Shrubs from Avon's source spreading over banks (9)

'shrubs' is the definition.
The answer and definition can be both plants as well as being plural nouns.
Perhaps there's a link between them I don't understand?

'from avon's source spreading over banks' is the wordplay.
'from' becomes 'o' (I've seen this in other clues).
'source' suggests taking the first letters (source can mean a beginning or origin).
'spreading' means one lot of letters goes inside another (inserted letters spread others open).
'over banks' becomes 'lenders' (I am not sure about the 'over' bit.).
The first letter of 'avons' is 'a'.
'a' inserted inside 'lenders' is 'leanders'.
'o'+'leanders'='OLEANDERS'

Can you help me to learn more?