Lemon is a rare breath of fresh air in the citrus family
The author jokes
To finish this article, I drank at least five glasses of iced lemon tea...
Uh, the messy family history of citrus fruits (Citrus spp.) has probably been heard by everyone: people never tire of fretting over this gossip, and even derived a legal-style lily story of sisters attracting each other (not really...). This eventually caught the attention of Nature magazine. Earlier this year, big-name scientists published for the first time a comparison of various citrus fruits at the whole-genome level, concluding that the citrus situation has changed.
Fortunately, I checked again that what we are talking about today is lemon (Citrus x limon), which hascitron(C. medica) as thepaternal parentandbitter orange(C. x aurantium) as thematernal parent. The species epithet of bitter orange also has an x in front of it, indicating that it too originated from hybridization: its father is the pure mandarin (C. reticulata), and its mother is the pomelo (C. maxima). In short, it is still a fairly simple story among three pure lineages. Compared with the chaotic things that happened later to other members of the citrus family, it could almost be called a model family.
Today's protagonist, as pure as a little daisy, the fresh and lovely lemon. Image: Pixabay
Its family history is... not that simple either
The story begins about eight million years ago,in the late Miocene. At that time, on the African continent, the ancestors of humans and chimpanzees had just split; on the North American continent, three-toed horses were still running; and the collision between India and the Eurasian continent had reached its climax, with the Himalayas rising intensely, causing the climate to begin drying and cooling, the oceanic monsoon to weaken, and vast grasslands to appear in the central part of the continent. The ancestor of Citrus, living in the forests at the foot of the Himalayas (probably in the region between today's northern Myanmar, Assam, and western Yunnan), began "adaptive radiation" as the terrain and climate changed, meaning it evolved in various directions into different species.
The dispersal and evolutionary history of Citrus inferred from reconstructing ancestral genotypes. The red five-pointed star represents the Miocene Citrus fossil site in Lincang, Yunnan. Image: Wu et al. 2018 / Nature 554: 311-316; Chinese adaptation: Plover
Today, the Miocene fossil C. linczangensis found in Lincang, Yunnan, may represent what theCitrus ancestorlooked like at that time: it hada typical "unifoliolate compound leaf". Unlike the extant northern species trifoliate orange (C. trifoliata), which has the typical trifoliolate compound leaf of Rutaceae, the lateral leaflets of the Citrus ancestor's compound leaf degenerated and merged with the leaf rachis, making the compound leaf look as if only one small leaflet is attached to a winged petiole (the "single" look...). As for trifoliate orange, it is not produced by "oranges grown north of the Huai River"; it diverged from citrus species much earlier and should even be placed in another genus (Poncirus). In 1984, a more primitive species of the same genus, P. polyandra, was discovered in Fumin, Yunnan.
The left image shows the Miocene Citrus C. linczangensis fossil leaf found in Lincang; even its unifoliolate compound leaf is in the shape of love for you. The right image shows the trifoliolate compound leaf of trifoliate orange. Image: Xie et al. 2013 / Intl. J. Plant Sci. 174(8): 1201-1207; Magyar / Wikimedia Commons
The hybridization and evolutionary relationships of common commercially sold Citrus fruits. Image: Wu et al. 2018 / Nature 554: 311-316; Chinese adaptation: Liu Su
The Citrus species that split apart retained a habit that gives biologists headaches and that working people delight in:they can occasionally hybridize with relatives of the same genus, still like a family that loves one another. Citrus that entered China was called "loose-skin orange" because of the important trait of being easy to peel. Later, food lovers used it and continuously did unspeakable things with pomelo (repeated hybridization and backcrossing of descendants to gradually introgress pomelo genes) toreduce acidity and improve taste, giving rise to today's various mandarins and oranges。
Fortunately, two million years ago, during a certain Pleistocene glacial maximum, citrus that had not encountered humans crossed a land bridge to Japan and was called tachibana (C. r. subsp. tachibana, also called tangerine in Taiwan = =|||), which counts as leaving behind a subspecies as pure as the loose-skin orange. However,the Japanese word "yuzu"is actuallya hybrid of pure mandarin and Ichang papeda, the fragrant orange (C. x junos); of course, that is a later story...
