Flower grew under weir pump (6,4)
I believe the answer is:
damask rose
'flower' is the definition.
(I've seen this before)
'grew under weir pump' is the wordplay.
'grew' becomes 'rose' (rise can mean to grow or increase).
'under' is a charade indicator (letters next to each other) (below, in a down clue).
'weir' becomes 'dam' (I've seen this before).
'pump' becomes 'ask' (I've seen this in another clue).
'dam'+'ask'='damask'
'rose' put after 'damask' is 'DAMASK ROSE'.
(Other definitions for damask rose that I've seen before include "bloomer" , "source of attar" , "hardy flower" , "Sweet-scented flower yielding attar" .)