Alnus

Classification System: APG IV

Superregnum: Eukaryota
Regnum: Plantae
Cladus: Angiosperms
Cladus: Eudicots
Cladus: Core eudicots
Cladus: Rosids
Cladus: Eurosids I
Ordo: Fagales

Familia: Betulaceae
Subfamilia: Betuloideae
Genus: Alnus
Subgenera: A. subg. Alnobetula – A. subg. Alnus – A. subg. Clethropsis
Species: A. acuminata – A. alnobetula – A. betulifolia – A. cordata – A. cremastogyne – A. djavanshirii – A. dolichocarpa – A. fauriei – A. ferdinandi-coburgii – A. firma – A. formosana – A. glutinosa – A. glutipes – A. hakkodensis – A. henryi – A. hirsuta – A. incana – A. japonica – A. jorullensis – A. lanata – A. lusitanica – A. mairei – A. mandschurica – A. maritima – A. matsumurae – A. maximowiczii – A. nepalensis – A. nitida – A. oblongifolia – A. orientalis – A. paniculata – A. pendula – A. rhombifolia – A. rohlenae – A. rubra – A. serrulata – A. serrulatoides – A. sieboldiana – A. subcordata – A. trabeculosa – A. vermicularis

Nothospecies: A. × elliptica – A. × fallacina – A. × hanedae – A. × hosoii – A. × mayrii – A. × peculiaris – A. × pubescens – A. × suginoi

Paleospecies: †A. kluckingi – †A. operia – †A. chaybulakensis
Name

Alnus Mill.

Type species: A. glutinosa (L.) Gaertn.

Synonyms

Heterotypic
Betula-alnus Marshall, Arbust. Amer.: 19 (1785)
Duschekia Opiz, Oekon. Neuigk. Verh. 1839: 524 (1839)
Alnaster Spach, Ann. Sci. Nat., Bot., sér. 2, 15: 200 (1841)
Clethropsis Spach, Ann. Sci. Nat., Bot., sér. 2, 15: 201 (1841)
Type species: non design.
Semidopsis Zumagl., Fl. Pedem. 1: 249 (1849), nom. superfl.
Alnobetula (W.D.J.Koch) Schur, Verh. Mitth. Siebenbürg. Vereins Naturwiss. Hermannstadt 4: 68 (1853), nom. superfl.
Cremastogyne (H.J.P.Winkl.) Czerep., Bot. Mater. Gerb. Bot. Inst. Komarova Akad. Nauk S.S.S.R. 17: 91 (1955)

References
Primary references

Ma, D.D., Li, G.Y. Chen, Z.H. & Xie, W.Y. 2019. Alnus betulifolia (Betulaceae), a New Species from Eastern China. Annales Botanici Fennici 56(4-6), 247-251. DOI: 10.5735/085.056.0409 Reference page.

Additional references

Ohwi, J. 1965. Flora of Japan. 1067 pp. Smithsonian Institution, Washington, D.C. BHL Reference page.
Furlow, J.J. 1979. The systematics of the American species of Alnus (Betulaceae). Rhodora 81(825): 1–121, (826): 151–248. BHL (Part I) (Part II) Reference page.
Furlow, J.J. 1997. Alnus. Pp. - in Flora of North America Editorial Committee (ed.), Flora of North America North of Mexico. Volume 3: Magnoliophyta: Magnoliidae and Hamamelidae. 590 pp. Oxford University Press, New York / Oxford, ISBN 0-19-511246-6. efloras Reference page.
Govaerts, R.H.A. 1995. World Checklist of Seed Plants 1(1, 2). 483, 529 pp. MIM, Deurne. ISBN 90-341-0852-X (issue 1) ISBN 90-341-0853-8 (issue 2). Reference page.
Li, P.C. & Skvortsov, A.K. 1999. Alnus. Pp. 301-304 in Wu, Zh.Y. & Raven, P.H. (eds.), Flora of China. Volume 4: Cycadaceae through Fagaceae. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis, ISBN 0-915279-70-3. efloras PDF Reference page.
Govaerts, R.H.A. 2003. World Checklist of Selected Plant Families Database in ACCESS: 1-216203. The Board of Trustees of the Royal Botanic Gardens, Kew. [unavailable for the public] Reference page.
Iwatsuki, K., Boufford, D.E. & Ohba, H. (eds.) 2006. Flora of Japan IIa: 1-550. Kodansha Ltd., Tokyo. Reference page.
Zare, H. & Amini, T. 2012. A Review of the Genus Alnus Gaertn. In Iran, New Records and New Species. Iranian Journal of Botany 18(1): 10–21. PDF Reference page.
Dimopoulos, P., Raus, Th., Bergmeier, E., Constantinidis, Th., Iatroú, G., Kokkini, S., Strid, A. & Tzanoudakis, D. 2013. Vascular Plants of Greece: An Annotated Checklist. Englera 31: 1–368. Reference page.
Vít, P., Douda, J., Krak, K., Havrdová, A. & Mandák, B. 2017. Two new polyploid species closely related to Alnus glutinosa in Europe and North Africa – An analysis based on morphometry, karyology, flow cytometry and microsatellites. Taxon 66(3): 567–583. DOI: 10.12705/663.4 Reference page.

