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Dwarf birch leaves, close-up. The leaves of the dwarf birch tree (Betula nana) are usually dark green (left), but turn to orange (lower right), red and purple in the autumn. The dwarf birch is a miniature perennial, growing to a maximum height of around 0.5 metres. It grows in the Arctic tundra of North America and Asia. Photographed on Clavering Island in North East Greenland National Park, Greenland. (KEYSTONE/SCIENCE PHOTO LIBRARY/SIMON FRASER)