Come to think of it, Elven flour may not have been made from any relative of grain as we know it. After all, grains require a considerable amount of cleared land to grow and the Galadrim (lembas bakers extraordinare) didn't seem to have much, if any in Lothlorien. What do you want to bet that lembas flour was made from some kind of nut? Mallorn nuts, maybe? We know from ROTK that the Party Field mallorn was grown from a nut Sam found in the box of earth Galadriel gave him.