Description and Classification
– Alders are deciduous trees with alternate, serrated leaves.
– The flowers are catkins, wind-pollinated and visited by bees to a small extent.
– Female catkins are woody and do not disintegrate at maturity.
– Red alder and black alder are the largest species, reaching over 30 meters in height.
– Green alder is a shrub, rarely exceeding 5 meters in height.
– The genus Alnus is divided into three subgenera: Alnus, Clethropsis, and Alnobetula.
– Subgenus Alnus includes about 15-25 species, with trees having stalked shoot buds.
– Subgenus Clethropsis consists of three species, with trees or shrubs having stalked shoot buds.
– Subgenus Alnobetula includes shrubs with shoot buds not stalked.
– Some species within Alnus have uncertain taxonomic status.
– Subgenus Alnus includes species like Alnus glutinosa, Alnus incana, and Alnus japonica.
– Subgenus Clethropsis includes species like Alnus formosana, Alnus maritima, and Alnus nitida.
– Subgenus Alnobetula includes species like Alnus viridis and Alnus alnobetula.
– There are also species not assigned to a subgenus, such as Alnus fauriei and Alnus washingtonia.
– Hybrids of Alnus have been described, including Alnus × spaethii and Alnus × elliptica.
Ecology
– Alders are commonly found near streams, rivers, and wetlands.
– They are sometimes called alder carrs when their prevalence is prominent.
– White alder in the Pacific Northwest has an affinity for warm, dry climates.
– Alder leaves and catkins are used as food by numerous butterflies and moths.
– Some species of alders are considered environmental weeds in New Zealand.
Nitrogen fixation and succession of woodland species
– Alders have a symbiotic relationship with Frankia alni, a nitrogen-fixing bacterium.
– The bacterium absorbs nitrogen from the air and provides sugars to the alder.
– Alder improves soil fertility and provides nitrogen for successional species.
– Red alder delivers large amounts of nitrogen to enrich forest soils.
– Alders are pioneer species and help convert sterile terrain to soil capable of supporting a conifer forest.
Uses
– Catkins of some alder species are edible and rich in protein.
– Alder wood is used to smoke coffee, salmon, and other seafood.
– Alder bark contains anti-inflammatory salicin, which is metabolized into salicylic acid.
– Red alder bark is used to treat poison oak, insect bites, and skin irritations.
– Alder is used in smoking mixtures to improve the taste of bearberry leaf.
Parasites and Culture
– Alder roots are parasitized by northern groundcone.
– The movie ‘The Tree of Wooden Clogs’ refers to alder, which is used to make clogs. Source: https://en.wikipedia.org/wiki/Alder
Alders are trees comprising the genus Alnus in the birch family Betulaceae. The genus comprises about 35 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.
| Alder Temporal range: | |
|---|---|
 | |
| Mature Alnus cordata | |
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fagales |
| Family: | Betulaceae |
| Subfamily: | Betuloideae |
| Genus: | Alnus Mill. |
| Type species | |
| Alnus glutinosa (L.) Gaertn. | |
 | |
| Synonyms | |
Genus synonyms
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