Flowering plant in old dean’s novel (9)
I believe the answer is:
dandelion
'flowering plant' is the definition.
'in old dean's novel' is the wordplay.
'novel' indicates an anagram.
'in'+'old'+'dean'='inolddean'
'inolddean' with letters rearranged gives 'DANDELION'.
(Other definitions for dandelion that I've seen before include "Common yellow-flowered weed" , "Wild plant with "clock"" , "Wild flower with serrated leaves" , "One blooming" , "Weed with deeply incised leaves" .)