The fragrant orange, also called "yuzu" in neighboring countries (Japanese yuzu or Korean yuja), actually has Ichang papeda genes. Yes, it is what is used in yuzu tea. Image: ???? / Wikimedia Commons
How did lemon come about
Since the Chinese people are so good at cultivating Citrus fruits, why does the name "lemon" sound so much like a transliteration? Judging by limon in the scientific name, was it translated by a southerner who could not distinguish nasal sounds from lateral sounds? Actually, the matter is not that simple.
Probablythe Chinese discovered or cultivated very earlythe hybrid of pure mandarin and pomelobitter orange. As mentioned earlier, this is a simple parental family story, very likely occurring naturally early in species divergence. But its name contains "sour," so Chinese interest turned to cultivating the various sweeter mandarins and oranges that came later, whilebitter orange spread to the West, possibly meeting in India, as if by destiny, the father of all lemons and limes, citron: in Sanskrit lemon is nimbu, which further west became Old Persian and Arabic limun, and then Latin limon (so even if you want to blame someone, blame some ancient Persian or Arab who could not distinguish l from n...)
The Sheikh Lotfollah Mosque from the Persian Safavid period, located in Isfahan, its interior dome painted all over with exquisite lemon-shaped (or perhaps actually eye-shaped) patterns. Lemon lovers must make a pilgrimage (just kidding). Image: Phillip Maiwald / Wikimedia Commons
Citron is said to be self-enclosed and odd because it evolvedcleistogamy, so it remains pure and is very hard to hybridize with other species. It also developed on its own the strange deformed form with separate carpels, "Buddha's hand." But every rule has exceptions. The promiscuous citrus also successfully made citron the father of rough lemon (C. x jambhiri); we believe this was an ancient natural hybridization (perhaps before citron developed its good habit of being self-enclosed). Later, with human help, citron'spollen was used to breed various species that needed its pure fragrance, so it became a father in all sorts of ways...
The paternal parent of all lemon and lime fruits: citron Citrus medica. This is what its fruit looks like when it does not split into "Buddha's hand." Image: Marrabbio2 / Wikimedia Commons
The peoples of South Asia and West Asia pairedroasted meat with the fragrance of citron and the flavor of bitter orange, and it was just right. Thisperhapsprompted the birth of lemon. Although as early as 90 BCE there was the incident of Jews in Jerusalem throwing lemons at priests who had erred, and by no later than the second century CE there are records of lemons reaching Italy under ancient Roman rule, neitherrules out the possibility that they were merely some cultivated variety bred from citron. The Old Persian limun was merely a general term for "citrus fruits." After all, even the first edition of Linnaeus's Species Plantarum still classified lemon under the species citron.
Lemon trees are now also cultivated outside the Catholic church in Bethharan, a city mentioned in the Bible. Image: lpj.org
The lemon as we know it today was probably introduced to Persia, Iraq, and Egypt for cultivation in the 8th century during the rise of Islam, and was first described in Arabic agricultural literature in the 10th century. It was initially an Islamic garden plant and later spread to the Mediterranean region. Large-scale lemon cultivation in Europe began in Genoa in the mid-15th century, and thenlemon seeds were brought by Columbus to the New World. Only today can we eat American lemon tarts or Mexican lemon pie...
As for the limonia (Citrus x limonia) that the great food lover Su Shi might have known, now semi-wild in southern China, it is another hybrid of citron and mandarin,perhaps related to Muslim caravans sailing eastward。
What is called limonia in Chinese today is a hybrid of citron and mandarin; it is unknown whether what Su Shi spoke of back then was also this. Image: Amada44 / Wikimedia Commons
The lemon that can save lives
It is intriguing that Muslim fleets may have known very earlythat lemon could treat scurvy, but even though Vasco da Gama, upon reaching India, was told of this, 116 of his 170 crew members still died from this deadly disease that causes aching limbs, bleeding gums, and weakness. Later, Magellan's circumnavigation fleet was almost completely wiped out, and the cause of death for most crew members was also scurvy. Thinking that Columbus may have brought lemon seeds to the Americas in 1492 is truly lamentable.
