What is “nuez de Brasil” vs “castaña” in Spanish?

Nueces de Brasil are Brazil nuts, the big selenium-rich seeds. The catch is that nuez is the umbrella word for “nut” (and specifically the walnut), so the name marks them as the Brazilian nut. Cross into South America, though, and the very same food is usually a castaña — castaña de Pará or castaña amazónica — even though castaña normally means chestnut. One nut, two completely different family trees of names.

This is a classic regional-vocabulary trap: a Spaniard hears castaña and pictures a roasted chestnut, while a Bolivian or Peruvian means the Amazon nut you are eating for its selenium. Spanish nut words are slippery in general — cacahuate versus maní for peanut is the same story. When a recipe or health video says castaña, check the country before you guess which nut is on the table.