Salad greenery (5)
I believe the answer is:
'salad greenery' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cress that I've seen before include "Salad plant paired with mustard" , "Salad vegetable" , "Plant with pungent leaves used in salads" , "Salad sprouts" , "Cruciferous salad plant" .)