Choice in flower for supporter (7)
I believe the answer is:
devotee
'supporter' is the definition.
(I've seen this before)
'choice in flower' is the wordplay.
'choice' becomes 'vote' (vote is a kind of choice**).
'in' means one lot of letters goes inside another.
'flower' becomes 'dee' (River Dee).
'vote' inserted inside 'dee' is 'DEVOTEE'.
'for' is the link.
(Other definitions for devotee that I've seen before include "Fan, enthusiast" , "A very loyal or loving person" , "Zealous follower" , "Big fan" , "Ardent follower and admirer" .)