Plant pruned by total mug (9)
I believe the answer is:
buttercup
'plant' is the definition.
(buttercup is a kind of plant)
'pruned by total mug' is the wordplay.
'pruned' means to remove the last letter.
'total' becomes 'utter' (I've seen this in another clue).
'mug' becomes 'cup'.
'by' with its final letter taken off is 'b'.
'b'+'utter'+'cup'='BUTTERCUP'
(Other definitions for buttercup that I've seen before include "growth in the field" , "Rich yellow wild flower" , "Bumboat woman" , "Bright yellow flower" , "Common grassland plant, poisonous to livestock" .)