Decay found in vegetable plant (6)
I believe the answer is:
protea
'plant' is the definition.
The answer is an example.
'decay found in vegetable' is the wordplay.
'decay' becomes 'rot' (rot is a kind of decay).
'found in' is an insertion indicator.
'vegetable' becomes 'pea' (pea is a kind of vegetable).
'rot' placed within 'pea' is 'PROTEA'.
(Other definitions for protea that I've seen before include "South African plant" , "South African evergreen" , "South African shrub" , "Ascend" , "S. African shrub; to pear (anag.)" .)