This plant's turnover makes phenomenal contribution (7)
I believe the answer is:
anemone
'this plant's' is the definition.
(anemone is a kind of plant)
'turnover makes phenomenal contribution' is the wordplay.
'turnover' shows that the letters should be reversed in order (the letters turn over).
'contribution' indicates a hidden word (letters from the answer contribute to the clue).
'enomena' can be found hidden inside 'makes phenomenal'.
'enomena' back-to-front is 'ANEMONE'.
(Other definitions for anemone that I've seen before include "climbing plant" , "Bright flower or sea plant" , "Sea plant or garden flower" , "Buttercup-like flower or sea animal" , "bloomer" .)