Trees & Shrubs – The Alder – Alnus glutinosa

Trees & Shrubs – The Alder – Alnus glutinosa

Alnus glutinosa, the common alder, black alder, European alder or just alder, is a species of tree in the family Betulaceae, native to Britain, most of Europe, southwest Asia and northern Africa. It thrives in wet locations where its association with the bacterium Frankia alni enables it to grow in poor quality soils. It is a medium size, short-lived tree growing to a height of up to 30 metres (100 ft). It has short-stalked rounded leaves and separate male and female flower in the form of catkins. The small, rounded fruits are cone-like and the seeds are dispersed by wind and water.

The common alder provides food and shelter to wildlife, with a number of insects, lichens and fungi being completely dependent on the tree. It is a pioneer species, colonising vacant land and forming mixed forests as other trees appear in its wake. Eventually common alder dies out of woodlands because the seedlings need more light than is available on the forest floor. Its more usual habitat is forest edges, swamps and riverside corridors. The timber has been used in underwater foundations and for manufacture into paper and fibreboard, for smoking foods, for joinery, turnery and carving. Products of the tree have been used in ethnobotany, providing folk remedies for various ailments, and research has shown that extracts of the seeds are active against pathogenic bacteria.

The Alder (Alnus glutinosa).

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London Tree Surgeons – The common alder tree in summer.
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the same alder tree in the winter

Edward Step, on The Alder — or common alder

Although the Alder is abundant by riversides and in all low-lying moist lands as far north as Caithness, it is not so generally well known at sight as the Oak, the Beech, and the Birch. It is a small tree ordinarily only thirty to forty feet in height, with a girth from three to six feet, though occasionally it aspires to seventy feet in height. This is when it is growing in moist loam, upon which rain or floods have washed down good layers of humus from woods at a higher elevation. If, with its roots thus well cared for, its head is in a humid atmosphere, the Alder is in happy case. If it has had the misfortune to get into a porous soil, though this may be moist enough to please an Ash, the Alder becomes merely a big bush.

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leaf of the common alder


The bark of the Alder is rough and black, and the wood soft. Whilst the tree is alive its wood is white, but when cut and exposed to the air it becomes red; finally, on drying, it changes to a pinkish tint. As timber it has no great reputation, except for piles or other submerged purposes, when it is said to be exceedingly durable. It has also enjoyed a great reputation for making the best charcoal for the gunpowder mills, and it is largely used by the turner, the wood-carver, and the cabinet-maker. The leaves, which have short stalks, and are from two to four inches long, are roundish with a wedge-shaped base. They have a waved and toothed margin, and remain green long after the leaves of other trees have fallen. In their young condition these leaves are covered with hairs, and are sticky to the touch, and it is to this fact that the name glutinosa has reference.

The flowering of the Alder is very similar to that of the Birch, but the male catkins have red scales, and each flower four stamens. The female spikes have the fleshy scales covered by red-brown bracts of a woody consistence, which persist after the fruit has dropped out of them. Seed is not produced until the Alder is twenty years old, and the crop is repeated almost every year after. The cones are ripe about October or November, when they scatter their fruit, but the empty ones persist in hanging to the branches throughout the winter in numbers sufficient to give the leafless tree a brown appearance from a little distance. The immature male catkins are in evidence at the same time.

There is a variety (incisa) of the Alder in which the leaves are so deeply toothed that they bear a close resemblance to those of the Hawthorn.

In some localities the tree is called the Howler and Aller, the latter word apparently the original name, for its Anglo-Saxon forms were ælr, alr, and aler.

Catkins of Alder.

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catkins of the common alder tree


Bole of Alder. The trunk of the common alder tree.

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the bole or trunk of the common alder tree



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