Links

Govaerts, R. et al. 2020. Alnus in World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the internet. Accessed: 2020 February 11. Reference page.
International Plant Names Index. 2020. Alnus. Published online. Accessed: 11 February 2020.

Vernacular names
Afrikaans: Els
беларуская: Вольха
brezhoneg: Gwern
čeština: Olše
dansk: El-slægten
Deutsch: Erlen
English: Alder
Esperanto: Alno
español: Alisos
eesti: Lepp
euskara: Haltz
suomi: Lepät
Nordfriisk: Elern
français: Aulne
hornjoserbsce: Wólša
magyar: Éger
íslenska: Elri
italiano: Ontano
日本語: ハンノキ属
ქართული: მურყანი
한국어: 오리나무속
коми: Ловпу
Limburgs: Aels
lietuvių: Alksnis
latviešu: Alkšņi
македонски: Евла
эрзянь: Лепе
Nāhuatl: Īlītl
Nedersaksies: Elze
Nederlands: Els
norsk nynorsk: Or
norsk: Oreslekten
polski: Olsza
Runa Simi: Ramran
română: Arinul
русский: Ольха
davvisámegiella: Leaibbit
slovenčina: Jelša
slovenščina: Jelša
српски / srpski: Јова
svenska: Alsläktet
Türkçe: Kızılağaç
українська: Вільха
vèneto: Ònaro
中文: 赤杨

Alders are trees comprising the genus Alnus in the birch family Betulaceae. The genus comprises about 35[2] species 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.[1]

Etymology

The common name alder evolved from the Old English word alor, which in turn is derived from Proto-Germanic root aliso.[3]: alder The generic name Alnus is the equivalent Latin name, from whence French aulne and Spanish Alamo (Spanish term for "poplar").[3]

Description
Pollen

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.

Ecology

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.[4] Alder leaves and especially the roots are important to the ecosystem because they enrich the soil with nitrogen and other nutrients.
Nitrogen fixation and the Succession of woodland species

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.
A red alder seed is a tiny samara like those of all alders

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.[5]

Alder root nodules
An alder root nodule

Whole root nodule
A sectioned alder root nodule

Sectioned root nodules

Parasites

Alder roots are parasitized by northern groundcone.
Uses
Alder coat of arms of Grossarl, Austria

The catkins of some alder species have a degree of edibility,[6] 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.[7]

Alder bark contains the anti-inflammatory salicin, which is metabolized into salicylic acid in the body.[8] 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.[9]

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.[10]

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.[11][12]

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.[13]
Evolutionary history

The oldest fossil pollen that can be identified as Alnus is from northern Bohemia, dating to the late Paleocene, around 58 million years ago.[14]
Classification
A young bull moose browsing on Alnus in Homer, Alaska in 2010
The same spot from the same angle in 2021, the plants are now about 12–15 feet (3.7–4.6 m) in height

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 acuminata Kunth – Andean alder, aliso. Mexico, Central and South America.
subsp. acuminata Kunth
subsp. arguta (Schltdl.) Furlow
subsp. glabrata (Fernald) Furlow
Alnus cordata (Loisel.) Duby – Italian alder. Italy, Corsica.
Alnus cremastogyne Burkill – China.
Alnus firma Siebold & Zucc. – Kyūshū Island in Japan
Alnus glutinosa (L.) Gaertn. – black alder. Europe, Central Asia.
subsp. barbata (C.A.Mey.) Yalt.
subsp. glutinosa (L.) Gaertn.
subsp. incisa (Willd.) Regel
subsp. laciniata (Willd.) Regel
Alnus hirsuta (Spach) Rupr. – Manchurian alder. Japan, Korea, Manchuria, Siberia, Russian Far East

