Quick facts

Common name(s): alder, common alder, black alder, European alder

Scientific name: Alnus glutinosa

Family: Betulaceae

Origin: native

Conical in shape, mature trees can reach a height of around 28m and live to approximately 60 years.

The bark is dark and fissured and is often covered in lichen. Twigs have a light brown, spotted stem which turns red towards the top. Young twigs are sticky to touch.

Look out for: small brown cones, which are the female catkins and stay on the tree all year round.

Identified in winter by: female catkins (that look a bit like cones) and purple twigs with orange markings (known as lenticels).

What does alder look like?

A year in the life of an alder tree

Alder leaf close up on a white background

Credit: WTML / Nature Photographers Ltd

Leaves

The purple or grey leaf buds form on long stems and the 3–9cm long, dark green leaves are racquet-shaped and leathery, with serrated edges. The leaf tip is never pointed and is often indented.

Male and female flowers of alder tree, one is long and thin and the other is rounded

Credit: WTML / Nature Photographers Ltd

Flowers

Flowers are on catkins which appear between February and April. Alder is monoecious, which means that both male and female flowers are found on the same tree. Male catkins are pendulous, measuring 2–6cm, and turn yellow. Female catkins are green and oval-shaped and are grouped in numbers of three to eight on each stalk.

Alder tree leaves close up

Credit: Jose Okolo / Alamy Stock Photo

Fruits

Once pollinated by wind, the female catkins gradually become woody and appear as tiny, cone-like fruits in winter. They open up to release their seeds, which are dispersed by wind and water.

Watch alder leaves budding

Not to be confused with:

Hazel (Corylus avellana). The rounded leaf shapes are similar, but hazel leaves are softly hairy compared to the shiny ones of alder.

Child and parent looking at autumn leaves with magnifying glass

Spot the changing seasons

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Did you know?

Alder is the only British native deciduous tree to develop cones.

Where to find alder

Alder is native to almost the whole of continental Europe (except for both the extreme north and south) as well as the United Kingdom and Ireland. Its natural habitat is moist ground near rivers, ponds and lakes and it thrives in damp, cool areas such as marshes, wet woodland and streams where its roots help to prevent soil erosion.

It can also grow in drier locations and sometimes occurs in mixed woodland and on forest edges. It grows well from seed and will quickly colonise bare ground. Because of its association with the nitrogen-fixing bacterium Frankia alni, it can grow in nutrient-poor soils where few other trees thrive.

Worldwide, there are 30 species in the genus Alnus. They are distributed throughout the North Temperate Zone and in North, Central and South America. A. glutinosa is the only species in the genus native to the UK.

Value to wildlife

Alder is the food plant for the caterpillars of several moths including the alder kitten, pebble hook-tip, the autumnal and the blue-bordered carpet moth. Catkins provide an early source of nectar and pollen for bees, and the seeds are eaten by the siskin, redpoll and goldfinch.

The wet conditions found in alder woodland are ideal for a number of mosses, lichens and fungi, along with the small pearl-bordered fritillary and chequered skipper butterflies, and some species of crane fly. Alder roots make the perfect nest sites for otters.

Wildlife that benefits from alder:

Mythology and symbolism

Wet and swampy, alder woods, or carrs, were thought to have a mysterious atmosphere. 

The green dye from the flowers was used to colour and camouflage the clothes of outlaws like Robin Hood, and was thought to also colour the clothes of fairies.

When it’s cut, the pale wood turns a deep orange, giving the impression of bleeding. Because of this, many people feared alder trees and the Irish thought it was unlucky to pass one on a journey.

Did you know?

Much of Venice is built on alder piles, thanks to the durability of its timber in water.

Uses of alder

Soft and porous, alder wood is only durable if kept wet, and its value to humans is down to its ability to withstand rotting in water. Historically, it has been used in the construction of boats, sluice gates and water pipes. These days, alder wood is used to make timber veneers, pulp and plywood.

It is thought that the female woodworm lays eggs in alder in preference to other wood. Traditionally, alder branches were cut and placed in cupboards to deter woodworm from laying eggs in the cupboard timber.

Alder coppices well and the wood makes excellent charcoal and gunpowder. The roots have nitrogen-fixing nodules, conditioning the soil and improving soil fertility on former industrial wasteland and brownfield sites. Alders are also used in flood mitigation.

Alder used to be the preferred wood to make clogs, and it was said that a few alder leaves placed in the shoes before a long journey would cool the feet and prevent swelling.

Threats and conservation

Some alders in the UK have been infected by a type of fungus, Phytophthora. Diseases caused by Phytophthora are quite common on broadleaf tree species. But it was thought to be uncommon on alder until the discovery of a new hybrid strain, which causes root rot and stem lesions.

Sometimes known as alder dieback, the disease is more noticeable in summer as the leaves of affected alders are abnormally small and yellow and often fall early. Infected trees have dead twigs and branches in the crown. They may also bear an unusually large number of cones – a sign of stress. Sometimes the trees die rapidly and other times they deteriorate gradually. Symptoms include bleeding from the bark which resembles brown, rusty spots. When exposed, the reddish, mottled inner bark contrasts with the creamy colour of healthy bark.