Plant — wild shrub so containing prickle, ultimately? (8)
I believe the answer is:
rosebush
'plant' is the definition.
'wild shrub so containing prickle ultimately?' is the wordplay.
'wild' indicates an anagram.
'containing' is an insertion indicator.
'ultimately?' indicates one should take the final letters (I've seen 'ultimately' mean this).
The last letter of 'prickle' is 'e'.
'shrub'+'so'='shrubso'
'shrubso' with letters rearranged gives 'rosbush'.
'rosbush' placed around 'e' is 'ROSEBUSH'.
(Other definitions for rosebush that I've seen before include "shrub" , "Flower supplier" , "Plant" , "Thorny growth" .)