Matted weeds used as a vegetable (5)
I believe the answer is:
swede
'vegetable' is the definition.
(swede is a kind of vegetable)
'matted weeds used as a' is the wordplay.
'weeds' can be anagrammed to 'SWEDE'.
Though, I am not clear how this is indicated.
Can you help me to learn more?
(Other definitions for swede that I've seen before include "North European" , "Citizen of kingdom" , "A turnip, or a Scandinavian" , "Northern European" , "Root vegetable - European" .)