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 was handed 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 flower in question is a peculiar plant known as the Hong 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 by Jean-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 scientist Rob Davidson of the journal Gigascience. 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.
"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 of grafting is a reminder of how different plants are from animals.
Some years after Delavay's discovery, a cutting was passed to what is now the Hong Kong Zoological and Botanical Gardens. There it was named Bauhinia 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. Today B. blakeana is anything but rare.
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 actually a hybrid of two known species; the pink-flowered butterfly tree (B. variegata),and the purple-flowered B. purpurea.
This explains why the trees can only reproduce with human help, by taking cuttings. Just like a mule, B. blakeana is 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.
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".
The hybrid B. blakeana is 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, every B. blakeana is a genetic clone – a cutting – of the same original plant.
We may never know how the original hybrid tree came to be there. But scientists are now using modern genomic techniques to understand the orchid tree better.
Because B. blakeana is a sterile hybrid, it is in grave danger
Davidson is leading a crowd-funded project called Bauhinia Genome, which has so far raised over $2,600 to sequence the plant's unique genome. "We were hearing all the time that genetic sequencing is getting cheaper and cheaper," he says. In late 2016 the project released its first batch of data, covering the "active" parts of the genome.
The project doubles as a public education initiative, aiming to teach people about genome sequencing. "I don't think a scientific paper's ever been written in local Cantonese," says Davidson. His project will produce videos, articles and peer-reviewed papers in both English and Cantonese. "We want to make it as accessible as possible."
The team also asked the public to go out and look for B. blakeana trees to help map their distribution. "Hiking is very popular in Hong Kong, and we wanted to have people going out and looking at the trees, getting to know the differences between their Bauhinia and the two parent Bauhinia species," Davidson says.
But there is also a serious side to the project. Because B. blakeana is a sterile hybrid, it is in grave danger.
Every single one of the 25,000 cuttings in Hong Kong, and the other trees around the world, are all genetically identical. They are all clones of each other, with no genetic diversity. This genetic homogeneity is not a good thing.
The orchid tree has already been hit by several fungal diseases in recent years
Trees, just like animals, can contract diseases caused by fungal, viral or bacterial infections. These diseases can be devastating: Dutch elm disease has killed over 25 million trees in the UK alone, and ash dieback threatens to wipe out ash trees across Europe.
But the situation could be even more serious for clonal plants like B. blakeana. Normally, "for those kinds of diseases, you find that there are some plants, some members of the species that have a natural resistance, because of their biodiversity," says Davidson. "But in the case of this plant, they're all the same."
That means they are sitting ducks. "If there was an infection that was very effective at killing off these trees, they would all be wiped out," says Davidson.
The orchid tree has already been hit by several fungal diseases in recent years, and Davidson hopes that his genome-sequencing project might give it a chance to fight back against future infections.
"We hope that by mapping the genome we could perhaps use that, if there was some kind of infestation that happened further down the line," says Davidson.
When an organism reproduces sexually, it wipes the slate clean in terms of ageing
"You can sequence a new parasite or bacterium quite quickly, so if you already had a map of the Bauhinia genome, then you could compare the two," he says. This could enable scientists to figure out how the infection was able to attack B. blakeana, and quickly engineer a counter-measure.
Another solution to the problem of low genetic diversity would be to repair B. blakeana's reproductive system, allowing the plants to reproduce sexually. Kick-starting their evolution like this would give them a fighting chance against future infections.
Fertility would also help the Hong Kong orchid tree avoid another potential peril of clonal reproduction: ageing.
When an organism reproduces sexually, it wipes the slate clean in terms of ageing. A new-born organism, produced by sex, has none of the age-related damage its parents do.
It may be only a matter of time before the trees start dying of old age
Without this step, the Hong Kong orchid tree may be ageing continuously, with each cutting carrying on from the age of the cut tree.
Trees are notorious for being exceptionally long-lived compared to animals, with the oldest living trees some 4,000 years old, so it may be some time before this problem becomes apparent. Little is known about ageing in clonal plants like Bauhinia, but studies suggest that signs of ageing are visible in long-lived trembling aspen (Populus tremuloides), which reproduce clonally.
If B. blakeana's cells are ageing generation after generation, it may be only a matter of time before the trees start dying of old age.
Lawrence Ramsden of the University of Hong Kong was a member of the team that discovered B. blakeana's hybrid origin in 2005. He is now leading a search for mutant trees that are fertile. Such trees might exist: with a few mutations in the right places, a sterile B. blakeana could theoretically start producing viable seeds.
It is such a beautiful and emblematic flower
If they do find a fertile B. blakeana tree, it might not be quite as beautiful as the sterile ones. That is because the flowers of sterile B. blakeana trees "stay in bloom longer because the plant doesn't put any energy into producing seeds," says Davidson.
However, a fertile tree might just save the species. But until one is found, or one of the other approaches comes to fruition, the Hong Kong orchid tree will have to survive the way it has for the last century.
The orchid tree was chosen as Hong Kong's emblem because it represents the merging of old and new. So it seems apt that the plant is itself a hybrid, and that it might be saved by melding new technology with old-fashioned amateur naturalism.
"It is such a beautiful and emblematic flower," says Davidson.
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