Plant duke, rotten, back in parliament (8)
I believe the answer is:
daffodil
'plant' is the definition.
The answer is an example.
'duke rotten back in parliament' is the wordplay.
'duke' becomes 'd' (abbreviation).
'rotten' becomes 'off' (rotten food is 'off').
'back' shows that the letters should be reversed in order.
'in' indicates putting letters inside.
'parliament' becomes 'dail' (I've seen this before).
'd'+'off'='doff'
'doff' in reverse letter order is 'ffod'.
'ffod' put into 'dail' is 'DAFFODIL'.
(Other definitions for daffodil that I've seen before include "Plant of the genus Narcissus" , "Yellow spring flower beloved of Wordsworth" , "National flower of Wales" , "Something yellow for spring" , "Popular yellow flower of spring - ask Wordsworth" .)