More than 30 commercially produced walnuts exist, and they are the oldest-known tree food. The nuts date back to 10,000 B.C. Walnuts are considered to have the medicinal properties of curing bad breath, reducing inflammation and healing wounds.
Walnuts have come to also be known for their nutritional benefits, especially their omega-3 fatty acid content. They also have antioxidants including quinone juglone, tanning tellimagrandin and flavonol morin. A common use of walnuts is in salads.
English walnuts originated in Central Asia, and in the 1700s, they were introduced to California. As of 2015, three-fourths of the world trade and 99 percent of the commercial U.S. supply of walnuts come from California. They are harvested between September and November.
The original Greek word for walnuts is "karyon," which means "head," and it was used because the shell looks like a human skull and the kernel looks similar to a brain.