Sample overturned mushrooms by abandoned mine (8)
I believe the answer is:
specimen
'sample' is the definition.
(specimen is a kind of sample)
'overturned mushrooms by abandoned mine' is the wordplay.
'overturned' shows that the letters should be reversed in order.
'mushrooms' becomes 'ceps' (I've seen this before).
'by' says to put letters next to each other.
'abandoned' is an anagram indicator.
'ceps' back-to-front is 'spec'.
'mine' is an anagram of 'imen'.
'spec'+'imen'='SPECIMEN'
(Other definitions for specimen that I've seen before include "Something serving as an example" , "Example regarded as typical of its class" , "Example of type" , "Part taken as example of whole or class" , "Representative sample" .)