I still think micrantha is just a form of hystrix but didn't know it is a progenitor of modern limes. I also expected maxima to feature more prominently and medica to feature less.
I like the way you think, but I don't think that's true here. I seem to remember reading that kaffir lime was a hybrid of some other type of papeda (I can't remember what it is right now) from which it derived its cold-hardiness. (It was some weird one, not as cold-hardy as Ichang papeda, but maybe I'm not remembering any of this right)
I think kaffir limes are descended from a different papeda ancestor than common limes. Isn't kaffir lime about as cold-hardy as the more cold-hardy oranges? While common limes are the most sensitive out of all the different citrus groups to cold, slightly more sensitive than common lemons.
Edit: I think it may have been
C. latipes, also known as Khasi papeda.
But yes, it's well known that limes are descended from C. micrantha. Another little uncommon fact, C. micrantha is incredibly high in furanocoumarin levels, over four times higher than bergamot! Probably not a good idea to put the essential oil on your skin.
So lemon's primary ancestor is citron, for lime it is C. micrantha, and for kaffir lime it is Khasi papeda (assuming I'm remembering right)
I do suspect citron, C, micrantha, khasi papeda (and Ichang papeda too) are closer related to each other than they are to C. reticula or C. maxima, but that's just judging by morphological appearances.