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 cordata is a handsome, fast-growing large tree, sometimes seen gardens. It also makes a beautiful bonsai specimen. The Italian Alder is often regarded as the finest of the species. Native to southern Italy, the Italian Alder has an attractive conical shape, providing good winter interest, and glossy leaves. Its tolerance of both a wide range of soils and of urban pollution makes it a useful tree for the reclamation of derelict sites as well as a specimen tree for parks and woodland. Tolerant of a wide range of soils, including chalk, the Italian Alder also does well on compacted urban sites and derelict land. It copes well with pollution in towns, and its resistance to wind makes it useful for screening and hedges.