Where did the notion that Adam and Eve ate an APPLE come from? Contrary to popular belief no mention of the fruit being an apple can be found in the Book of Genesis. 

Jewish commentaries recorded in the Midrash Rabbah speculate that the tree might have been a species of wheat, or corn, or that the fruit might have been grapes or figs.

And yet, the idea that it was an apple is widely accepted.

Was it due to Classical influences (The golden apples in the Garden of the Hesperides)? 
Is it a legacy from the Latin 'malum' (apple/evil)? 
Or is there another reason?

Are there any other theories that have been put forward as to what the fruit might have been?
According to the Online Etymology Dictionary, the word apple has, until recently, always meant simply "fruit" in English. This was certainly the case at the time of the earliest English Bible translations in the 1600s.


  In Middle English and as late as 17c., it was a generic term for all fruit other than berries but including nuts (e.g. Old English fingeræppla "dates," literally "finger-apples;" Middle English appel of paradis "banana," c.1400). Hence its grafting onto the unnamed "fruit of the forbidden tree" in Genesis.


(emphasis added)