Fenland river god duly uncovered a flower (9)
I believe the answer is:
campanula
'flower' is the definition.
'fenland river god duly uncovered a' is the wordplay.
'fenland river' becomes 'cam' (River Cam).
'god' becomes 'pan' (Pan is an example**).
'uncovered' says to take the centre.
The centre of 'duly' is 'ul'.
'cam'+'pan'+'ul'+'a'='CAMPANULA'
(Other definitions for campanula that I've seen before include "Bell flower" , "Bell-shaped flower" , "Plant" .)