Common Alder Alnus glutinosa
The Common Alder is native to Britain, Europe, western Asia and north Africa. It grows naturally in damp areas such as river banks and beside lakes but it is now planted in many urban areas. Like all Alders it can add nitrogen to the soil and so is frequently used on reclamation sites. The tree can be confused with two other Alders, the Grey Alder and the Italian Alder, both of which are planted in urban areas. All three have catkins but the Common Alder is easily recognised by its leaf.
Alders have male and female flowers on the same tree. The flowers have no petals, they take the form of catkins. Male catkins are formed in spring, grow upright through the summer and then hang down through the winter until they shed pollen in February/March. Female flowers are pollinated in February/March, grow into round green cone-like catkins in the summer and turn brown and shed seeds in autumn and winter. Female catkins stay on the tree through the winter and the following summer.
A group of Common Alders by a lake, in August.
This is the typical leaf shape, round with a notch at the end.
Female catkins stay on the tree throughout the year. This photograph was taken in July. The catkins look like conifer cones. They are smaller than those of the Italian Alder and larger than those of the Grey Alder. These catkins are open and will have released seeds during the previous autumn and winter.
New male catkins in October. They will release pollen in the following February.
Male catkins stay on the tree after they have shed their pollen in February. This photograph was taken in June. They then drop off as new ones grow.
The bark of young and old trees is cracked into square plates. This is different from the smooth bark of the Italian and Grey Alders.