Thames-side trees whence many flowers have come (4,4)
I believe the answer is:
nine elms
'thames-side' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'trees whence many flowers have come' is the wordplay.
I cannot really see how this works, but
'trees' could be 'elms' (elm is a kind of tree) and 'elms' is found in the answer.
'many' could be 'nine' (example) and 'nine' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for nine elms that I've seen is " part of Wandsworth - with 25d".)