Botanist's first walk for pleasure to get prickly plant (7)
I believe the answer is:
bramble
'prickly plant' is the definition.
(I've seen this before)
'botanist's first walk for pleasure' is the wordplay.
'first' indicates taking the first letters.
'walk for pleasure' becomes 'ramble' (I've seen this before).
The first letter of 'botanist' is 'b'.
'b'+'ramble'='BRAMBLE'
'to get' is the link.
(Other definitions for bramble that I've seen before include "Thorny bush" , "Rough, prickly shrub" , "berries" , "Prickly hazard" , "Prickly plant yielding blackberries" .)