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:This article is about the tree. For other uses of the name, see Alder (disambiguation)
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. The leaves are deciduousDeciduous means "temporary" or "tending to fall off". Deciduous plants are those that lose their foliage for part of the year. In most cases, the foliage loss coincides with the incidence of winter in temperate or polar climates, but some plants lose thei, simple, and serrated. The flowerA flower is the reproductive organ of those plants classified as angiosperms ( flowering plants; Division Magnoliophyta). The function of a flower is to produce seeds through sexual reproduction''. For the higher plants, seeds are the next generation, ands 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 beeThis article is about the insect. For the character B, see B. Andrenidae Anthophoridae Apidae Colletidae Ctenoplectridae Halictidae Heterogynaidae Megachilidae Melittidae Oxaeidae Sphecidae Stenotritidae Bees Apoidea superfamily) are flying insects, closes to a small extent. They differ from the birchmany species ''see text and classification Birch is the name of any tree of the genus Betula in the family Betulaceae, closely related to the beech/ oak family, Fagaceae. These are generally small to medium-size trees or shrubs, mostly of northern temperaes (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 cones.
The best-known species is the Common or Black alder (A. glutinosa), native to most of EuropeFor the band of the same name, see Europe (band . Europe is a continent forming the westermost part of the Eurasian supercontinent. Europe is bounded to the north by the Arctic Ocean, to the west by the Atlantic Ocean, to the south by the Mediterranean Se and widely introduced elsewhere. The largest species is Red alder (A. rubra), known to 40 m tall 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.
Alders establish symbioses with the nitrogen-fixing Actinobacteria Frankiella alni. This bacteria converts atmospheric nitrogen into soil-soluable nitrates which can be utilised by the alder, and favorably enhances the soil fertility generally.
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