Socotra has been alone in the Arabian Sea off Yemen for so long that a third of its plants grow only here. The one everybody comes to see looks like an umbrella turned inside out, and it bleeds red when you cut it. On the Diksam plateau the dragon's blood trees stand in loose forests on open red rock, some right at the rim of the canyons with nothing but air behind them. At the end of the day each crown flattens into a black umbrella against an orange sky, the canyon below filling with shadow. Under an older tree the branches close into a roof thick enough to lay a clean circle of shade at your feet. The packed crown is a tool: it combs moisture out of the mountain mist and runs it down the trunk. The shade and drip beneath let other plants take hold, so each tree waters its own ground.
A guide scores the pale bark and the resin seeps out thick and crimson, drying to hard dark-red beads in your palm. It has been traded for thousands of years as dye and medicine, and the traders who carried it took the red drops for a dragon's blood. Away from the plateau the island changes fast: the granite Haghier peaks catch the clouds, and cold streams gather in their rock pools. At Arher white sand has piled hundreds of metres up a wall of dark cliffs, and a cold stream runs down through the dunes into the sea. On Homhil a natural rock pool sits at the lip of a cliff, desert roses round its rim and the coast far below you. The forests themselves are going: goats eat the seedlings, recent cyclones have flattened thousands of century-old trees, and the groves have thinned by nearly half in a century. The isolation was never total. Three kilometres inside Hoq Cave, past forests of stalagmites and pools of still water, the walls carry inscriptions scratched by sailors two thousand years ago. Socotra was a stop on the run between Africa, Arabia and India.