What are the Five Pungent (Vegetables/Roots/Spices) and when were they first proscribed? According to Salguero (2017):


  The Five Pungent Roots generally refer to garlic, leeks, scallions, onions, and asafoetida, as well as their subvarieties. In some sources, the list includes ginger and chives.


I am looking for a more definitive reference for this. In particular, I am looking for any early Buddhist texts that proscribe the "Five Pungents" and, better still, explicitly names the five.
At the risk of posting something that's more of a comment rather than an answer ...

I thought of "Jains" (from the same kind of era as Buddhists) -- apparently they too don't eat garlic, leeks, scallions, onions (apparently their rationale is that these are root vegetables) -- but (I may be wrong) I read that they (and Brahmins) can eat asafoetida. I don't know the history of it though, nor the Buddhism.

I suppose you might look in the Vinaya (where else?), for what you're looking for.

Can monks and nuns eat garlic? (for example) gives a reference to this, which includes ...


  Monks, garlic should not be eaten. Whoever should eat it, there is an offence of wrong-doing.


... and ...


  I allow you, monks, to eat garlic in the case of illness.


And the last post in that thread says ...


  Should the same approach of moderation be taken for all five "pungent spices," i.e., leeks, scallions, garlic, onion, and ginger (if I have them correctly)?


... which might make sense? Ginger is "pungent" and is another plant-root (avoiding plant-roots is, I think, part of being as harmless as possible -- in the Jain doctrine at least -- I think that forest-dwelling Buddhist monks, too, aren't supposed to dig i.e. disturb the soil).