The apple is a pomaceous fruit, prized for its high yields and long storage life. It is easy to ship, resistant to disease, and popular for its flavor which can be sweet or tart, depending on the varietal. Roughly 55 million tons of apples are produced each year. And is a fruit of the genus Malus (about 25 species) belonging to the family Rosaceae, the most widely cultivated tree fruit. The apple is one of the pome (fleshy) fruits, in which the ripened ovary and surrounding tissue both become fleshy and edible. The apple flower of most varieties requires cross-pollination for fertilization. Apples at harvest, though varying widely in size, shape, colour, and acidity, depending upon cultures (variety) and environmental character, are, nevertheless, usually roundish, 50–100 mm (2–4 inches) in diameter, and some shade of red or yellow in colour.