The botanist who hunts for giant trees at Kew Gardens

In the past decade the scientist has found 25 new large tree species – and he's sure there are more out there

Most botanists hoping to find a plant that has never before been seen have to get on their hands and knees to scour the undergrowth. Not so Xander van der Burgt – he hunts giants.

In the past decade the Kew scientist has found 25 giants unknown to science, trees that soar high into the forest canopy, and he is confident that there are more waiting to be found.

Among the biggest he has identified as new to science is a close relative of the common pea that reaches at least 167ft (51m) high, towering over the UK's tallest oaks.

It may seem that after centuries of scientific endeavour and the spread of humans across the globe that there can be few plants or animals that have gone unnoticed, but Mr van der Burgt and his colleagues at the Royal Botanic Gardens, Kew, have demonstrated there are still big surprises lying in wait.

His biggest discoveries come from the Korup Forest in Cameroon which has proved a rich hunting ground for large, unknown trees.

"In England the diversity is mostly in grasslands, where the plants are mostly 10, 20, 30 or maybe 50 centimetres high. If you stand in the countryside you simply look around and can identify 50 species or more at a time. It's not like that in the tropical forest," he said. "The trees are so large and the leaves are high up – you cannot easily identify the species.

"You have to stand underneath and look up to see the leaves. It can take quite a while even to be able to distinguish which leaves are on which tree. I can spend half an hour looking upwards until I can see the leaves clearly. Then you have to collect samples. Flowers are important to identifying individual species, but it is not easy to find flowering trees. Most tree species flower only a few weeks per year, and they may skip a year. You need fresh flowers, and for that you have to climb."

Local tree-climbers who can scramble up trunks without the need for ropes can be employed for trees up to 100ft, but any higher, and the botanists have to climb up themselves using ropes.

Over the past 15 years, in a test patch of land measuring less than 0.6 square miles, Mr van der Burgt and other botanists have identified 17 big trees unknown to science in the Korup National Park. These include the 167ft relative of the pea, Gilbertiodendron newberyi, with a trunk more than 6ft across.

Having identified 17 confirmed new large tree species in the small plot since 2000, of which six are in the process of being described, he is confident of finding more in the rest of the forest.

"There are dozens of large tree species waiting to be discovered in this area," he said. "There's very little known of them. The local people don't even have names for them. If you scan them for chemicals you might find something of great value to society, either now or in the future. You never know with these unknown trees."

Most of the trees he has discovered are classified as endangered, critically endangered or vulnerable to extinction, with just a handful of each known.