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 glutinosa is a popular tree of moist to wet soils. Commonly known as Black Alder it is a moderate to fast-growing deciduous tree that usually grows to 12m to 15m in height with a 6m to 12m spread and a 30cm to 45cm trunk but is capable of reaching 24m in height in the woods. Pyramidal when young, Black Alder often has multiple stems, making it ideal for use as a screen or bonsai specimen, the trees eventually becoming more rounded or oval as they mature. The two- to four-inch-wide, dark green, roundish leaves with toothed edges and pale undersides are joined in spring by rather insignificant male and female flowers. Foliage remains green well into autumn. It is the fruits that are most interesting—small, nutlike, 2.5cm “cones” that persist throughout autumn and winter, long after the darkening leaves have fallen. These fruits, along with the attractive, dark brown, furrowed bark and multi-stemmed growth habit, make Black Alder an attractive landscape specimen throughout the winter. The fruits are food for a variety of wildlife.