I went by the quest rather smoothly, though I believe I might have had 4 different saplings? I'm not sure, could try that though see if it works.
I relaunched regrowth and reloaded my world and now have the following saplings in my immediate inventory:
Rainbow Eucalyptus Sapling x1 from ExtrabiomesXL
Cypress Sapling x1 from ExtrabiomesXL
Jungle Sapling x2 from Minecraft
Acacia Sapling x2 from Minecraft
Vermillion Autumn Sapling x2 from ExtrabiomesXL
Acacia Sapling x1 from ExtrabiomesXL
Japanese Maple Sapling x1 from ExtrabiomesXL
Hawthorn Sapling x1 from Witchery
Birch Sapling x1 from Minecraft
Sakura Sapling x1 from ExtrabiomesXL
Alder Sapling x1 from Witchery
Spruce Sapling x16 from Minecraft
Rowan Sapling x1 from Witchery
Bald Cypress Sapling x1 from ExtrabiomesXL
Citrine Autumn Sapling x1 from ExtrabiomesXL
Japanese Maple Shrub Sapling x1 from ExtrabiomesXL
Dark Oak Sapling x1 from Minecraft
Redwood Sapling x2 from ExtrabiomesXL
Fir Sapling x1 from ExtrabiomesXL
Oak Sapling x4 from Minecraft
Did I corrupt the questing data or something? Maybe I should backup my world and redownload???
Edit: somehow I must have corrupted the questing data without realizing it...
I backed up my worlds, re download regrowth 0.8.2 and restored my saves and launched minecraft. Now the quest book detects that I have four saplings.