Alder is the common name of a genus of ( Alnus) belonging to the birch family Betulaceae. The genus comprises about 30 species of monoecious and , a few reaching a large size, distributed throughout the north temperate zone.
The common name "alder" evolved from Old English "alor", which in turn is derived from Proto-Germanic
aliso. The generic name Alnus
is the equivalent Latin
name. Both the Latin and the Germanic words derive from the Proto-Indo-European
, 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 a few exceptions, alders are deciduous
, and the leaves are alternate, simple, and serrated
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
, 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
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 Alnus viridis (green alder) is rarely more than a 5-m-tall shrub.
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.
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Alder is particularly noted for its important symbiotic
relationship with Frankia alni
, an actinomycete
, nitrogen-fixing bacterium
. This bacterium is found in
, 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
, 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 which follow.
Alder roots are parasitized by northern groundcone
The of some alder species have a degree of edibility,
[ Plants For A Future (Database)] 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, especially 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.
[Ewing, Susan. The Great Alaska Nature Factbook. Portland: Alaska Northwest Books, 1996.] 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. [Edible and Medicinal Plants of the West, Gregory L. Tilford, ISBN 0-87842-359-1]
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.
[Staff (2009) "Bearberry" Discovering Lewis and Clark The Lewis and Clark Fort Mandan Foundation]
Alder is illustrated in the coat of arms for the Austrian town of Grossarl.
Electric guitars, most notably the Fender Jazz Bass, Fender Precision Bass, Fender Stratocaster and Fender Telecaster, have been built with alder bodies since the 1950s. Alder is appreciated for its claimed tight and even balanced tone, 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 1992 season 3 episode "Things Become Extinct", Native American Ira Wingfeather makes duck out of Alder tree branches while Ed Chigliak films.
The genus is divided into three subgenera:
Subgenus Alnus: 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:
Alnus incana—grey alder, Eurasia
Alnus hirsuta ( A. incana subsp. hirsuta)—Manchurian alder, northeastern Asia, and central Asia in mountains
Alnus oblongifolia ( A. incana subsp. oblongifolia)—Arizona alder, southwestern North America
Alnus rugosa ( A. incana subsp. rugosa)—speckled alder, northeastern North America
Alnus tenuifolia ( A. incana subsp. tenuifolia)—thinleaf or mountain alder, northwestern North America
Alnus japonica—Japanese alder, Japan
Alnus jorullensis—Mexican alder, Mexico, Guatemala (one of the few evergreen species)
Alnus mandshurica— Russian Far East, China, Korea
Alnus matsumurae—Honshū (Japan)
Alnus nepalensis—Nepalese alder, eastern Himalaya, southwest China
Alnus orientalis—Oriental alder, southern Turkey, northwest Syria, Cyprus
Alnus pendula—Japan, Korea
Alnus rhombifolia—white alder, interior western North America
Alnus rubra—red alder, west coastal North America
Subgenus Clethropsis. Trees or shrubs with stalked shoot buds, male and female catkins produced in autumn (fall) and expanding and pollinating then, three species:
Subgenus Alnobetula. 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:
Alnus viridis—green alder, widespread:
Alnus viridis subsp. viridis - Eurasia
Alnus viridis subsp. maximowiczii ( A. maximowiczii) - Japan
Alnus viridis subsp. crispa ( A. crispa) - northern North America
Alnus viridis subsp. sinuata ( A. sinuata, Sitka alder or slide alder - western North America, far northeastern Siberia
Chen, Zhiduan and Li, Jianhua (2004). Phylogenetics and Biogeography of Alnus (Betulaceae) Inferred from Sequences of Nuclear Ribosomal DNA ITS Region. International Journal of Plant Sciences 165: 325–335.