Flower and rotten nut they leave on stage (6)
I believe the answer is:
exeunt
'they leave on stage' is the definition.
(stage direction saying multiple actors exit)
'flower and rotten nut' is the wordplay.
'flower' becomes 'exe' (River Exe).
'and' means one lot of letters go next to another.
'rotten' is an anagram indicator.
'nut' anagrammed gives 'unt'.
'exe'+'unt'='EXEUNT'
(Other definitions for exeunt that I've seen before include "More than one exit?" , "Stage direction to a group of actors (Latin)" , "(Actors) depart" , "Stage direction (Latin, they go out)" , "Trivial details" .)