Grassy plant (5)
I believe the answer is:
sedge
'grassy plant' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sedge that I've seen before include "Wetland grass-like plant" , "Marsh grass" , "Grass-like plant growing in marshes" , "Marsh-dweller" , "Bog plant; type of warbler" .)