Old salad ingredient found in Selkirk, perhaps last in Borders (10)
I believe the answer is:
alexanders
'last in borders' is the definition.
Although both the answer and definition are plural nouns, I don't see how they can define each other.
'old salad ingredient found in selkirk' is the wordplay.
I cannot really see how this works, but
'old' could be 'ex' (prefix meaning former or onetime) and 'ex' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for alexanders that I've seen before include "associated with ragtime band?" , "King's" , "salad used to include this" , "Plant" .)