Alnus glutinosa (English: black alder, European alder or common alder) is a species of alder in the family Betulaceae, native to most of Europe, including all of the British Isles and Fennoscandia and locally in southwest Asia.
Alnus glutinosa is a tree that thrives in moist soils, and grows under favourable circumstances to a height of 20–30 m, exceptionally up to 37 m, though often less. It is characterized by its 5–10 cm short-stalked rounded leaves 6–12 cm long, becoming wedge-shaped at the base and with a slightly toothed margin. When young they are somewhat glutinous, whence the specific name, becoming later a glossy dark green. As with some other plants, growing near water it keeps its leaves longer than do trees in drier situations. The glossy green foliage lasts after other trees have put on the red or brown of autumn, which renders it valuable for landscape effect. As the Latin name glutinosa implies, the buds and young leaves are slightly sticky with a resinous gum.
The species is monoecious. Flowers are wind-pollinated catkins: the slender cylindrical male catkins are pendulous, reddish in colour and 5–10 cm long; the female are smaller, 2 cm in length and dark brown to black in colour, hard, somewhat woody, and superficially similar to some conifer cones. When the small winged seeds have been scattered the ripe, woody, blackish cones remain, often lasting through the winter. The alder is readily propagated by seeds, but throws up root suckers abundantly.
Important ecological relationships
Alnus glutinosa is most noted for the symbiotic relationship with the bacterium Frankia alni, which forms nodules on the tree's roots. This nitrogen-fixing bacterium absorbs nitrogen from the environment and fixes it into a form available to the tree. In return, the bacterium receives carbon which is produced by the tree through photosynthesis. This relationship, which improves the fertility of the soil environment, has established A. glutinosa as an important pioneer species in ecological succession.
A. glutinosa is also a host to a wide variety of moss and lichen. Some common species found on A. glutinosa include: Tree Lungwort (Lobaria pulmonaria), Stenocybe pullatula, and Menneguzzia terebrata.
It is important as coppice-wood on marshy ground. The alder is capable of enduring clipping as well as marine climatic conditions. The tree may be cultivated as a windbreak. It adapts to the conditions fast and the young trees also develop rapidly, almost growing about one meter or more in a year. Hence, the alder is an outstanding pioneer species for reinstating forestland or abandoned farmland and other problematic soils that do not support vegetation easily. Its rapid growth provides secluded conditions to establish more lasting forest trees. Besides, as nitrogen-fixing bacteria colonize the roots, it is able to enrich the soil and thereby help the proper growth of other plants which cannot cope with the impoverished conditions. Alder also provides shade to the plants growing below and the leaf fall helps to increase the amount of humus present in the soil.
The wood is soft, white when first cut, turning to pale red; the knots are beautifully mottled. Under water the wood is very durable, and it is therefore used for deep foundations of buildings. The supports of the Rialto in Venice, and many buildings in Amsterdam, are of alder wood. Furniture is sometimes made from the wood, as were clogs.
As the wood is soft, flexible, somewhat light, it can be easily worked on as well as split. It is also valued furniture making, wood cuttings, clogs, pencils and bowls. In fact, cabinet makers value this wood very much.
Tanning and dyeing
The bark as well as the young shoots of the alder provides a yellow dye and if you add a tad of copper to it, they provide a yellowish-gray dye. This yellowish-gray dye is useful in half-tones and silhouettes of flesh in tapestry. If the shoots of the alder are cut in March, they will provide a cinnamon colored dye, but when they are dehydrated and powdered, they provide a yellowish-brown or orange shade. On the other hand, freshly cut wood of the alder provides a pinkish-brown or pinkish-fawn coloring, while the catkins provide a green dye. Even the leaves of the alder are used for tanning leather. The dye prepared from the alder leaves is slimy and it is said that if this dye is put out in a room, it will catch fleas on its viscous exterior.
The bark of the alder is combined with copperas (ferrous sulfate) and applied as a foundation for black dyes. When used alone, the bark of the tree dyes woolen clothes giving them a reddish hue called ‘Aldine Red’. The natives of Lapland called Lapps chew the bark of the alder and use the saliva to pigment garments made with leather. You are able to dye a profound boue de Paris with a solution prepared with an ounce of dehydrated and powdered bark of the alder simmered in three-fourth of a pint of water along with an equal proportion of logwood and a solution of six grains of tin, copper and bismuth each and two drops of iron vitriol.
The bark also yields a type of ink as well as an orange-red colorant, while a green pigment is obtained from the catkins of the alder. The fresh green wood yields a pinkish-beige dye, while a yellowish pigment is obtained from the alder bark as well as young branches. However, if the alder shoots are harvested in the month of March, they yield a cinnamon pigment. And when the same shoots are dried and powdered, they provide a yellowish-brown colorant.
The leaves of this tree are sticky in nature and if they are put out in a room, their gelatinous surface will catch flies and fleas.
The bark possesses curative, cathartic, astringent, antipyretic and stimulant or tonic properties. Ingesting the fresh bark may cause nausea and vomiting; hence it is advisable to use dried bark for emetic purposes. Usually, the dehydrated bark of young branches or the inside barks of branches that are about two to three years old are used for therapeutic purposes. Normally, the bark is collected during the spring, dried and then stored for later use.
The dehydrated and powdered form of alder bark is widely used as a constituent of toothpaste, mouthwash and gargle. Many people even chew sticks prepared from the bark as tooth cleaners. A decoction prepared with the bark has a drying action and is useful for tightening the mucous membranes as well as alleviating inflammation. This decoction may also be used to stop internal and external bleeding, and to cure injuries. This decoction is said to heal ague (a fit of shivering or shaking). A medication prepared with the leaves is also an effective wash for scabies. People in Spain curve the leaves of the alder and put them on the soles of aching feet. Herbalists often recommend the alder leaves for nursing mothers to help reduce breast inflammations.
Alpine farmers are said to use the alder leaves to alleviate rheumatism by placing a heated bag full of leaves on the affected areas. Alder leaves are consumed by cows, sheep, goats and horses. However, swine refuse to eat them. According to some people, consumption of alder leaves is harmful to horses, causing blackening of the tongue.
The inside bark boiled in vinegar is effective to eliminate lice as well as treat an assortment of skin conditions, for instance scabs and scabies. The leaves of the alder have astringent properties and are useful as galactagogue (helps in increasing milk yield in humans and animals) and anthelmintic. A decoction prepared with the alder leaves forms an excellent medication to treat breast inflammations in nursing mothers. According to records, ancient herbalists also recommended a decoction of the alder leaves to cure cancer of the face, throat, tongue, duodenum, esophagus, breast, rectum, pancreas, pylorus and uterus. The alder leaves are collected during the summer and always used fresh.
Details of Alder structure and galls
- Trees for Life Species Profile: Alnus glutinosa
- Flora Europaea – Alnus glutinosa
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- Flora of NW Europe: Alnus glutinosa
- British Trees: Alder
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- D'Cruz, Mark. "Ma-Ke Bonsai Care Guide for Alnus glutinosa". Ma-Ke Bonsai. http://makebonsai.com/guide/bonsailink.asp?quicklink=5052&name=Alnus_glutinosa. Retrieved 2011-07-05.
- Clayson, Howell (May 2008). Consolidated list of environmental weeds in New Zealand. Wellington: Department of Conservation. ISBN 978-0-478-14412-3.
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