{{redirect|Alder}}
{{Taxobox
| color = lightgreen
| name = Alder
| image = Tagalder8139.jpg
| image_width = 250px
| image_caption = ''Alnus serrulata'' (Tag Alder)<br />Male catkins on right,<br />mature female catkins left<br />[[Johnsonville, South Carolina]]
| regnum = [[Plant]]ae
| divisio = [[flowering plant|Magnoliophyta]]
| classis = [[dicotyledon|Magnoliopsida]]
| ordo = [[Fagales]]
| familia = [[Betulaceae]]
| genus = '''''Alnus'''''
| genus_authority = [[Philip Miller|Mill.]]
| subdivision_ranks = Species
| subdivision =
About 20-30 species, see text.
}}

'''Alder''' is the common name of a [[genus]] of [[flowering plant]]s ('''''Alnus''''') belonging to the [[birch]] family (Family [[Betulaceae]]). The genus comprises about 30 [[species]] of [[Plant sexuality|monoecious]] [[tree]]s and [[shrub]]s, few reaching large size, distributed throughout the North Temperate zone, and in the [[New World]] also along the [[Andes]] southwards to [[Chile]].

Alder [[leaf|leaves]] are [[deciduous]] (not [[evergreen]]), alternate, simple, and serrated. The [[flower]]s are [[catkin]]s 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 [[bee]]s to a small extent. They differ from the [[birch]]es (''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 cone]]s.

==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==
[[Image:Alder female 8519.JPG|left|thumb|''Alnus serrulata'' (Tag Alder), female catkins, [[Johnsonville, South Carolina]]]]
Alders establish [[symbiosis|symbioses]] with the [[nitrogen]]-fixing [[Actinobacteria]] ''Frankiella alni''. This bacteria converts atmospheric nitrogen into soil-soluble [[nitrate]]s 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 [[honeybee]]s, which use it for spring buildup. Alders are also used as a food plant by some [[Lepidoptera]] 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]] [[ore]]s, now used primarily for [[cooking]]. The wood is also traditionally used for [[smoking (food)|smoking]] [[fish]] and [[meat]], though this usage has often been replaced by other woods such as [[oak]] and [[hickory]].

An exception is the smoked [[Oncorhynchus|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 [[Green Alder|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 Musical Instruments Corporation|Fender]] Guitar Company, who use it on top quality instruments such as the [[Stratocaster]] and [[Fender Jaguar|Jaguar]]. Alder provides a brighter tone than other woods (such as mahogany), and as alder is not 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.{{Fact|date=April 2007}}

==Word origin==
The common name ''alder'' is derived from an old [[Germanic language|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 language|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.

==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:
*''[[Alnus acuminata]]'' — Andean Alder. Andes Mountains, South America.
*''[[Alnus cordata]]'' — Italian Alder. Italy.
*''[[Alnus cremastogyne]]''
*''[[Alnus glutinosa]]'' — Black Alder. Europe.
[[Image:Alnus incana rugosa leaves.jpg|right|thumb|Speckled Alder (''Alnus incana'' subsp. ''rugosa'') — leaves]]
*''[[Alnus incana]]'' — Grey Alder. Eurasia.
**''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.
*''[[Alnus nepalensis]]'' — Nepalese Alder. Eastern Himalaya, southwest China.
*''[[Alnus orientalis]]'' — Oriental Alder. Southern Turkey, northwest Syria, Cyprus.
*''[[Alnus rhombifolia]]'' — White Alder. Interior western North America.
*''[[Alnus rubra]]'' — Red Alder. West coastal North America.
[[Image:Alnus serrulata leaves.jpg|right|thumb|Leaves of the [[Tag Alder]]]]
*''[[Alnus serrulata]]'' — Hazel alder, Tag Alder or Smooth alder. Eastern North America.
*''[[Alnus subcordata]]'' — Caucasian Alder. Caucasus, Iran.

'''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:
[[Image:Alnus-viridis.JPG|right|thumb|Green Alder (''Alnus viridis'')]]
*''[[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==
{{Wiktionary|alder}}
*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.
*[http://rbg-web2.rbge.org.uk/cgi-bin/nph-readbtree.pl/feout?FAMILY_XREF=&GENUS_XREF=Alnus&SPECIES_XREF=&TAXON_NAME_XREF=&RANK= Flora Europaea: ''Alnus'']
*[http://www.efloras.org/florataxon.aspx?flora_id=40&taxon_id=101157 Flora of Bolivia: ''Alnus'']
*[http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=101157 Flora of China: ''Alnus'']
*[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=101157 Flora of North America: ''Alnus'']
*[http://www.efloras.org/florataxon.aspx?flora_id=5&taxon_id=101157 Flora of Pakistan: ''Alnus'']
[[Category:Alnus| ]]
[[Category:Betulaceae]]

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[[es:Alnus]]
[[eo:Alno]]
[[eu:Haltz]]
[[fr:Aulne]]
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[[ka:მურყანი]]
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[[pt:Alnus]]
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[[ru:Ольха]]
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[[simple:Alder]]
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