The common alder is a deciduous tree that can reach 25 metres in height. Its short-stalked, rounded leaves are toothed around the edges and deep glossy green. The buds and young leaves are slightly sticky. The female flowers are reddish purple and develop into hard cones that contain the seeds. The male catkins are 5 to 10 centimetres long and reddish in colour. The common alder is relatively short-lived, the maximum age typically being 150 years. After the original trunk dies, new shoots can sprout from the base, forming a multi-stemmed clump of new growth.
The common alder is found in cooler regions, forming dense stands around wetlands and along streams and rivers. It is distributed throughout Europe to the Caucasus and Siberia.