Peanuts are the most consumed nuts in the US but aren't really nuts - they're peas. True nuts grow on trees. Brazil nuts, pecans, chestnuts, almonds etc.
Cashews are native to South America but are now grown prmarily in India and are "kin" to mango. The cashew comes from a tree with an odd little fruit called the cashew apple. Hanging off the end of each of these fruits is a shell containing one cashew. On a side note the shell has an oil often used in furniture varnishes becasue it repels termites. So one cashew apple one cashew and getting these to market isn't easy, so cashews are expensive.
Pistachios are grown from the Middle East all athe way int oAsia. The pistachio tree was inroduced inot California in the 1890s. The trees seed twice per year, prodicing clusters of seeds incased ina fleshy yellow-red skin.These seeds are harvested by tree shaking machines and then the clusters are picked off the grounm soaked in water (to remove fleshy coating) and dried in the sun. The nut is a deep green, the deeper the green the better and more highly valued the nut. The green is due to th epresence of chlorophyll. The red color some shells have is just a red dye. Pistachios split or "smile" when ripe and thus are easy to remove from their shells.
Macadamia nuts are indigenous to Australia but centurie of transplanting has brought them to their adopted home of Hawaii. It takes a tree seven years to produce a marketable crop so they are expensive. They have a high fat content and a flavor slightly tropical and when toasted taste a little like coconut.