Flower against Vauxhall bridges (9)
I believe the answer is:
astrantia
'flower' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'against vauxhall bridges' is the wordplay.
I cannot really understand how this works, but
'against' could be 'anti' (prefix meaning against) and 'anti' is found in the answer.
The remaining letters 'astra' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for astrantia that I've seen is " Plant of the parsley family".)