In overseas territories, it's a bloomer (5)
I believe the answer is:
aster
'bloomer' is the definition.
(aster is a kind of flowering plant)
'in overseas territories it's a' is the wordplay.
'in' indicates a hidden word.
'ASTER' can be found hidden inside 'overseas territories a'.
(Other definitions for aster that I've seen before include "Daisy-like plant" , "bloomer" , "Large daisy" , "Stare oddly at the flower" , "Flower of the daisy family - rates (anag)" .)