Speckled alder (Alnus incana subsp. rugosa)—leaves

Alnus incana (L.) Moench
subsp. incana (L.) Moench – speckled alder or grey alder. Eurasia, North America
subsp. kolaensis (Orlova) Á.Löve & D.Löve
subsp. rugosa (Du Roi) R.T.Clausen
subsp. tenuifolia (Nutt.) Breitung
Alnus japonica (Thunb.) Steud. – Japanese alder, Japan, Korea, Taiwan, eastern China, Russian Far East
Alnus jorullensis Kunth – Mexican alder. Mexico, Guatemala, Honduras.
subsp. lutea Furlow
subsp. jorullensis Kunth
Alnus matsumurae Callier – Honshū Island in Japan
Alnus nepalensis D.Don – Nepalese alder. Himalayas, Tibet, Yunnan, Nepal, Bhutan, Myanmar, Thailand.
Alnus oblongifolia Torr. – Arizona alder. Arizona, New Mexico, Sonora, Chihuahua
Alnus orientalis Decne. – Oriental alder. Southern Turkey, northwest Syria, Cyprus, Lebanon, Iran
Alnus rhombifolia Nutt. – white alder. California, Nevada, Oregon, Washington, Idaho, Montana
Alnus rubra Bong. – red alder. Alaska, Yukon, British Columbia, California, Oregon, Washington, Idaho, Montana.

Leaves of the tag alder

Alnus serrulata (Aiton) Willd. – hazel alder, tag alder or smooth alder. Eastern North America
Alnus subcordata C.A.Mey. – Caucasian alder. Caucasus, Iran
Alnus tenuifolia Nutt. – thinleaf or mountain alder. Northwestern North America
Alnus trabeculosa Hand.-Mazz. – China, Japan

Subgenus Clethropsis

Trees or shrubs with stalked shoot buds, male and female catkins produced in autumn (fall) and expanding and pollinating then, three species:

Alnus formosana (Burkill) Makino – Formosan alder. Taiwan
Alnus maritima (Marshall) Muhl. ex Nutt. – seaside alder. United States (Georgia, Delaware, Maryland, Oklahoma).
Alnus nitida (Spach) Endl. – Himalayan alder. Western Himalaya, Pakistan, India, Nepal.

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:
Green alder (Alnus viridis)

Alnus alnobetula (Ehrh.) K.Koch
subsp. alnobetula (Ehrh.) K.Koch
subsp. crispa (Aiton) Raus
subsp. fruticosa (Rupr.) Raus
subsp. sinuata (Regel) Raus
subsp. suaveolens (Req.) Lambinon & Kerguélen
Alnus firma Siebold & Zucc. - Kyushu (Japan)
Alnus mandshurica (Callier) Hand.-Mazz. – Russian Far East, northeastern China, Korea
Alnus maximowiczii Callier – Japan, Korea, Russian Far East
Alnus pendula Matsum. - Honshu and Hokkaido (Japan)
Alnus sieboldiana Matsum. - Honshu, Shikoku, and Suwanose-jima (Japan)

Not assigned to a subgenus

Alnus fauriei H.Lév. & Vaniot – Honshu Island in Japan
Alnus ferdinandi-coburgii C.K.Schneid. – southern China
Alnus glutipes (Jarm. ex Czerpek) Vorosch.
Alnus hakkodensis Hayashi – Honshu Island in Japan
Alnus henryi C.K.Schneid. – Taiwan
Alnus lanata Duthie ex Bean – Sichuan Province in China
Alnus mairei H.Lév. – Yunnan Province in China
Alnus paniculata Nakai – Korea
Alnus serrulatoides Callier – Japan
Alnus vermicularis Nakai – Korea

Species names with uncertain taxonomic status

The status of the following species is unresolved:[15]

Alnus balatonialis Borbás
Alnus cuneata Geyer ex Walp.
Alnus dimitrovii Jordanov & Kitanov
Alnus djavanshirii H.Zare – Iran
Alnus dolichocarpa H.Zare, Amini & Assadi – Iran
Alnus figerti Callier
Alnus frangula L. ex Huth
Alnus gigantea Nakai
Alnus glandulosa Sarg.
Alnus henedae Sugim.
Alnus hybrida Rchb.
Alnus laciniata Ehrh.
Alnus lobata Nyman
Alnus microphylla Arv.-Touv.
Alnus obtusifolia Mert. ex Regel
Alnus oxyacantha Lavalle
Alnus subrotunda Desf.
Alnus vilmoriana Lebas
Alnus washinhtonia Wetzel

