Prickly plant in bog, or sedge (5)
I believe the answer is:
gorse
'prickly plant' is the definition.
(I've seen this before)
'in bog or sedge' is the wordplay.
'in' indicates the answer is hidden within the clue.
'GORSE' is hidden within 'bog or sedge'.
(Other definitions for gorse that I've seen before include "Spiny yellow-flowered shrub" , "Wild evergreen shrub with golden-yellow flowers" , "I'm always blooming" , "Spiny evergreen shrub" , "Spiny heathland shrub" .)