Activist set on fire area in plant (8)
I believe the answer is:
militant
'activist' is the definition.
(I know that activist can be written as militant)
'set on fire area in plant' is the wordplay.
'set on fire area' becomes 'lita' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'plant' becomes 'mint' (mint is a kind of plant).
'lita' placed within 'mint' is 'MILITANT'.
Can you help me to learn more?
(Other definitions for militant that I've seen before include "Showing a fighting disposition" , "In mood for aggressive action" , "Bellicose" , "Warlike, combative" , "Aggressive, willing to fight" .)