Hybrids

The following hybrids have been described:[15][16]

Alnus × elliptica Req.—Italy. (A. cordata × A. glutinosa)

Alnus × spaethii
Alnus × fallacina Callier—Ohio, New York State, Vermont, New Hampshire, Maine. (A. incana subsp. rugosa × A. serrulata)
Alnus × hanedae Suyinata—Japan. (A. firma × A. sieboldiana)
Alnus × hosoii Mizush.—Japan. (A. maximowiczii × A. pendula)
Alnus × mayrii Callier—Russian Far East, Japan. (A. hirsuta × A. japonica)
Alnus × peculiaris Hiyama—Kyūshū Island in Japan. (A. firma × A. pendula)
Alnus × pubescens Tausch.—Northern and central Europe. (A. glutinosa × A. incana)
Alnus × suginoi Sugim.—Japan.

The status of the following hybrids is unresolved:[15]

Alnus × aschersoniana Callier
Alnus × koehnei Callier
Alnus × ljungeri Murai
Alnus × purpusii Callier
Alnus × silesiaca Fiek
Alnus × spaethii Callier (A. japonica × A. subcordata)

Fossils

†Alnus heterodonta (Newberry) Meyer & Manchester 1987 – Oligocene fossil, Oregon

References

"World Checklist of Selected Plant Families: Royal Botanic Gardens, Kew". apps.kew.org.
Arno, Stephen; Hammerly, Ramona (2007). Northwest Trees: Identifying and Understanding the Region's Native Trees. Seattle, WA: Mountaineers Books. p. 165. ISBN 978-1-59485-041-7.
"Online Etymology Dictionary". Retrieved 29 March 2019.
Clayson, Howell (May 2008). Consolidated list of environmental weeds in New Zealand. Wellington: Department of Conservation. ISBN 978-0-478-14412-3.
Arno, Stephen; Hammerly, Ramona (2007). Northwest Trees: Identifying and Understanding the Region's Native Trees. Seattle, WA: The Mountaineers Books. pp. 165–69. ISBN 978-1-59485-041-7.
"Plant Search Result, see e.g. Alnus rubra". pfaf.org. Retrieved 17 November 2020.
Nakasako, Eric. "A Look at Venice: Past and Present". Illumin. University of Southern California. Retrieved 22 January 2018.
Ewing, Susan (2012). The Great Alaska Nature Factbook: A Guide to the State's Remarkable Animals, Plants, and Natural Features (2nd ed.). Graphic Arts Books. pp. 106, 142. ISBN 978-0-88240-868-2.
Tilford, Gregory L. (1997). Edible and Medicinal Plants of the West. ISBN 0-87842-359-1.
Staff (2009). "Bearberry". Discovering Lewis and Clark. The Lewis and Clark Fort Mandan Foundation. Archived from the original on 18 December 2010. Retrieved 29 April 2011.
PRESSO LA RIVA: L'ONTANO (tr. AT THE SHORE: THE ALDER), December 2015 www.officinadellambiente.com, accessed 17 November 2020
Ontano nero (tr. Black Alder) accessed 17 November 2020 uomoenatura.it
"Native Plant Dyes". United States Department of Agriculture Forest Service. Retrieved 17 December 2014.
Yang, Xiao‐Yue; Wang, Ze‐Fu; Luo, Wen‐Chun; Guo, Xin‐Yi; Zhang, Cai‐Hua; Liu, Jian‐Quan; Ren, Guang‐Peng (September 2019). "Plastomes of Betulaceae and phylogenetic implications". Journal of Systematics and Evolution. 57 (5): 508–518. doi:10.1111/jse.12479. ISSN 1674-4918.
"The Plant List entry for Alnus". The Plant List, v.1.1. Royal Botanic Gardens, Kew and the Missouri Botanical Garden. September 2013. Retrieved 14 December 2020.

Govaerts R. "Alnus Mill". Plants of the World Online. Board of Trustees of the Royal Botanic Gardens, Kew. Retrieved 14 December 2020.