The Alder is a very widely diffused tree, growing abundantly by the sides of rivers and streams and in swampy places unfit for the growth of other trees, throughout the whole of Europe, a great part of Asia, the north of Africa and some parts of North America. It is the common or black alder that grows freely in Britain and there are probably few rivers in England which do not have it growing somewhere or other on its banks. Where they most flourish is in moist loam, upon which rains or floods have washed down good layers of humus from woods at a higher elevation. If its roots are well fed and its head is in a humid atmosphere it will grow to a height of thirty to forty feet and occasionally up to one hundred feet.

In its young state, it is a bushy shrub heavily clothed in deep green leaves which as well as young shoots are covered in a sticky substance. The bark of the Alder is rough and black, and the wood is soft. Whilst alive its wood is white, but when cut and exposed to air it becomes red; finally on drying it changes to a pinkish tint. This red colour when cut has linked this tree to "Fear Dearg" the Celtic "red man" who helps humans lost in the Otherworld to escape back to this reality. It produces two kinds of flowers; barren long drooping catkins which appear in autumn and hang on the tree all winter; and fertile oval ones like miniature Fir-cones which are produced in spring. When these ripen, the thick scales of which they are composed separate and allow the seeds to fall, but remain attached to the tree themselves all winter. The seeds are transported by water and to a lesser extent by wind. Woodland dominated by Alder is called "carr".

Alder is a fairy tree and because it grows by the banks of rivers, it is often seen as providing access to the Otherworld. It produces three dyes: brown from its twigs, red from its bark and green from its flowers symbolising Earth, Fire and Water respectively. When the brown dye is combined with iron it also produces a very good black. Spiritually it is linked to steadfastness and the ability to be firmly grounded in ones work.