Teacher returns clutching heads of lettuce and edible nettles (5)
I believe the answer is:
riles
'edible nettles' is the definition.
'riles' can be an answer for 'nettles' (I've seen this in another clue). I am unsure of the 'edible' bit.
'teacher returns clutching heads of lettuce' is the wordplay.
'teacher' becomes 'sir' (way of addressing a male teacher).
'returns' shows that the letters should be reversed in order.
'clutching' means one lot of letters goes inside another.
'heads of lettuce' becomes 'le' (I can't justify this - if you can you should give a lot more credence to this answer).
'sir' reversed gives 'ris'.
'ris' enclosing 'le' is 'RILES'.
'and' is the link.
Can you help me to learn more?
(Other definitions for riles that I've seen before include "Annoys in American way" , "Irritates, nettles" .)