Oranges and lemons are generally thought to be the most prototypical citrus fruits, being the most commercially successful. But originally there were only four types of citrus fruits, and both the orange and lemon are hybrids of those original four. Citruses originally come from south-east Asia, and the first mention of them is in Chinese literature from 2200 BC. They've been domesticated since around 500 BC, and spread to the occident only very slowly, with the lemon being first grown in Spain in 1150 AD.
Since domestication happened so early, it's difficult to reconstruct which species are original, and which are hybrids, but the four oldest of the citruses appear to be as follows:
- Citrus aurantifolia (Lime)
- Citrus maxima (Pummelo)
- Citrus medica (Citron)
- Citrus reticulata (Mandarin)
The lime was introduced to Europe during the crusades. The pummelo, or pamplemousse as it is in French, was introduced at about the same time, and had already been commercially grown in China for many centuries. The citron, however, was the first of the citruses to be known in Europe, mentioned by Pliny in his Natural History. Having been introduced to Europe by Alexander the Great's armies, it was used first as a perfume and then as a food. The mandarin was the last to be introduced to Europe, in the 19th century, despite having been commercially grown in China at the same time as the pummelo. The satsuma and the tangerine are both varieties of the mandarin.
The three most common hybrids, some of which were introduced to Europe before the original citruses, were bred as follows:
- Lemon, Citrus limon (citron × lime)
- Grapefruit, Citrus paradisii (pummelo × orange)
- Orange, Citrus sinensis (pummelo × mandarin)
Since all the varieties of citrus hybrid so readily, the practice of doing so is still quite common, and new varieties are being constantly devised. The practice is so common, indeed, it's not actually known how many species of citrus there now are. There are two schools of thought of the subject: the lumpers, after Walter T. Swingle; and the splitters, after Tyozaburo Tanaka. They ascribe 16 and 145 species respectively, but it's generally accepted that the truth lies somewhere in between.
To avoid confusion in naming the hybrids, affixes such as or- or -ange for orange hybrids and lem- or -on for lemon hybrids are employed, but once the hybrids themselves are hybridised, the nomenclature starts to get contrived. It appears that the citruses are becoming a spectrum rather than an easily taxonomisable hierarchy. In any case, some of the new species would probably be very popular if more well known. Who, for example, could resist the lemonage (lemon × orange), or the lemonime (lemon × lime)? I wonder if lemonage juice tastes the same as lemon juice mixed with orange juice?
Still, the orange, known to the taxonomists as the sweet orange, is by far the most popularly produced citrus fruit, at 61.1 megatonnes in 2001, followed by tangerines (16.6 megatonnes) and lemons (10.9 megatonnes), with grapefruits and limes etc. far behind. Tastiness is rather a strange new form of natural selection, though seed propogation via droppings has certainly been around for a while.
Cite: Palmer, S.B. (2005). "Citruses", in: What Planet is This?
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