Argue over a national fruit (5)
I believe the answer is:
rowan
'fruit' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'argue over a national' is the wordplay.
'argue' becomes 'row' (to row with someone is to argue with them).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'national' becomes 'n' (abbreviation listed in Chambers).
'row'+'a'+'n'='ROWAN'
Can you help me to learn more?
(Other definitions for rowan that I've seen before include "Mountain-ash" , "The mountain ash tree" , "Tree with orange-red berry-like fruits" , "source of berries" , "Canterbury" .)