grapefruit, pomelo [key], citrus fruit (Citrus paradisi) of the family Rutaceae (orange family). The grapefruit is so named because it grows in grapelike bunches. The large globular fruit weighs from 1 to 5 lb (0.45–2.27 kg). It is believed that the progenitor of the grapefruit was the pomelo (C. maxima), native to and long a popular fruit in India and other parts of Asia. The pomelo (also called shaddock, for the man who first took it to England as a curiosity) was introduced into the West Indies, where it is thought that a seedling sport or mutation resulted in the grapefruit. Brought to Florida in 1809, the grapefruit had become an important commercial product of that state by the turn of the century. It is now grown in many varieties—chiefly in Florida, Texas, and California in the United States and also in some Mediterranean countries. The tree, an attractive evergreen, is usually propagated by budding. Like other citruses, it is prey to frost and hybridizes easily; the tangelo is a cross between the grapefruit and the tangerine. Furanocoumarins, chemicals found in grapefruit and grapefruit juice, inhibit the enzyme CYP3A4, which reduces the absorption of some drugs in the gastrointestinal tract; eating grapefruit or drinking grapefruit juice while taking those drugs can greatly increase their absorption, causing serious side-effects. Grapefruits are classified in the division Magnoliophyta, class Magnoliopsida, order Sapindales, family Rutaceae.
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