Common Alder

• Name also

  Black alder, European alder

• Growing form and height

  Tree with one or several trunks. 5–20 m (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. Wind-pollinated.

• Leaves

  Broadly obovate, with blunt or notched apex. Margins serrate to shallowly incised, rarely deeply incised, vein pairs 5–7. Dark green, glossy, glabrous or sparsely pubescent.

• Buds

  Egg-shaped, glabrous, quite large, dark purple-red, stalked. Scales few, rather large.

• 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. Flowers before coming into leaf.

The genus Alnus comprises approx. 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 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, common alder well tolerates saltiness of seashores. It hybridizes quite commonly with grey alder, in North-Finland hybrids are more common than common alders.

Soft timber of 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.