Betula pendula, commonly known as silver birch, warty birch, European white birch, or East Asian white birch, is a species of tree in the family Betulaceae, native to Europe and parts of Asia, though in southern Europe it is only found at higher altitudes. Its range extends into Siberia, China and southwest Asia in the mountains of northern Turkey, the Caucasus and northern Iran. It has been introduced into North America, where it is known as the European white birch, and is considered invasive in some states in the United States and in parts of Canada. The tree can also be found in more temperate regions of Australia.

The silver birch is a medium-sized deciduous tree that owes its common name to the white peeling bark on the trunk. The twigs are slender and often pendulous and the leaves are roughly triangular with doubly serrate margins and turn yellow in autumn before they fall. The flowers are catkins and the light, winged seed get widely scattered by the wind. The silver birch is a hardy tree, a pioneer species, and one of the first trees to appear on bare or fire-swept land. Many species of birds and animals are found in birch woodland, the tree supports a wide range of insects and the light shade it casts allows shrubby and other plants to grow beneath its canopy. It is planted decoratively in parks and gardens and is used for forest products such as joinery timber, firewood, tanning, racecourse jumps and brooms. Various parts of the tree are used in traditional medicine and the bark contains triterpenes which have been shown to have medicinal properties.

Description
The silver birch is a medium-sized deciduous tree, typically reaching 15 to 25 m (49 to 82 ft) tall (exceptionally up to 31 metres (102 ft)), with a slender trunk usually under 40 cm (16 in) diameter. The bark on the trunk and branches is golden-brown at first, but later this turns to white as a result of papery tissue developing on the surface and peeling off in flakes, in a similar manner to the closely related Paper birch (B. papyrifera). The bark remains smooth until the tree gets quite large, but in older trees, the bark thickens, becoming irregular, dark and rugged. Young branches have whitish resin warts and the twigs are slender, hairless and often pendulous. The buds are small and sticky, and development is sympodial, that is to say the terminal bud dies away and growth continues from a lateral bud. The species is monoecious with male and female catkins found in the same tree. Some shoots are long and bear the male catkins at the tip, while others are short and bear female catkins. The immature male catkins are present during the winter but the female catkins develop in the spring, soon after the leaves unfurl.

The leaves have short slender stalks and are 3 to 7 cm (1.2 to 2.8 in) long, triangular with broad, untoothed, wedge-shaped bases, slender pointed tips and coarsely double-toothed, serrated margins. They are sticky with resin at first but this dries as they age leaving small white scales. The foliage is a pale to medium green and turns yellow early in the autumn before the leaves fall. In mid-summer, the female catkins mature and the male catkins expand and release pollen, and wind pollination takes place. The small 1 to 2 mm winged seeds ripen in late summer on pendulous, cylindrical catkins 2 to 4 cm (0.8 to 1.6 in) long and 7 mm (0.3 in) broad. The seeds are very numerous and are separated by scales, and when ripe, the whole catkin disintegrates and the seeds are spread widely by the wind.

Silver birch can easily be confused with the similar downy birch (Betula pubescens). Yet, downy birch are characterised by hairy leaves and young shoots whereas the same parts on silver birch are hairless. The leaf base of silver birch is usually a right angle to the stalk while for downy birch it is rounded. In terms of genetic structure the trees are quite different but do, however occasionally hybridise.

Distribution and habitat
The silver birch grows naturally from western Europe eastwards to Kazakhstan, the Sakha Republic in Siberia, Mongolia and the Xinjiang province in China, and southwards to the mountains of the Caucasus and northern Iran, Iraq and Turkey. It is also native to northern Morocco and has become naturalised in some other parts of the world. In the southern parts of its range it is mainly found in mountainous regions. Its light seeds are easily blown by the wind and it is a pioneer species, one of the first trees to sprout on bare land or after a forest fire. It needs plenty of light and does best on dry, acid soils and is found on heathland, mountainsides and clinging to crags. Its tolerance to pollution make it suitable for planting in industrial areas and exposed sites. It has been introduced into North America where it is known as the European white birch, and is considered invasive in the states of Kentucky, Maryland, Washington and Wisconsin. It is naturalised and locally invasive in parts of Canada.
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