Short answers, pulled from the story.
Juglans is derived from two Latin words: jovis, meaning Jupiter, the chief god of ancient Roman religion, and glans, meaning acorn or nut. Regia means regal or royal, referring to the quality of the fruit and edible nuts.
Juglans regia is native to Eurasia, with Iran and Central Asia recognized as centres of origin and diversity. Its exact natural range is difficult to determine because the tree has been cultivated for possibly as long as two thousand years, obscuring its original distribution.
Early American settlers used the name "English walnut" to distinguish Juglans regia from the black walnut and butternut native to North America. Alan Mitchell noted this was an error by early settlers; the botanically accurate name is Persian walnut.
In 2022, world production of shelled walnuts was 3.9 million tonnes. China led with 36% of the total, followed by the United States, Iran, and Turkey as secondary producers.
Benevento in southern Italy is home to an ancient tradition of stregoneria, or witchcraft. Witches from across Italy were said to gather under a sacred walnut tree for the Witches' Sabbath. In 1526, Judge Paolo Grillandi wrote of witches in Benevento who worshipped a goddess at the site of an old walnut tree. The legend inspired the 1812 ballet Il Noce di Benevento and Niccolò Paganini's violin piece Le Streghe.
Fallen walnut leaves and husks contain juglone, a chemical that acts as a natural herbicide. This prevents many other plant species from establishing themselves beneath the tree's canopy.