It's about what's not right in various plants and trees (5)
I believe the answer is:
resin
'various plants and trees' is the definition.
I can't judge whether this defines the answer.
'it's about what's not right in' is the wordplay.
'it's about' shows that the letters should be reversed in order.
'what's not' becomes 'se' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'right' becomes 'r' (common abbreviation).
'se'+'r'='ser'
'ser' reversed gives 'res'.
'res'+'in'='RESIN'
Can you help me to learn more?
(Other definitions for resin that I've seen before include "Synthetic compound" , "It's obtained from tree-sap" , "Exudation from fir trees" , "eg Rosin" , "Substance from tree-sap" .)