Somehow elect trade union leaders of the greens (7)
I believe the answer is:
lettuce
'greens' is the definition.
(lettuce is a kind of greens)
'somehow elect trade union leaders of' is the wordplay.
'somehow' indicates an anagram.
'leaders of' indicates taking the first letters.
The initial letters of 'trade union' is 'tu'.
'elect'+'tu'='electtu'
'electtu' is an anagram of 'LETTUCE'.
'the' acts as a link.
(Other definitions for lettuce that I've seen before include "Leaves for a course" , "Green stuff used in salads" , "Plant with broad crisp leaves used in salads" , "Harvest festival item" , "Cos or iceberg?" .)