It’s early December, and somewhere on a mountain on the Japanese island of Shikoku, there’s a citrus tree laden with golden-yellow fruit, each one no larger than a kumquat. There aren’t many of them in the wild. This one might have grown from a large seed, dropped by a bird feasting on the fruit of its cousin from elsewhere. These rare trees cannot survive unless their surroundings are just right, with plenty of sun, space, well-drained soil, and warm temperatures. Scratch the peel of one of those tiny fruits, and…
