Alder (genus)

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The black alder native to Central Europe , near the Aubach in Reichshof (in spring).
Black alder (Alnus glutinosa), immature catkins and old fruit clusters

Black alder ( Alnus glutinosa ), immature catkins and old fruit clusters

Eurosiden I
Order : Beech-like (Fagales)
Family : Birch family (Betulaceae)
Subfamily : Betuloideae
Genre : Alders
Scientific name

The alder ( Alnus ) constitute a genus within the family of birch family (Betulaceae). The approximately 41 species are, with one exception, widespread in the northern hemisphere . There are three species native to Central Europe : the green , gray and black alder .


Branch with winter buds of the black alder ( Alnus glutinosa )
Illustration of the Japanese Alder ( Alnus japonica ) from Forest flora of Japan. Notes on the forest flora of Japan , 1894

Vegetative characteristics

Alder species are deciduous, i.e. deciduous trees or shrubs . Depending on the alder species, a bark is formed or they are classified as periderm tree species; For example, the black alder ( Alnus glutinosa ) forms a deeply fissured, gray-black bark and the gray alder ( Alnus incana ) forms a gray-shiny peridermal surface.

Generative characteristics

Like all birch plants, the alder species are single-sexed ( monoecious ); the inflorescences of both sexes, called catkins , are formed on one specimen . There are only female or male flowers in the catkins. The male flowers sit in pairs and the female flowers in threes in the armpits of bracts . The alder species are the only deciduous trees in which the female catkins lignify and are consequently referred to as cones . Solitary winged or wingless nut fruits are formed.


Gray alder (2 light-colored trunks in the middle) and black alder (darker trunk on the left) socialized in an alder break

Alder species form root nodules at their roots, symbiotically with nitrogen-fixing actinomycetes ( Frankia alni ), similar to the symbiosis of nodule bacteria and legumes . This symbiosis allows alders to live in places that are poor in nutrients. Alder trees can therefore afford to shed their leaves green; alder trees are often pioneer plants in locations that are without vegetation due to natural or human influence (for example, green alders are often pioneer plants after avalanches). They prepare the soil for other plants.

Gray and black alder ( Alnus incana and Alnus glutinosa ) grow mainly on the edges of waters or in wetlands. Very humid locations are often poor in nutrients; At these locations, the nitrogen fixation of the nitrogen- binding root nodules is the decisive reason why only alders thrive there. It is reported that up to 100 kg N / ha and year are added to the soil through the fallen leaves of the alder alone . The gray and black alders often act as bank protection against washout and are considered to be ecologically valuable.

The deciduous leaves of the alder provide a habitat and food for numerous butterfly and butterfly species .


The native to Central Europe alder species are by the apparent fungus Phytophthora alni vulnerable (root rot of alder).


Pollen from alder species contain moderately strong to strong allergens . They have a strong tendency to trigger cross-allergies with birch pollen.

Systematics and distribution

Green Alder ( Alnus alnobetula )
Heart-leaved alder ( Alnus cordata )
Male kittens from Alnus firma
Alder Alder ( Alnus hirsuta )
Japanese alder ( Alnus japonica )
White Alder ( Alnus rhombifolia )
Breeding Spaeth's Alder ( Alnus × spaethii )

The genus Alnus was established in 1754 by the English botanist Philip Miller in The Gardeners Dictionary ... Abridged ... , 4th edition, Volume 1. Betula alnus var. Glutinosa L. was established as the lectotype taxon in 1958 by JJ Swart. Alnus Hill is a homonym . Synonyms for Alnus Mill. Are Betula-alnus Marshall , Semidopsis Zumagl. nom. superflat., Alnobetula (WDJKoch) Schur nom. superflat., Cremastogyne (HJPWinkl.) Czerep. , Duschkia Opiz , Alnaster Spach , Clethropsis Spach .

The approximately 41 species of alder, with the exception of the Andean alder ( Alnus acuminata ), which is native to the Andes of South America , occur exclusively in the northern hemisphere in Eurasia and North America . East of the 115th degree of longitude, however, no tree-like alders can be found in North America. Several species are native to East Asia.

Three species, the green , gray and black alder , are native to Central Europe. The heart-leaved alder ( Alnus cordata ) is common in Corsica and southern Italy .

