Every sweet orange descends from a single ancient cross of pomelo and mandarin
The sweet orange is not a wild fruit. It arose in domestication in East Asia from one cross between a pomelo hybrid and a mandarin, and every variety since, from navels to blood oranges, differs only by mutations growers chose to keep. Genetically it is roughly 42 percent pomelo and 58 percent mandarin.
Botanists call it Citrus × sinensis, a member of the rue family, to separate it from the bitter orange, a separate and possibly wild cross between pure mandarin and pomelo parents. The sweet orange's chloroplast DNA, inherited through the mother, is pomelo, so a hybrid pomelo, possibly a backcross, was probably the maternal parent. Its homeland spans southern China, north-east India and Myanmar, and Chinese literature first mentions it in 314 BC. Its full genome has been sequenced.
The orange has gone on to parent other fruits. A backcross with pomelo produced the grapefruit, crosses with mandarins or tangerines gave the clementine and murcott, and pairing with the trifoliate orange created the citranges. Because nearly all citrus species can interbreed, and growers have also propagated spontaneous bud mutations, citrus classification is notoriously messy. Sweet oranges fall into four classes: common, blood, navel and acidless.
The tree is a smallish evergreen, usually 9 to 10 metres tall, though very old specimens reach 15. Botanically the fruit is a hesperidium, a modified berry with a rugged rind grown from the ovary wall, a bitter white pith, and about ten segments of juice-filled sacs. Oranges do not ripen once picked, and in warm climates a fully ripe fruit may stay partly or wholly green.
Production is enormous: 67 million tonnes in 2024, with Brazil growing 23 percent and China and Mexico next. Oranges are eaten fresh or pressed for juice, and the fragrant peel is used too. They have long carried cultural weight. Chinese artists painted them centuries before Jan van Eyck placed one in the Arnolfini Portrait, their first appearance in Western art. By the 17th century a private orangery, like the one at Versailles, was a European status symbol, and later painters from Van Gogh to Matisse returned to them.
Source: Orange (fruit)
