Regimen is proven to regenerate flower (7,8)
I believe the answer is:
evening primrose
'flower' is the definition.
(I've seen this before)
'regimen is proven to regenerate' is the wordplay.
'to regenerate' indicates an anagram.
'regimen'+'is'+'proven'='regimenisproven'
'regimenisproven' with letters rearranged gives 'EVENING-PRIMROSE'.
(Other definitions for evening primrose that I've seen before include "Plant with pale yellow flowers" , "Bloomer" , "plant that flowers at night" , "type of oil" , "flower" .)