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Cucumber tree (Dendrosicyos socotrana). This is the only aborescent (tree-shaped) member of the gourd family (Cucurbitaceae), that includes melons, cucumbers and pumpkins. The cucumber tree is endemic to the Socotran archipelago of islands, meaning that it is found nowhere else. This tree evolved to be very large in the absence of large herbivorous (plant-eating) animals, after the islands became isolated from the African mainland some 10 million years ago. Socotra is located in the Indian Ocean at the mouth of the Gulf of Aden, 340 kilometres (km) from mainland Yemen and 250km from the coast of Somalia. (KEYSTONE/SCIENCE PHOTO LIBRARY/DICCON ALEXANDER)