Amusing American chap, we hear, serving mushrooms (5)
I believe the answer is:
fungi
'mushrooms' is the definition.
(I've seen this before)
'amusing american chap we hear' is the wordplay.
I cannot quite understand how this works, but
'amusing' could be 'fun' (synonyms) and 'fun' is located in the answer.
The remaining letters 'gi' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'serving' acts as a link.
Can you help me to learn more?
(Other definitions for fungi that I've seen before include "Plants like mushrooms and toadstools" , "woodland feature" , "Group with some killers" , "Maybe moulds" , "rusts?" .)