White? Rose provided if not (9)
I believe the answer is:
otherwise
'if not' is the definition.
(synonyms)
'white? rose provided' is the wordplay.
'provided' indicates an anagram (I've seen 'provide' mean this).
'white'+'rose'='whiterose'
'whiterose' anagrammed gives 'OTHERWISE'.
(Other definitions for otherwise that I've seen before include "Under different conditions" , "White rose (anag.)" , "White rose seen in a different way" , "Differently - or else!" , "in different circumstances" .)