The two most common major species of walnuts are grown for their seeds – the Persian or English walnut and the black walnut. The English walnut (J. nigra) is native to eastern North America. The black walnut is of high flavor, but due to its hard shell and poor hulling characteristics it is not grown commercially for nut production. Numerous walnut cultivars have been developed commercially, which are nearly all hybrids of the English walnut.
Other species include J. californica, the California black walnut (often used as a root stock for commercial breeding of J. cinerea (butternuts), and
In 2014, worldwide production of walnuts (in shell) was 3.46 million tonnes, with China contributing 46% of the world total (table).Other major producers were (in the order of decreasing harvest): United States, Iran, Turkey and Mexico.