> Buckwheat

That one's not common in food in the US, either. A lot more "odd" ingredients are widely available now than used to be in the US, so you can find it without too much trouble, but it's still not something most are familiar with. I cook a fair bit and I've only used it because I decided to try making Breton buckwheat crêpes, and I'm sure I could find other ways to use it but I'd have to go out of my way to do so. Wouldn't be surprised if it's present in a couple regional US cuisines in a minor way (cajun?) but it's not something most people eat regularly, if at all.