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.
Alder (Alnus glutinosa)—Earl L. Kubis/Root Resources
This entry comes from Encyclopædia Britannica Concise.
For the full entry on alder, visit Britannica.com.
Seen & Heard
What made you look up alder? Please tell us what you were reading, watching or discussing that led you here.