From: Rabbi Moshe Sofer
To: Rabbi Yaakov Baruch Frenkel
A scholar proposes making Pesach matzos from Turkish wheat (buckwheat). The Chasam Sofer conclusively demonstrates it is not wheat but accepts the received tradition classifying it as kitniyos, and permits the poor to make thick matzos from its flour with all stringencies of matzah baking.
Source: Shu"t Chasam Sofer OC §121