Birch trees come in many 'flavours', but two are relatively common in the UK - Silver (Betula pendula) and Downy (Betula pubescens). The dwarf birch (Betula nana) can be found in the Highlands of Scotland.
Birch species readily hybridise.
They are relatively short lived trees, which are quick to colonise open areas: they are a pioneer species. After the last Ice Age, they were amongst the first species to colonise the UK.
Simple leaf that is roughly triangular with rounded corners and a leaf margin that is quite toothed (serrated). The leaves have a petiole or leaf stalk. The leaves of the downy birch are rounder in shape than those of silver birch.
The leaves of silver birch are more noticeably serrated - even the teeth may have teeth!
Birch leaves are a source of food for various butterflies.
Buds, Bark & Stem
The young twigs of downy birch have small hairs, whereas the silver birch twigs have small white wart like structures. The buds are quite prominent on the slender twigs and may be sticky.
Dried pieces of bark are excellent for lighting a campfire.
The bark is usually bright in colour, from red on very young stems to becoming white/silver with age. It then develops dark grey/black ‘arrows and diamonds’ or horizontal streaks of grey in the case of downy birch. Consequently older trees have a much darker trunk and bark.
The bark is characterised by the long, horizontal lenticels (for gas exchange).
Flowers and Fruits
Birch trees have separate male and female flowers, that is, they are monoecious. The flowers appear at the same time as the new leaves in the spring.
The male flowers are drooping catkins, about 3 cm long. The pollen can be a problem to hay fever sufferers. Female flowers are upright and between 1 and 2cm tall. The flowers are wind pollinated.
The pollinated female flowers elongate and form hanging catkins. These contain hundreds of minute seeds, which are dispersed on the wind.
In the past, bundles of birch twigs were used for corporal punishment. Birch trees may also develop witches' brooms. A witch's broom is an abnormal growth of the twigs (that may resemble a besom - a broom made from a bundle of twigs or it may be a ball like structure).
The wood of birch is quite fine grained and pale in colour.