|Genus:|| Alnus |
| Alnus glutinosa |
Alders are trees comprising the genus Alnus in the birch family Betulaceae. The genus comprises about 35species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few species extending into Central America, as well as the northern and southern Andes.
The common name alder evolved from the Old English word alor, which in turn is derived from Proto-Germanic root aliso. : alder The generic name Alnus is the equivalent Latin name, from whence French aulne and Spanish Alamo (Spanish term for "poplar").
With a few exceptions, alders are deciduous, and the leaves are alternate, simple, and serrated. The flowers are catkins with elongate male catkins on the same plant as shorter female catkins, often before leaves appear; they are mainly wind-pollinated, but also visited by bees to a small extent. These trees differ from the birches (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 many conifer cones.
The largest species are red alder (A. rubra) on the west coast of North America, and black alder (A. glutinosa), native to most of Europe and widely introduced elsewhere, both reaching over 30 m (100 ft). By contrast, the widespread Alnus alnobetula (green alder) is rarely more than a 5-metre-tall (16-foot) shrub.
Alders are commonly found near streams, rivers, and wetlands. Sometimes where the prevalence of alders is particularly prominent these are called alder carrs. In the Pacific Northwest of North America, the white alder (Alnus rhombifolia) unlike other northwest alders, has an affinity for warm, dry climates, where it grows along watercourses, such as along the lower Columbia 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 and A. viridis are classed as environmental weeds in New Zealand.Alder leaves and especially the roots are important to the ecosystem because they enrich the soil with nitrogen and other nutrients.
Alder is particularly noted for its important symbiotic relationship with Frankia alni , an actinomycete, filamentous, nitrogen-fixing bacterium. This bacterium is found in root nodules, which may be as large as a human fist, with many small lobes, and light brown in colour. The bacterium absorbs nitrogen from the air and makes it available to the tree. Alder, in turn, provides the bacterium with sugars, which it produces through photosynthesis. As a result of this mutually beneficial relationship, alder improves the fertility of the soil where it grows, and as a pioneer species, it helps provide additional nitrogen for the successional 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 to 320 kilograms per hectare (120 to 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 and leaf 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 – 1.5 million per kilogram or 680,000 per pound – allows for easy dispersal by the wind. Although it outgrows coastal Douglas-fir for the first 25 years, it is very shade 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 cm (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 lose vigor as heart rot sets in. Alders largely help create conditions favorable for giant conifers that replace them.
Alder roots are parasitized by northern groundcone.
The catkins of some alder species have a degree of edibility,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 as coffee, salmon, and other seafood.
Most of the pilings that form the foundation of Venice were made from alder trees.
Alder bark contains the anti-inflammatory salicin, which is metabolized into salicylic acid in the body.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 and tuberculosis. Recent clinical studies have verified that red alder contains betulin and lupeol, compounds shown to be effective against a variety of tumors.
The inner bark of the alder, as well as red osier dogwood, or chokecherry, is used by some Indigenous peoples of the Americas in smoking mixtures, known as kinnikinnick, to improve the taste of the bearberry leaf.
Alder is illustrated in the coat of arms for the Austrian town of Grossarl.
Electric guitars, most notably those manufactured by the Fender 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.
As a hardwood, alder is used in making furniture, cabinets, and other woodworking products. For example, in the television series Northern Exposure season 3 episode "Things Become Extinct" (1992), Native American Ira Wingfeather makes duck flutes out of alder tree branches while Ed Chigliak films.
Ermanno Olmi's movie The Tree of Wooden Clogs (L' Albero Degli Zoccoli, 1978) refers in its title to alder, typically used to make clogs as in this movie's plot.
Alder bark and wood (like oak and sweet chestnut) contain tannin 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.
The oldest fossil pollen that can be identified as Alnus is from northern Bohemia, dating to the late Paleocene, around 58 million years ago.
The genus is divided into three subgenera:
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:
Trees or shrubs with stalked shoot buds, male and female catkins produced in autumn (fall) and expanding and pollinating then, three species:
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 status of the following species is unresolved:
The following hybrids have been described:
The status of the following hybrids is unresolved:
Alnus glutinosa, the common alder, black alder, European alder, European black alder, or just alder, is a species of tree in the family Betulaceae, native to 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-sized, 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 flowers in the form of catkins. The small, rounded fruits are cone-like and the seeds are dispersed by wind and water.
