Everything about Alnus totally explained
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
New World also along the
Andes southwards to
Chile.
Alder
leaves are
deciduous (not
evergreen), 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're 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 don't disintegrate at maturity, opening to release the seeds in a similar manner to many
conifer cones.
Varieties
The best-known species in Europe is the Common or
Black Alder (
A. glutinosa), native to most of
Europe and widely introduced elsewhere. The largest species is
Red Alder (
A. rubra), reaching 35 m (the tallest is 32 m) on the west coast of
North America, with Black Alder and
Italian Alder (
A. cordata) both reaching about 30 m. By contrast, the widespread
Green Alder (
A. viridis) is rarely more than a 5 m shrub.
Uses
Alders establish
symbioses with the
nitrogen-fixing
Actinobacteria Frankiella alni. This bacteria converts atmospheric nitrogen into soil-soluble
nitrates which can be utilised by the alder, and favorably enhances the soil fertility generally. Alders benefit other plants growing near them by taking nitrogen out of the air and depositing it in the soil in usable form; fallen alder leaves make very rich
compost.
Alders are sturdy and fast-growing, even in acidic and damaged sites such as burned areas and
mining sites. Italian Alder is particularly useful on dry, infertile sites. Alders can be used as a producer of simple bio-mass, growing quickly in harsh environments.
Alder catkins are one of the first sources of pollen for
bee species, especially
honeybees, which use it for spring buildup. Alders are also used as a food plant by some
Lepidoptera (
butterfly and
moth) species, see
list of Lepidoptera that feed on alders. Alders are also grown in gardens, and are sometimes made into
bonsai.
Alder is a preferred wood for
charcoal making, formerly used in the manufacture of
gunpowder, or for
smelting metal ores, now used primarily for
cooking. The wood is also traditionally used for
smoking fish and
meat, though this usage has often been replaced by other woods such as
oak and
hickory.
An exception is the smoked
Pacific salmon industry in the
Pacific Northwest, where alder smoking is essentially universal. This is partly due to indigenous traditions of food preservation in the area, and partly because oak, hickory,
mesquite and other woods favored for smoking elsewhere are not locally available in any large quantities. Species used for Pacific salmon smoking are
Red alder A. rubra and to a lesser extent
Sitka alder A. viridis ssp.
sinuata.
Alder is popular as a material for
electric guitar bodies. It is used by many guitar makers, notably the
Fender Guitar Company, who use it on top quality instruments such as the
Stratocaster and
Jaguar. Alder provides a brighter tone than other woods (such as mahogany), and as alder isn't a particularly dense wood it provides a resonant, well-rounded tone with excellent sustain.
Alders are also exceptionally good windbreakers and are planted on the west coast of
Scotland to shelter gardens.
Nitrogen fixation
Alders have root nodules which contain
Frankia sps.,
actinomycete filamentous nitrogen-fixing bacteria. These nodules are found on the roots and may be as large as a human fist, with many small lobes and light brown in appearance.
Word origin
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.
Edibility and Medicinal Uses
Alder catkins are edible and high in protein. Although they're reported to have a bitter and unpleasant taste, they're best remembered for survival purposes. 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.
Classification
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:
Alnus formosana — Formosan Alder Taiwan
Alnus maritima — Seaside Alder. East coastal North America, plus disjunct population in Oklahoma.
Alnus nitida — Himalayan Alder. Western Himalaya.
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:
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.
References and external links
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.
Flora Europaea: Alnus
Flora of Bolivia: Alnus
Flora of China: Alnus
Flora of North America: Alnus
Flora of Pakistan: Alnus
Further Information
Get more info on 'Alnus'.
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