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Hong Kong is a city of contrasts: of new technology and old traditions, of high-rise buildings and stunning countryside, a hybrid between the East and the West. The territory's flag bears a flower whose past, and future, are just as complicated.
The flag of Hong Kong features a distinctive five-petalled white flower on a red background. This flower became Hong Kong's emblem when the territory washanded over to China in 1997.
But the true origin of this mysterious plant has only been revealed in recent years. It is now the subject of community conservation projects hoping to save it from extinction.
The Hong Kong orchid tree: Bauhinia blakeana Photo: Gurcharan Singh/Alamy
The flower in question is a peculiar plant known as theHong Kong orchid tree. It is a native of the island of Hong Kong.
It is believed that all the Hong Kong orchid trees alive today are descendants of this single plant
Despite its name it is not an orchid, but rather a tree in the legume family, the group that includes peas and beans. However, its distinctive 15cm flowers are reminiscent of orchid flowers, and the common name stuck.
The first Hong Kong orchid tree was found around 1880 byJean-Marie Delavay, a French Catholic missionary out hiking in the countryside. Near a ruined building, he found a single tree with incredible magenta flowers, and took a cutting.
"He thought it was quite stunning, quite beautiful, and quite different to ones he had seen before, and so he took a cutting of it and brought it back to his sanatorium," says data scientistRob Davidsonof the journalGigascience. Sanatoriums were popular in colonial times as a place of respite and recovery for missionaries that had contracted tropical diseases on their travels.
It is believed that all the Hong Kong orchid trees alive today are descendants of this single plant.
Bauhinia blakeana in Hong Kong Photo: EPA European Pressphoto Agency B.V./Alamy
"All the trees since then have been cultivated by hand, by someone who's taken a bit of an old tree, and stuck it on to another root stock and let it grow from there," says Davidson.
The flag of Hong Kong features a distinctive five-petalled white flower on a red background
This process is called "grafting". It has been familiar to gardeners and farmers for thousands of years, so much so that it is easy to forget that it is remarkable.
It is as if someone you could cut the buttocks off one person and stick them onto one leg from another person – and the buttocks then grew a torso, arms and head, and another leg, effectively becoming a copy of the first person, but still with the leg from the other person.
"You can grow tomatoes above ground on the root stock of potatoes that grow underground," says Davidson. The existence ofgraftingis a reminder of how different plants are from animals.
Bauhinia blakeana is iconic Photo: EPA European Pressphoto Agency B.V./Alamy
Some years after Delavay's discovery, a cutting was passed to what is now theHong Kong Zoological and Botanical Gardens. There it was namedBauhinia blakeana. The name honours the 17th-Century botanists Gaspard and Jean Bauhin, and the recently-departed British governor of Hong Kong Sir Henry Blake.
There's 25,000 of them in Hong Kong, and tens of thousands more around the world
The first scientific description of the plant was published by the British botanist Stephen Troyte Dunn in 1908.The description is online as a PDF, beginning on page 351.
Dunn noted both its unusual beauty and its inability to produce seeds. "The tree is at present a very rare one in cultivation and is likely for some time to remain so, as it can only be cultivated by cuttings," he wrote.
But Dunn was dead wrong. TodayB. blakeanais anything but rare.
Bauhinia variegata Photo: Stephanie Jackson - Gardens and flowers collection/Alamy
Since the plant was discovered over 25,000 cuttings have been made. The tree is found throughout Hong Kong, as well as in China, the USA, Australia and elsewhere. "There's 25,000 of them in Hong Kong, and tens of thousands more around the world," says Davidson.
Even when a hybrid does develop into an adult, they are often sterile
Only with modern genetics have scientists begun to unravel the mysterious origins of the Hong Kong orchid tree. A study published in 2005 revealed that the strange flower is actuallya hybrid of two known species; the pink-flowered butterfly tree (B. variegata),and the purple-floweredB. purpurea.
This explains why the trees can only reproduce with human help, by taking cuttings. Just like a mule,B. blakeanais a sterile hybrid.
Hybridisation is when a new species is produced by combining half of the DNA of one species with half of the DNA of another. It is a hit-and-miss exercise. Most of the time, it fails because the two halves of DNA are simply too different to work together. The majority of hybrid embryos never develop.
Even when a hybrid does develop into an adult, they are often sterile.
Bauhinia purpurea has purple flowers Photo: MNS Photo/Alamy
This is because reproducing is probably the most complex thing living organisms do. The two DNA halves might fit together well enough to produce a functional organism, but not well enough to allow for offspring.
We may never know how the original hybrid tree came to be there
Davidson explains this with an analogy. Imagine you have just moved house, and you need a desk in your new home office. But you are short of cash, so you decide to buy two broken second-hand flat-pack desks, and put the pieces together somehow.
"I could probably assemble them into a pretty decent-looking desk, and from the outside, it would look like a desk," Davidson says. But a closer inspection would reveal problems. For instance, the rollout keyboard drawer might not roll out if it "wasn't aligned smoothly".
Bauhinia blakeana is even on Hong Kong's currency Photo: VPC Coins Collection/Alamy
The hybridB. blakeanais the same. It looks like a tree, but not all of it works because its genes are poorly aligned.
In line with this, as far as we know, everyB. blakeanais a genetic clone – a cutting – of the same original plant.
