Spiny heathland shrub (5)
I believe the answer is:
gorse
'spiny heathland shrub' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gorse that I've seen before include "Ogres (anag.)" , "Wild shrub with yellow flowers and sharp thorns, common on hillsides" , "Prickly heath shrub" , "Spiny yellow-flowered shrub" , "Yellow-flowering shrub" .)