alnus

Alnus is a genus of flowering plants in the family Betulaceae, commonly known as alders. The genus includes several dozen species of deciduous trees and shrubs native to temperate regions of the Northern Hemisphere, with a concentration along wetlands, riverbanks, and damp forests.

Leaves are simple, alternately arranged, typically ovate with serrated margins. In spring, alders produce catkins, and the flowers are wind-pertilized. The fruit are woody, cone-like structures that release small, winged seeds.

Ecology: Alnus species form actinorhizal symbioses with the nitrogen-fixing bacterium Frankia in root nodules, allowing them to enrich nitrogen-poor soils. They are often early-successional, colonizing disturbed or waterlogged sites and stabilizing shorelines.

Taxonomy and distribution: The genus includes species such as Alnus glutinosa (European alder), Alnus rubra (red alder) of western North America, and Alnus incana (gray alder).

Uses: Alder wood is light and easy to work, used for timber, veneer, and crafts; the bark contains tannins used in leather tanning. Alders are planted for habitat restoration, soil stabilization, shaded wetlands, and ornamental purposes due to rapid growth and tolerance of wet soils.