Plant in raid is past reforming (10)
I believe the answer is:
aspidistra
'plant' is the definition.
(aspidistra is a kind of plant)
'raid is past reforming' is the wordplay.
'reforming' indicates anagramming the letters.
'raid'+'is'+'past'='raidispast'
'raidispast' is an anagram of 'ASPIDISTRA'.
'in' acts as a link.
(Other definitions for aspidistra that I've seen before include "Houseplant of lily family" , "The biggest - (in the world) (Gracie Fields)" , "something normally developed in-house?" , "For Asian native" , "Iris adapts (anag) - indoor plant" .)