Therapy derived from flower involving new team (9)
I believe the answer is:
treatment
'therapy' is the definition.
(I know that therapy can be written as treatment)
'flower involving new team' is the wordplay.
'flower' becomes 'trent' (River Trent).
'involving' indicates putting letters inside.
'new' indicates an anagram.
'team' with letters rearranged gives 'atme'.
'trent' placed around 'atme' is 'TREATMENT'.
'derived from' acts as a link.
(Other definitions for treatment that I've seen before include "Method of handling or healing" , "Medication" , "Discussion" , "See 41 Down" , "course of drugs" .)