The family tree of some of the world's most popular fruit has been deciphered.

Citrus fruits have a documented history of cultivation stretching back 4000 years, but until now, no one knew exactly how the fruits were related. A group of researchers from the Southwest University in China used genetic analysis to trace the pedigrees of the sweet, sour and bitter fruits of the Citrus genus.

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The researchers, led by Zhiqin Zhou, found that both sweet and sour oranges are hybrids of mandarin and pummelo. Grapefruit are hybrids of pummelo and sweet orange. Lemons came from citron and sour oranges.

For some fruits, the researchers were even able to determine paternity. Bergamot orange — a bitter fruit most common in Calabria, Italy — derived from sour orange mothers and citron fathers. Limes appeared to be a hybrid of a species of Papeda, an Asian citrus fruit, on the maternal side and citron on the paternal.

 Understanding relationships between citrus trees helps farmers and researchers breed better varieties and avoid disease.

PHOTO 1: Mandarin oranges; Wikimedia Commons

PHOTO 2: Pomelo; Wikimedia commons

PHOTO 3: Bergamot; Wikimedia Commons