The floral contribution of autumn from boy (5)
I believe the answer is:
sepal
'the floral contribution' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'autumn from boy' is the wordplay.
'autumn' becomes 'sep' (I can't explain this - if you can you should give a lot more credence to this answer).
'from' is a charade indicator (letters next to each other).
'boy' becomes 'al'.
'sep'+'al'='SEPAL'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for sepal that I've seen before include "Part of a flowering plant" , "Calyx segment" , "Part of a flower - peals (anag)" , "Part of a flower casing" , "Part of a flower's outer envelope" .)