The origin of the grapefruit poses a bit of a botanical mystery. Its appearance and flavor indicate that it's a hybrid between a large, sour citrus fruit called the shaddock (Citrus maxima) and the sweet orange (Citrus sinensis). No records of any deliberate hybridization between the two plants have been found. Grapefruits share characteristics of both fruits: in a ripe grapefruit the tart flesh of the shaddock is tempered with the juicy sweetness of the orange. Surveys of citrus populations in the Old World and Asia haven't been able to confirm the presence of any native-growing grapefruit trees. Similar searches in the West Indies, however, have uncovered many populations of apparently naturally growing grapefruit. It's a puzzling question whether the grapefruit was deliberately bred or emerged as a spontaneous hybrid in some old Caribbean citrus grove.