With a few exceptions, alders aredeciduous, and the leaves are alternate, simple, andserrated. Theflowers arecatkins with elongate male catkins on the same plant as shorter female catkins, often before leaves appear; they are mainlywind-pollinated, but also visited by bees to a small extent. These trees differ from thebirches (Betula, another genus in the family) in that the female catkins are woody and do not disintegrate at maturity, opening to release the seeds in a similar manner to manyconifer cones.
The largest species arered alder (A. rubra) on the west coast of North America, andblack alder (A. glutinosa),native to most of Europe and widely introduced elsewhere, both reaching over 30 metres (100 ft). By contrast, the widespreadAlnus alnobetula (green alder) is rarely more than a 5 m-tall (16 ft) shrub.
Speckled alder (Alnus incana subsp.rugosa)—leavesLeaves of the tag alder
Trees with stalked shoot buds, male and female catkins produced in autumn (fall) but stay closed over winter, pollinating in late winter or early spring, about 15–25 species, including:
Shrubs with shoot buds not stalked, male and female catkins produced in late spring (after leaves appear) and expanding and pollinating then, one to four species:
The common namealder evolved from the Old English wordalor, which in turn is derived fromProto-Germanic rootaliso.[10] The generic nameAlnus is the equivalentLatin name, from whence Frenchaulne and SpanishAlamo (Spanish term for "poplar").[10]
Alders are commonly found near streams, rivers, and wetlands. Sometimes where the prevalence of alders is particularly prominent these are calledalder carrs. In thePacific Northwest of North America, thewhite alder (Alnus rhombifolia) unlike other northwest alders, has an affinity for warm, dry climates, where it grows along watercourses, such as along the lowerColumbia River east of the Cascades and the Snake River, including Hells Canyon.
Alder leaves and sometimes catkins are used as food by numerous butterflies and moths.
A. glutinosa andA. viridis are classed as environmental weeds in New Zealand.[11] Alder leaves and especially the roots are important to the ecosystem because theyenrich the soil with nitrogen and other nutrients.
Nitrogen fixation and succession of woodland species
A red alder seed is a tinysamara like those of all alders
Alder is particularly noted for its importantsymbiotic relationship withFrankia alni, anactinomycete,filamentous, nitrogen-fixingbacterium. This bacterium is found inroot nodules, which may be as large as a human fist, with many small lobes, and light brown in colour. The bacterium absorbsnitrogen from the air and makes it available to the tree. Alder, in turn, provides the bacterium withsugars, which it produces throughphotosynthesis. As a result of this mutually beneficial relationship, alder improves thefertility of the soil where it grows, and as apioneer species, it helps provide additional nitrogen for thesuccessional species to follow.
Because of its abundance, red alder delivers large amounts of nitrogen to enrich forest soils. Red alder stands have been found to supply between 130 and 320 kilograms per hectare (120 and 290 pounds per acre) of nitrogen annually to the soil. From Alaska to Oregon,Alnus viridis subsp.sinuata (A. sinuata, Sitka alder or slide alder), characteristically pioneer fresh, gravelly sites at the foot of retreating glaciers. Studies show that Sitka alder, a more shrubby variety of alder, adds nitrogen to the soil at an average rate of 60 kg/ha (54 lb/acre) per year, helping convert the sterile glacial terrain to soil capable of supporting a conifer forest. Alders are common among the first species to colonize disturbed areas from floods, windstorms, fires, landslides, etc. Alder groves often serve as natural firebreaks since these broad-leaved trees are much less flammable than conifers. Their foliage andleaf litter does not carry a fire well, and their thin bark is sufficiently resistant to protect them from light surface fires. In addition, the light weight of alder seeds – numbering 1.5 million per kilogram or 680,000 per pound – allows for easy dispersal by the wind. Although it outgrowscoastal Douglas-fir for the first 25 years, it is veryshade intolerant and seldom lives more than 100 years. Red alder is the Pacific Northwest's largest alder and the most plentiful and commercially important broad-leaved tree in the coastal Northwest. Groves of red alder 25 to 50 centimetres (10 to 20 in) in diameter intermingle with young Douglas-fir forests west of the Cascades, attaining a maximum height of 30 to 33 m (100 to 110 ft) in about sixty years, and then are afflicted byheart rot. Alders largely help create conditions favorable for giant conifers that replace them.[2]
The catkins of some alder species have a degree of edibility,[12] and may be rich in protein. Reported to have a bitter and unpleasant taste, they are more useful for survival purposes. The wood of certain alder species is often used to smoke various food items such ascoffee,salmon, and other seafood.
