Relating to the study of plants (7)
I believe the answer is:
botanic
'relating to the study of plants' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for botanic that I've seen before include "Relating to plant studies" , "Relating to the study of plants" , "linked to plants" , "Relating to plant study" , "Of gardens like Kew" .)