Riverbank plant (5)
I believe the answer is:
sedge
'riverbank plant' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sedge that I've seen before include "water-loving vegetation" , "Plant of wet ground" , "Bog plant; type of warbler" , "fly by rivers" , "Plant growing in swampy ground" .)