Carlos Magdalena was prepared for disappointment as he walked into the tropical plants nursery to check on a plant that had consumed several months of his life. The café marron tree was nothing special to look at, but represented a species that was all but extinct in the wild, and he had been working to try to make specimens at Kew Gardens bear seed. So far, nothing had worked.
But that day, early in August this year, something was different. As Magdalena, a first-year horticultural research student, turned away from the plant, a small yellowish-pink lump on one branch caught his eye. It was the café marron's first ever recorded fruit, and another extraordinary success story for the scientists at the micropropagation unit at Kew, a team of botanists who specialise in bringing the most difficult and contrary of plants back from the dead.
Growing rare and fussy species is not easy; forget growing cress on your windowsill. Countless things (water levels, nutrient levels, light levels, and temperature to name but a few) need to be exactly right for some plant to produce fruits and for the seeds in that fruit to germinate and grow properly. Some plants are way beyond the skills of even the most experienced of Kew's horticulturists and this is where the micropropagation unit steps in. This is where gardening meets molecular biology.
The laboratory was set up almost 30 years ago. It deals with plants which are critically endangered in the wild, where there is no way of getting them to reproduce naturally. Many botanical gardens and biological research labs do have facilities for growing plants under controlled conditions but none can carry out the range of experiments going on at Kew.
Having said that, the unit is no complex of gleaming labs and offices. When Viswambharan Sarasan, the lab's tree expert, agrees to show me around, I'm greeted in a modest set of rooms linked by a short corridor. It is small but then there only six full-time scientists at the unit, Sarasan explains.
A door at the end of the corridor leads into the growth room. It is almost uncomfortably bright; fluorescent lights line the underside of every shelf, glaring on to the plants underneath. There are more than 1,000 species of plants at various stages of growth here in spotless glass jars. Each specimen grows in a thick layer of translucent agar jelly filled with nutrients and chemicals tailored to its very specific needs.
And all these plants have one thing in common: they are extremely rare. The café marron is a classic example. First discovered on the island of Rodrigues in Mauritius in 1877, botanists thought that it had become extinct shortly afterwards. They were shocked when, in 1980, a schoolboy looking for rare plants on the island found a specimen of the tree growing by the roadside. When the twig he brought back to his teachers had been identified, botanists hurried out to the tree and found it half-eaten by cattle and suffering from disease. Some cuttings were eventually sent to Kew in the hope that they could somehow save the tree from becoming extinct all over again.
The horticulturists at Kew produced new plants from the cuttings and, two years ago, 11 plants were taken back to Rodrigues to join their wild relative. They are protected from locals - who believe that such a rare plant must cure a host of ailments from venereal disease to hangovers - by three corrugated iron fences.
But producing plants from cuttings did not solve the conservation problems of the café marron: the plants being grown were clones of the original and there was no genetic diversity in the population. They shared all of the original's diseases and it would take just one slightly more hostile bacterium or fungus to wipe out every plant. To ensure its future and increase its genetic diversity, the plant had to be able to reproduce sexually.
To do this, a plant's pollen has to somehow reach its own or another plant's ovules. Normally a bee or some other insect helpfully collects the pollen from one flower and deposits it on the stigma (located between the petals) of a different flower. The pollen then germinates and descends through a tube, called the style, down to the ovules. If fertilisation is successful, the flower becomes a fruit and bears seeds.
But early research on the plant's flowers by Sarasan had shown that, though the pollen and ovules were healthy, the café marron couldn't produce seeds. Producing seeds would also help to get around the disease-causing fungus that had spread inside the branches of the original tree (and had been passed to all its clones). The fungus cannot get into the seed so any plants grown from them would be disease-free.
Without producing seeds, the café marron had no chance of surviving in the wild. "It doesn't happen here because there is an incompatibility," says Sarasan. "Either the stigma is not receiving the pollen at all or the pollen _ is not reaching the ovary."
Sarasan realised that the solution could lie in removing the barriers between the pollen and the ovules. He asked Magdalena to try chopping the styles off several flowers and putting pollen grains on to the ovules. To their amazement, two of the experiments worked and this year the café marron finally bore fruit. Two of the seeds from the fruit were germinated and, three months on, the world's newest café marron trees are standing in a palm-sized petri dish of agar jelly at Kew. Each one is just a few millimetres high.
Since August, Magdalena has tried more than 200 further pollinations but none have produced fruit. Now that he has seen it work, though, he is confident that he will stumble upon the perfect conditions once more. But with the seeds and plants they have already managed to grow, Sarasan will be able to grow thousands of disease-free café marron plants. As the population grows, more trees will be sent back to the island to repopulate the species. The hope is that one day the tree might even be a common sight on Rodrigues.
A cafÀ marron tree is on display in Palm House at Kew Gardens, London.