The alder genus distinguishes around 35 species, which are divided into three sub-genera:

  • Subgenus Alnobetula (WDJKoch) Peterm. : It contains species from North America and Eurasia .
  • Subgenus Alnus : It contains species from Europe, East Asia and the New World.
  • Subgenus Clethropsis (Spach) rule : It contains species from East Asia and the USA.

Here is the complete list of accepted species and natural hybrids according to the World Checklist of Selected Plant Families of the Royal Botanic Gardens in Kew :

A horticultural hybrid is:

  • Spaeth's alder or purple alder ( Alnus × spaethii Callier ) = Alnus japonica × Alnus subcordata

Wood and use

Alder wood is one of the medium-weight types of wood and is easy to work with, hardly cracks when drying, but is only moderately weather-resistant. In the past, alder wood charcoal was used to make gunpowder. Due to its toughness and its deformation-free drying, alder wood is often used in furniture construction as a substitute for cherry, walnut or mahogany wood. Refinements by z. B. Polishing or staining are possible when processing alder wood with smooth surfaces. In addition, this type of wood is often chosen for the construction of percussion instruments (e.g. rattle), stringed or plucked musical instruments.

The black alder can be grown for the production of energy wood or for the production of valuable wood. Alder wood production is a possibility to use nutrient-rich, rewetted fen sites and is therefore also a paludiculture .



  • Peter Schütt (Hrsg.): Lexicon of forest botany . Landsberg / Lech: ecomed 1992, ISBN 3-609-65800-2 , p. 35.
  • Alfons S. Callier : Alnus-forms of the European herbaria and gardens. In: Mitteilungen der Deutschen Dendrologische Gesellschaft , No. 27, 1918, pp. 39–184.
  • Jost Fitschen : Woody flora. Edited by Franz H. Meyer, 10th revised edition, Heidelberg - Wiesbaden: Quelle and Meyer, 1994, ISBN 3-494-01221-0 , pp. 31–1 to 31-4.
  • HG Schlegel: Allgemeine Mikrobiologie , 7th edition, 339, Thieme, Stuttgart, 1992.
  • E. Navarr et al .: Molecular phylogeny of Alnus (Betulaceae), inferred from nuclear ribosomal DNA ITS sequences. In: Plant and Soil; International Journal of Plant Nutrition, Plant Chemistry, Soil Microbiology and Soil-borne Plant Diseases. , Volume 254, 2003, pp. 207-217.

Individual evidence

  1. a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb Rafaël Govaerts (Ed.): Alnus. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved April 13, 2020.
  2. (Mishustin & Shil'nikova, 1966) in JRPostgate: The fundamentals of nitrogen fixation, Cambridge Univ. Press, 1982, p. 151
  3. Philip Miller: The Gardeners Dictionary ... Abridged ... , 4th Edition, Volume 1, 1754.
  4. a b c Alnus at Missouri Botanical Garden, St. Louis, accessed September 18, 2018.
  5. CA Schenk: Foreign forest and park trees (third volume). Paul Parey, Berlin, 1939.
  6. Zhiduan Chen, Jianhua Li: Phylogenetics and Biogeography of Alnus (Betulaceae) Inferred from Sequences of Nuclear Ribosomal DNA ITS Region . In: Chicago Journals - International Journal of Plant Sciences . tape 165 (2) . University of Chicago Press, Chicago 2004, pp. 325-335 .
  7. ^ Alnus in the Germplasm Resources Information Network (GRIN), USDA , ARS , National Genetic Resources Program. National Germplasm Resources Laboratory, Beltsville, Maryland. Retrieved September 17, 2018.
  8. ^ A b Walter Erhardt , Erich Götz, Nils Bödeker, Siegmund Seybold: The great pikeperch. Encyclopedia of Plant Names. Volume 2. Types and varieties. Eugen Ulmer, Stuttgart (Hohenheim) 2008, ISBN 978-3-8001-5406-7 .
  9. Use of alder wood. Retrieved May 24, 2020 .
  10. Oehmke, C. u. Abel, S .: Black Alder (Alnus glutinosa) . In: Wichtmann, W., Schröder, Joosten, H. (Eds.): Paludiculture - cultivation of wet bogs; E. Schweizerbart'sche publishing bookstore . E. Schweizerbart´sche Verlagbuchhandlung, Stuttgart 2016, ISBN 978-3-510-65282-2 , p. 37 .

Web links

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