Island gentleman brought back plant (4)
I believe the answer is:
iris
'plant' is the definition.
(type of flower)
'island gentleman brought back' is the wordplay.
'island' becomes 'i' (geographical abbreviation).
'gentleman' becomes 'sir' (a man may be addressed as sir).
'brought back' is a reversal indicator.
'sir' reversed gives 'ris'.
'i'+'ris'='IRIS'
(Other definitions for iris that I've seen before include "bit of a looker" , "Flag,flower and part of the eye" , "bloomer?" , "Fleur-de-lys" , "Flower - girl's name" .)