21. bract broadly ovate to orbicular & capsules pubescent.....22
21. bract lanceolate to narrowly ovate & capsule glabrous.....23
22. POSSIBLE ID=Hydrangea involucrata
23. fertile flowers blue, densely hirsute.....24
23. fertile flowers white, hairs scattered.....30
24. velutinous & fleshy trichomes, lvs. 15 - 25 cm wide.....25
24. velutinous & strigose below , lvs. 5 - 35 cm wide.....26
24. velutinous , lvs. 9 - 25 cm wide.....27
25. POSSIBLE ID=Hydrangea aspera subsp. sargentiana
26. petioles 5 to 17 cm long, ovate to broadly ovate.....28
26. petioles 1 to 5 cm long, lanceolate to narrowly ovate.....29
28. POSSIBLE ID=Hydrangea aspera subsp. robusta
29. POSSIBLE ID=Hydrangea aspera subsp. strigosa
27. POSSIBLE ID=Hydrangea aspera subsp. aspera
30. leaves green & glabrous below except on midrib below.....31
30. leaves grey & densely pubescent below.....32
30. leaves white & densely tomentose below.....33
33. POSSIBLE ID=Hydrangea arborescens subsp. radiata
31. POSSIBLE ID=Hydrangea arborescens subsp. arborescens
32. POSSIBLE ID=Hydrangea arborescens subsp. discolor
40. POSSIBLE ID=Hydrangea heteromalla
50. petals 3-4 mm, capsules 6-8 mm; leaves glabrous, glossy.....51
50. petals 2-3 mm, capsules 3-6 mm; leaves pubescent, dull .....52
51. POSSIBLE ID=Hydrangea macrophylla subsp. macrophylla
52. POSSIBLE ID=Hydrangea macrophylla subsp. serrata
51. all flowers sterile.....53
51. flowers both sterile and fertile in 1 inflorescence.....54
53. POSSIBLE ID=Hydrangea macrophylla subsp. macrophylla f. macrophylla
54. POSSIBLE ID=Hydrangea macrophylla subsp. macrophylla f. normalis