The Alnus genus commonly known as Alder belongs to the birch family Betulaceae. The genus comprises about 30 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 and the northern Andes. The catkins of some alder species have a degree of edibility, and may be rich in protein. Reported to have a bitter and unpleasant taste, they are more useful for survival purposes. The wood of certain alder species is often used to smoke various food items, especially salmon and other seafood.

Alnus rhombifolia, the white alder, is an alder tree native to western North America. Alnus rhombifolia is a medium-sized deciduous tree growing to 15–25 metres (rarely to 35 metres) tall, with pale grey bark. The flowers are produced in catkins. The white alder is closely related to the red alder (Alnus rubra), differing in the leaf margins being flat, not curled under. Like other alders, it is able to fix nitrogen, and tolerates infertile soils. Some Plateau Indian tribes use white alder medicinally for female health treatment needs.