Betula pendula, commonly known as silver birch, warty birch, European white birch, or East Asian white birch, is a species of tree in the family Betulaceae, native to Europe and parts of Asia, though in southern Europe, it is only found at higher altitudes. Its range extends into Siberia, China, and southwest Asia in the mountains of northern Turkey, the Caucasus, and northern Iran. It has been introduced into North America, where it is known as the European white birch, and is considered invasive in some states in the United States and parts of Canada. The tree can also be found in more temperate regions of Australia.
Alnus rubra, the red alder, is a deciduous broadleaf tree native to western North America.
Betula nigra, the black birch, river birch or water birch, is a species of birch native to the Eastern United States from New Hampshire west to southern Minnesota, and south to northern Florida and west to Texas. It is one of the few heat-tolerant birches in a family of mostly cold-weather trees which do not thrive in USDA Zone 6 and up. B. nigra commonly occurs in floodplains and swamps.
Alnus incana, the grey alder or speckled alder, is a species of tree in the birch family, with a wide range across the cooler parts of the Northern Hemisphere.
Alnus jorullensis, commonly known as Mexican alder, is an evergreen or semi-evergreen alder, native to eastern and southern Mexico, Guatemala and Honduras. Although previously reported from the Andes, further collections showed these to be the similar species Alnus acuminata, commonly found in South America.
Alnus cordata, the Italian alder, is a tree or shrub species belonging to the family Betulaceae, and native to the southern Apennine Mountains and the north-eastern mountains of Corsica. It has been introduced in Sicily and Sardinia, and more recently in Central-Northern Italy, other European countries and extra-European countries, where it has become naturalised.
Alnus nepalensis is a large alder tree found in the subtropical highlands of the Himalayas. The tree is called Utis in Nepali and Nepalese alder in English. It is used in land reclamation, as firewood and for making charcoal.
Alnus subcordata, the Caucasian alder, is a species in the family Betulaceae, native to Hyrcanian forests of Iran and the Caucasus. It is closely related to the Italian alder and Alnus orientalis.
Mountain alder is a common name for two different alders:
Alnus rhombifolia, the white alder, is an alder tree native to western North America, from British Columbia and Washington east to western Montana, southeast to the Sierra Nevada, and south through the Peninsular Ranges and Colorado Desert oases in Southern California. It occurs in riparian zone habitats at an altitudes range of 100–2,400 metres (330–7,870 ft). While not reported in northern Baja California, it has been predicted on the basis of its climatic adaptation to occur there also. Alnus rhombifolia is primarily found in the chaparral and woodlands, montane, and temperate forests ecoregions.
Alnus acuminata is a species of deciduous tree in the Betulaceae family. It is found in montane forests from central Mexico to Argentina.
Arocatus roeselii is a species of lygaeid bug.
Bucculatrix cidarella is a moth of the family Bucculatricidae. It is found in most of Europe, Kazakhstan and Japan (Honshu). It was described in 1839 by Philipp Christoph Zeller.
Caloptilia alnivorella, the alder leafminer, is a moth of the family Gracillariidae. The species was first described by Vactor Tousey Chambers in 1875. It is known from the Russian Far East, Canada and the United States.
Frankia alni is a Gram-positive species of actinomycete filamentous bacterium that lives in symbiosis with actinorhizal plants in the genus Alnus. It is a nitrogen-fixing bacterium and forms nodules on the roots of alder trees.
Alnus serrulata, the hazel alder or smooth alder, is a thicket-forming shrub in the family Betulaceae. It is native to eastern North America and can be found from western Nova Scotia and southern New Brunswick south to Florida and Texas.
Alnus alnobetula is a common tree widespread across much of Europe, Asia, and North America. Many sources refer to it as Alnus viridis, the green alder, but botanically this is considered an illegitimate name synonymous with Alnus alnobetula subsp. fruticosa.
Eriophyes laevis is a gall mite which makes small, pimple-like galls on the leaves of alder. The mite was first described by the Austrian zoologist, Alfred Nalepa in 1889 and is found in Europe and North America.
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