Bird nesting in the said overturned bush (8)
I believe the answer is:
hibiscus
'bush' is the definition.
(hibiscus is a kind of bush)
'bird nesting in the said overturned' is the wordplay.
'bird' becomes 'ibis' (ibis is a kind of bird).
'nesting in' indicates putting letters inside.
'the said' becomes 'such' (both can mean 'the previously mentioned').
'overturned' is a reversal indicator.
'such' written backwards gives 'hcus'.
'ibis' going into 'hcus' is 'HIBISCUS'.
(Other definitions for hibiscus that I've seen before include "Malaysian national symbol" , "Large-flowered plant of the mallow family" , "Genus of mostly tropical plants" , "Largely tropical flower" , "brightly coloured flowers" .)