I was reading a Qing story where buckwheat came up, so I had to look it up.

Common buckwheat (Fagopyrum esculentum) is thought to have originated in central and western China from a wild Asian species Fagropyrum cymosum. It has been cultivated in China for over 1,000 years, and was brought to Europe during the Middle Ages.

Doug Eborn says,

It is believed that buckwheat was first domesticated in China.... Whole grain buckwheat is an amazingly nutritious food. Even though it's protein is relatively low at approximately 11%, the protein buckwheat does have contains the eight essential amino acids and is one of the few "grains" (remember that buckwheat isn't a grain at all) high in lysine. If you use half buckwheat flour with your wheat flour, the buckwheat's amino acids will round out the limiting amino acids in your wheat nicely, giving you a nearly perfect balance of the 8 essential amino acids. This particular balance between half wheat and half buckwheat flour is much more closely aligned to your dietary needs even than lean beef!!! It's also rich in many of the B vitamins as well as the minerals; phosphorus, magnesium, iron, zinc, copper and manganese. In addition to this, it's a good oil source of Linoleic acid, one of the two essential fatty acids we must have to be healthy. Nutritionally speaking, buckwheat is a truly impressive food.

Not to mention according to other internet sources, it can ward of cancer and help lose weight. Not that I believe all that.