"And the tree of the knowledge of good and evil." What was that tree from which the first man ate? Rabbi Meir says: it was wheat. For when a person has no understanding, people say, "That man has not eaten a piece of wheat bread in his days." Is it possible it was wheat, when Scripture writes "tree"? They were tall as the cedar of Lebanon.
Rabbi Meir Says the Tree of Knowledge Was Wheat
Yalkut Shimoni on Torah 21:2
וְעֵץ הַדַּעַת טוֹב וָרָע. מֶה הָיָה אוֹתוֹ הָאִילָן שֶׁאָכַל מִמֶּנּוּ אָדָם הָרִאשׁוֹן. רַבִּי מֵאִיר אוֹמֵר, חִטִּים הָיוּ, כַּד לָא הֲוָה בְּבַר נַשׁ דֵּעָה אִנּוּן אָמְרִין לֹא אָכַל הַהוּא גַּבְרָא פִּתָּא דְּחִטִּין מִן יוֹמֵי אֶפְשָׁר חִטִּין הָיוּ וְהָכְתִיב עֵץ, מִתַּמְּרוֹת הָיוּ כְּאֶרֶז לְבָנוֹן.