Alder is notably stable when immersed, and has been used for millennia as a material forpilings for piers and wharves. Most of the pilings that form the foundation ofVenice were made from alder trees.[13]
Alder bark contains the anti-inflammatorysalicin, which is metabolized intosalicylic acid in the body.[14] Some Native American cultures use red alder bark (Alnus rubra) to treat poison oak, insect bites, and skin irritations. Blackfeet Indians have traditionally used an infusion made from the bark of red alder to treat lymphatic disorders andtuberculosis. Recent clinical studies have verified that red alder containsbetulin andlupeol, compounds shown to be effective against a variety of tumors.[15]
Alder is illustrated in the coat of arms for the Austrian town ofGrossarl.
Electric guitars, most notably those manufactured by theFender Musical Instruments Corporation, have been built with alder bodies since the 1950s. Alder is appreciated for its tone that is claimed to be tight and evenly balanced, especially when compared to mahogany, and has been adopted by many electric guitar manufacturers. It usually is finished in opaque lacquer (nitrocellulose,polyurethane, orpolyester), as it does not have a prominent grain.
As ahardwood, alder is used in making furniture, cabinets, and other woodworking products. In these applications, its aforementioned lack of prominent grain means that it is oftenveneered, either by stained light woods such as oak, ash, or figured maple, or by darker woods such as teak or walnut.
Alder bark and wood (likeoak andsweet chestnut) containtannin and are traditionally used to tan leather.
A red dye can also be extracted from the outer bark, and a yellow dye from the inner bark.[17]
^abVít, Petr; Douda, Jan; Krak, Karol; Havrdová, Alena; Mandák, Bohumil (2017). "Two new polyploid species closely related toAlnus glutinosa in Europe and North Africa – an analysis based on morphometry, karyology, flow cytometry and microsatellites".Taxon.66 (3):567–583.doi:10.12705/663.4.
^abcWolfe, J.A. (1966). Tertiary plants from the Cook Inlet region, Alaska (Report). Professional Paper. Vol. 398B. United States Geological Survey. pp. 1–32.doi:10.3133/pp398B.
^Chaney, R.; Axelrod, D. (1959).Miocene Floras of the Columbia Plateau: Part II. Systematic Considerations, by Ralph W. Chaney and Daniel I. Axelrod. Carnegie Institution of Washington. pp. 1–226.Miocene Floras of the Columbia Plateau at theHathiTrust Digital Library
^Wolfe, J. A.; Wehr, W. C. (1987). Middle Eocene dicotyledonous plants from Republic, northeastern Washington (Report). Bulletin. Vol. 1597. United States Geological Survey. pp. 1–25.doi:10.3133/b1597.
^Tilford, Gregory L. (1997).Edible and Medicinal Plants of the West. Mountain Press.ISBN0-87842-359-1.
^Staff (2009)."Bearberry".Discovering Lewis and Clark. The Lewis and Clark Fort Mandan Foundation. Archived fromthe original on 18 December 2010. Retrieved29 April 2011.
^"Native Plant Dyes". United States Department of Agriculture Forest Service. Retrieved17 December 2014.
^PRESSO LA RIVA: L'ONTANO (tr. AT THE SHORE: THE ALDER), December 2015www.officinadellambiente.com, accessed 17 November 2020
^Ontano nero (tr. Black Alder) accessed 17 November 2020uomoenatura.it
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