But those people and their erarepresented humanity's first explorations in having the courage to challenge ultra-long-distance voyages. On earlier short voyages, it was relatively easy to replenish fresh food along the way, but in the 16th century, when the scientific spirit had not yet been accepted, it was difficult for people to systematically analyze lemon's effect in treating scurvy. Moreover, lemons on ships were not easy to keep fresh. Later, as the two great empires of Spain and Portugal increased the number of strategic ports where they could resupply along the route, lemon's role unexpectedly ceased to be valued...
From the late 15th century to the early 16th century, those great new sea routes that connected the world and their pioneers: Columbus, Vasco da Gama, Magellan. Image: George M. Wrong 1905 / Internet Archive Book Images
In the following centuries, people recognizedthe importance of supplementing fresh vegetables for preventing and treating scurvy. In 1747, British Royal Navy ship surgeon James Lind, for the first time through scientific controlled experiments, confirmed the effect of lemons and oranges in treating scurvy. Unfortunately, the treatment method he recommended was only a small paragraph in a very long report, andvitamin C, only discovered in the 20th century, was not yet known as the fundamental cause of all this, so in the 18th century the number of Royal Navy deaths from scurvy still exceeded combat losses. It was not until the circumnavigation of 1768-1771 that Captain Cook, who had read Lind's report, finally did not let any crew member die of scurvy.
A painting depicting James Lind treating scurvy with lemons. Image: Institute of Naval Medicine / BBC
Among the remedies for treating scurvy, there is also a class of fruit called lime in English, perhaps from Arabic laymun, cognate with the word lemon. Most of them are "lime lineage" fruits that do not contain mandarin or bitter orange genes, a series of masterpieces from father citron and mother small-flowered orange. One of the most common is the round, smooth lime now popular inCorona beer or mojito cocktails, transliterated as "laimeng." The lime (C. x aurantifolia) also has various complex ploidy changes and hybridizations, producing different diploid, triploid, and tetraploid strains.
Mojito, the popular drink made with rum as the base spirit plus lime, mint, and soda water, should actually be transliterated as mohito according to authentic Cuban pronunciation. Image: TheCulinaryGeek / flickr
A bit of extra gossip about the wild maternal parent of lime, the small-flowered orange: its evolution on the Southeast Asian islands is puzzling. It is very likely a synonym of the wrinkled kaffir lime (C. hystrix) commonly used in Thai cuisine, or at least shared an ancestor with kaffir lime during some period. In addition, it also shares an ancestor with three species including the Australian lime (C. australis). These should all be natural origins without human intervention. Ultimately, humans hybridized it with citron to produce various other limes...
Once again I feel fortunate that today's topic is the yellow, pure, and beautiful lemon, rather than the various limes whose pedigrees are just as chaotic as China's citrus fruits (abbreviated as the orange ovals in the figure)... I have no energy to translate it all. Just remember that the wild species in the top row, from left to right, are small-flowered orange, citron, mandarin, and pomelo. For the rest, please look at the Latin scientific names and English names and figure it out yourselves. Image: Curk et al. 2016 / Annals of Botany 117(4): 565-583
Traditionally, biology'sdefinition of speciesisreproductive isolationbetween populations. In the long changes of nature, genes gather into interwoven long rivers flowing onward to descendants, separated by mountains and oceans, or living in the same place yet lacking a pollinator, creating what we recognize as species. Butrandom infiltration and exchange are always unavoidable, and besides, destiny is not entirely governed by one's own genes: pollinators and climate change, and the best part is yet to come. Industrious and brave social species such as humans also use acquired habits, values, and other cultural memes that can be called "memes" to stir the tiny streams of genes, letting species and civilizations evolve in entanglement...
This article is the 277th article of the 4th year of Species Calendar, from Species Calendar author @Plover.