Its origins are vague, but the native Jamaican ugli fruit is believed to be a tangerine-grapefruit hybrid (though the pomelo may also have been involved). It ranges in size between that of a navel orange and a giant grapefruit. Its acid-sweet flavor suggests grapefruit with hints of orange. The extremely thick, yellow-green skin fits rather loosely over the large, juicy, yellow-orange pulp sections. Ugli fruit is available on a limited basis around the country from winter to spring. Choose fruit that's heavy for its size and that gives slightly to palm pressure. Store at room temperature and use within 5 days or refrigerate up to 3 weeks. Ugli fruit may be prepared and eaten in any way suitable for grapefruit. It's an excellent source of vitamin C.