Grapefruit half. View of a grapefruit (Citrus paradisi) which has been sliced in two. The grapefruit is a large and bitter-tasting citrus fruit. It is a good source of vitamin C (ascorbic acid) and is a low calorie food. Pink-fleshed varieties have been bred, which retain the same taste, but are less bitter than the natural grapefruits. The grapefruit is thought to have originated in the West Indies as a mutation or natural hybrid of the pomelo (or shaddock, Citrus maxima). It is now grown in tropical climates all over the world, however its main source is Florida, USA.