Barge capsized shown in national emblem (4)
I believe the answer is:
leek
'national emblem' is the definition.
(I've seen this before)
'barge capsized' is the wordplay.
'barge' becomes 'keel' (both are a type of boat).
'capsized' says the letters should be written in reverse.
'keel' backwards is 'LEEK'.
'shown in' is the link.
(Other definitions for leek that I've seen before include "Plant; Welsh emblem" , "Vegetable - Welsh emblem" , "Welsh national emblem" , "Welsh symbolic vegetable" , "Edible plant, Welsh symbol" .)