There are separate entries for calamansi, citron, grapefruit, lemon, lime, mandarin, mandarin limes, orange, pomelo, ugli, yuzu. Here, these fruits are considered as a family.
All citrus fruits are native to a region stretching from E. Asia southwards to Australia. Collectively they now constitute the third most important group of fruits; only the apples and pears, and the banana and plantain, surpass them in quantity produced and consumed.
Botanists have calculated that the history of the citrus trees goes back 20 million years, to a time when Australia was joined to Asia. Given this span of time, and the ease with which hybridization takes place, it is remarkable that so much of the development of the fruits has taken place in historical times, even in the last few centuries—the grapefruit dates back only to the 18th century.