Such a reversal — a bird in the bush (8)
I believe the answer is:
hibiscus
'bush' is the definition.
(hibiscus is a kind of bush)
'such a reversal a bird in' is the wordplay.
'a reversal' is a reversal indicator.
'a bird' becomes 'ibis' (ibis is a kind of bird).
'in' is an insertion indicator.
'such' back-to-front is 'hcus'.
'hcus' enclosing 'ibis' is 'HIBISCUS'.
'the' acts as a link.
(Other definitions for hibiscus that I've seen before include "His cubs I change for a fragrant flower" , "Genus of mostly tropical plants" , "The rose mallow" , "Malaysian national symbol" , "Largely tropical flower" .)