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 found within the answer.
The remaining letters 'gi' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'serving' is the 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?" .)