What might be a warning device for the plant (8)
I believe the answer is:
hawthorn
'the plant' is the definition.
The answer is an example.
'what might be a warning device' is the wordplay.
'might be' indicates anagramming the letters.
'a warning device' becomes 'horn' (horn is a kind of warning device).
'what' anagrammed gives 'hawt'.
'hawt'+'horn'='HAWTHORN'
'for' acts as a link.
(Other definitions for hawthorn that I've seen before include "Spiky tree with small red berries" , "plant" , "Spring-flowering shrub" , "Spring-flowering small tree with small dark red fruit" , "Hedge-tree" .)