charliehall, good question
i have no idea why corn should be kitnios based on that one very short excerpt from Rav Feinstein, tz’l, but of course it is, that’s the Halachah.
when was the takanh of kitnios begun?
this is from wikipedia:
After European contact with the Americas in the late 15th and early 16th centuries, explorers and traders carried maize back to Europe and introduced it to other countries through trade. Its use spread to the rest of the world.