Scientist who studies plants (8)
I believe the answer is:
botanist
'scientist who studies plants' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for botanist that I've seen before include "Expert in study of plants and trees" , "To sit ban out for expert in study of plants" , "One studying plants" , "Expert in plant biology" , "Expert on plant life" .)