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.
Maybe you can see an association between them that I don't see?

'from avon's source spreading over banks' is the wordplay.
'from' becomes 'o' (I've seen this in other clues).
'source' indicates taking the first letters (source can mean a beginning or origin).
'spreading' is an insertion indicator (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' placed within 'lenders' is 'leanders'.
'o'+'leanders'='OLEANDERS'

Can you help me to learn more?