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Below, on the rocky, exposed ridges and sheltered valleys of the limestone plateau grow exotic succulent trees. These include the Soqotran Fig (Dorstenia gigas) and the Desert Rose (Adenium obesum subsp. sokotranum). Their swollen bottle-shaped trunks keep the trees supplied with water during the summer droughts. Other plants in this habitat, such as a relative of the bluebell (Ledebouria grandifolia)-recently discovered in flower for the first time cope with summer drought by hiding underground as bulbs until the rains begin.

Ledebouria grandifolia: © Royal Botanic Garden Edinburgh Soqotra sports examples of gigantism -a curious phenomenon of island evolution. Until 10 million years ago, when the island was still part of Africa, any broad-trunked trees would have been destroyed by large herbivores like elephants and rhinoceroses. When Soqotra broke away the absence of such herbivores and trees left a new ecological niche into which herbs and shrubs could grow, and grow. The most startling example of gigantism is the cucumber tree (Dendrosicyos Soqotrana), found on the coastal plain. Most other members of the cucumber family are climbing plants or shrubs, but their Soqotran cousin is a tree, up to four metres high with a bottle-shaped trunk and cucumbers hanging from its branches.

Soqotra has been famous for its botanical riches for hundreds of years. As well as cinnabar, other products exported to the ancient Mediterranean region included resins of the local Frankincense (Boswellia) and Myrrh (Commiphora) trees, used in medicines and rituals, and the juice of the native Bitter Aloe (Aloe perryi), used as a purgative. By the 19th century news of Soqotra's rich flora had reached the British Association for the Advancement of Science in London.

Aloe perryi: © Royal Botanic Garden Edinburgh In 1880 the Association launched the first ever scientific expedition to the island, led by the Scottish botanist Isaac Bayley Balfour who put Soqotra on the map. In seven weeks Balfour collected more than 500 plant species, over 200 of which were new to science. But by 1967 a group of British botanists visiting the island came away believing that most species faced imminent extinction fro increasing human activity. If unchecked goat-grazing and wood-cutting woul rapidly destroy the natural vegetation So many botanists gave up hope for th flora and visits to the island dropped.

Then in 1985 the island botanis Quentin Cronk resurveyed Soqotra an found that the predictions of earlie scientists had been too pessimistic. Although there were still large herds o livestock and extensive wood-cutting, the environment was largely unspoilt. "Having seen the degradation overgrazing can cause," says Cronk, "I was staggered to come across a place which was in all probability substantially the same now as 1000 years ago." His discovery revived international scientific interest in Soqotra. Specialists in Arabian flora have found many new species and traced almost all the previously recorded flora, including the only Soqotran plant officially recorded as extinct by the World Conservation Union, the pink-flowered shrub, Taverniera sericophylla.