| Alder | |
|---|---|
| Alnus serrulata (Tag Alder) Male catkins on right, mature female catkins left Johnsonville, South Carolina |
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| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Rosids |
| Order: | Fagales |
| Family: | Betulaceae |
| Genus: | Alnus Mill. |
| Species | |
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About 20–30 species, see text. |
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Alder is the common name of a genus of flowering plants (Alnus) belonging to the birch family (Family Betulaceae). The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate Zone and in the Americas along the Andes southwards to Argentina.
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The common name alder is derived from an old Germanic root, also found to be the translation of the Old French "verne" for alder or copse of alders. The botanic name Alnus is the equivalent Latin name. Both the Latin and the Germanic words derive from the Proto-Indo-European root el-, meaning "red" or "brown", which is also a root for the English words elk and another tree: elm, a tree distantly related to the alders.
With few exceptions Alders are deciduous (not evergreen), their 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. They differ from the birches (Betula, the other 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. By contrast, the widespread Green Alder (A. viridis) is rarely more than a 5 m tall shrub.
Alder leaves and sometimes catkins are used as food by numerous butterflies and moths; see List of Lepidoptera that feed on alders.
A. glutinosa and A. viridis are classed as environmental weeds in New Zealand.[1]
Alder is particularly noted for its important symbiotic relationship with Frankia alni, 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 appearance. The bacterium absorbs nitrogen from the air and makes it available to the tree. Alder, in turn, provides the bacterium with carbon, which it produces through photosynthesis. As a result of this mutually-beneficial relationship, alder improves the fertility of the soils where it grows, and as a pioneer species, it helps provide additional nitrogen for the successional species which follow.
The catkins of some alder species have a degree of edibility[2] 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.
Alder bark contains the anti-inflammatory salicin which is metabolized into salicylic acid in the body.[3] Native Americans used Red Alder bark (Alnus rubra) to treat poison oak, insect bites, and skin irritations. Blackfeet Indians 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.[4]
The inner bark of the alder, as well as red osier dogwood, or chokecherry, was also used by Native Americans in their smoking mixtures, known as kinnikinnick, to improve the taste of the bearberry leaf.[5]
Alder is illustrated in the coat of arms for the Austrian town of Grossarl.
Electric guitars, most notably the Fender Stratocaster and Fender Telecaster have been built with alder bodies since the 1950s. Alder is appreciated for its bright tone, and has been adopted by many electric guitar manufacturers.
The genus is divided into three subgenera:
Subgenus Alnus. Trees. Shoot buds stalked. Male and female catkins produced in autumn (fall) but staying closed over winter, pollinating in late winter or early spring. About 15–25 species, including:
Subgenus Clethropsis. Trees or shrubs. Shoot buds stalked. Male and female catkins produced in autumn (fall) and expanding and pollinating then. Three species:
Subgenus Alnobetula. Shrubs. Shoot buds not stalked. Male and female catkins produced in late spring (after leaves appear) and expanding and pollinating then. One to four species:
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