There are various types of walnut, but the species grown for food (of their seeds) are two: Persian walnut or English walnut, and black walnut . They both belong to the Juglandaceae Family and Genus Juglans ; the first is from the Specie regia, while the second is from the Specie nigra . The binomial nomenclature of these plants is Juglans regia and Juglans nigra .
English walnut (J. regia) was born in Persia, while black walnut (J. nigra) is native to the eastern portion of North America.
The fruit of black walnut has excellent organoleptic and taste characteristics but, due to the hardness of the shell and the difficulty in shelling the seed, it is not marketed in a significant way.
On the other hand, there are many fruits obtained from cultivars developed from English walnut or Persian.
Another lesser known species are the Junglans californica or Californian walnut (used as a grafted port of the Juglans regia), the Juglans cinerea or butternuts (butter nut / oil) and Juglans major or Arizona walnut (the largest walnut tree) . The Juglans microcarpa or Texas walnut produces bunches of very small fruits; the variety J. m. microcarpa finds application in the cross (by pollination) with the Juglans major and with the Juglans nigra, obtaining plants with intermediate characteristics.
