Of plants (7)
I believe the answer is:
botanic
'of plants' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for botanic that I've seen before include "Of gardens like Kew" , "linked to plants" , "Relating to plant science" , "Relating to plant study" , "Concerned with study of plants and trees, like famous Dublin Gardens" .)