Seed a Parisian turned up in vegetable matter (6)
I believe the answer is:
peanut
'seed' is the definition.
(peanut is a kind of seed)
'a parisian turned up in vegetable matter' is the wordplay.
'a parisian' becomes 'un' ('a' in French).
'turned up' shows that the letters should be reversed in order.
'in' means one lot of letters goes inside another.
'vegetable matter' becomes 'peat' (I've seen this in another clue).
'un' reversed gives 'nu'.
'nu' placed into 'peat' is 'PEANUT'.
(Other definitions for peanut that I've seen before include "One of little importance -- ante up (anag)" , "Ante up for the popular snack" , "Ante up for the popular kernel" , "A monkey delicacy" , "sort of butter" .)