alder (redirected from alder trees)

alder (ôl`dər), name for deciduous trees and shrubs of the genus Alnus of the family Betulaceae (birch family), widely distributed, especially in mountainous and moist areas of the north temperate zone and in the Andes. The black alder (A. glutinosa) is an Old World species now naturalized in E North America. Its bark, still used for dyes and tanning, was formerly considered medicinal; its wood is useful chiefly as charcoal. A. rugosa, the speckled alder, forms extensive swamp thickets in Eurasia and North America. The red alder (A. rubra), the largest tree of the genus, is the most important hardwood timber tree in its native region, the Pacific coast of North America. Alder trees are classified in the division Magnoliophyta, class Magnoliopsida, order Fagales, family Betulaceae.

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alder

Alder (Alnus glutinosa)

(credit: Earl L. Kubis—Root Resources)

Any of about 30 species of ornamental shrubs and trees in the genus Alnus, of the birch family, found throughout the Northern Hemisphere and western South America on cool, wet sites. Alders are distinguished from birches by their usually stalked winter buds and by cones that remain on the branches after the small, winged nutlets are released. Alders have scaly bark, oval leaves that fall without changing colour, and separate male and female flowers (catkins) borne on the same tree. Some familiar North American alders are the red alder (A. rubra or A. oregona); the white, or Sierra, alder (A. rhombifolia); and the speckled alder (A. rugosa). Alder wood is fine-textured and durable, even under water; it is useful for furniture, cabinetry, and lathe work and in charcoal manufacture and millwork. Alders' spreading root systems and tolerance of moist soils lend them to planting on stream banks for flood and erosion control.