Small companies producing lettuce (3)
I believe the answer is:
cos
This clue could be a double definition.
'small companies' is the first definition.
'cos' can be an answer for 'companies' (I've seen this in other clues). I'm not certain of the 'small' bit.
'lettuce' is the second definition.
(cos is a kind of lettuce)
'producing' acts as a link.
Can you help me to learn more?
(Other definitions for cos that I've seen before include "holiday destination" , "Senior officers" , "foreign island" , "Greek island and type of lettuce" , "Mozart fidelity-test opera" .)