Downy birch extends farther north into the Arctic than any other
broadleaf tree. Specimens of the subarctic populations are usually
small and very contorted, and are often distinguished as "arctic"
downy birch, Betula pubescens subsp. tortuosa (not to be confused
with Betula nana). This subspecies is notable as being one of few
trees native to Iceland and Greenland, where large specimens can
reach 13 metres (43 ft).