The Gemorah cites as an example of Terumah mdrbannon otitz sheno nokuv, why didn'i it give a simpler more common answer of produce thats not subject to terumos and maaser, min hatorah?
Ari
Ari, I found, bs'd, that the Ritva asks a similar question to yours on a Gemara in Gitin 65a. The Gemara there states that a certain Mishnah is referring to a sort of Maaser which is only deRabanan, and to give an example of this the Gemara says it is an otzitz she'eino nokuv which is derabanan.
The Ritva asks why does the Gemara not answer that we are referring to Maaser Sheni which is only liable miderabanan, for instance fruit that grows on trees, or vegetables?
The Ritva answers that this sort of Maaser possesses an "Ikar Min Hatorah" (it has "a root in the Torah"), whilst otzitz she-eino nokuv does not have ikar min hatorah.
It seems that what the Ritva means is that if, for instance, wheat would grow on the same field it would be liable for Maaseros Mideoraisa. Therefore fruit of the trees or vegetables are closer to being liable mideoraisa. In contrast any kind of produce which grows in an otzitz she-eino nokuv can always only be maaser miderabanan. Therefore when the Gemara looks for an example of masser which is only miderabanan, it chooses otzitz she-eino nokuv which can never come to being liable according to the Torah.
[see also Sha'ar Hamelech Hilchos Maaser Sheni 1:12]
KOL TUV
Dovid Bloom