Images: ©Jouko Lehmuskallio
Common Alder
Alnus glutinosa
- Family: Birch Family – Betulaceae
- Growing form and height: Tree with one or several trunks. 5–20 m (ca. 15–65 ft.).
- Flower: Small male and female flowers in separate inflorescences. Male flower with four yellowish-green to yellow perianth-segments. Male inflorescence a dense, pendent catkin. Female flower lacking perianth, red to reddish-brown. Female inflorescence a cylindrical and hard, long-stalked catkin.
- Leaves: Broadly obovate, with blunt or notched apex. Margins serrate to shallowly incised, rarely deeply incised. Dark green, glossy, glabrous or sparsely pubescent.
- Fruit: Female catkin ripening into a hard, brown cone-like structure. Fruit a very small nut.
- Habitat: Sea and lake shores, streamside swamps, edges of nutrient-rich mires, spruce-broadleaf swamps, moist broadleaf woods. Also a park and forestry tree.
- Flowering time: April.
The genus Alnus comprises appr. 30 species of trees or large shrubs which flower before coming into leaf in the spring. They have root nodules which contain nitrogen-fixing bacteria. Thus they improve the soil quality. The genus is best represented in North America and East Asia.
Originally the common alder was a tree of nutrient-rich wetlands and other waterlogged soils. It thrives only on sites with flowing surface or ground water. Its seeds are also dispersed by water. In addition, the common alder well tolerates the saltiness of seashores.
The soft timber of the common alder was formerly used for making wooden shoes and moulds in glass factories. It is also suitable for constructions in or near water as it is decay-resistant.
