Black alder, aliso

Description:

Alnus glutinosa is a tree that thrives in moist soils, and grows under favourable circumstances to a height of 20–30 m. Alder is a deciduous tree belonging to the birch family of the genus Alnus, which includes approximately 30 species of trees and shrubs. It is characterized by its 5–10 cm short-stalked rounded leaves 6–12 cm long, becoming wedge-shaped at the base and with a slightly toothed margin. When young they are somewhat glutinous, whence the specific name, becoming later a glossy dark green. As with some other plants, growing near water it keeps its leaves longer than do trees in drier situations. The glossy green foliage lasts after other trees have put on the red or brown of autumn, which renders it valuable for landscape effect. As the Latin name glutinosa implies, the buds and young leaves are slightly sticky with a resinous gum. Alnus glutinosa is most noted for the symbiotic relationship with the bacterium Frankia alni, which forms nodules on the tree's roots. This nitrogen-fixing bacterium absorbs nitrogen from the environment and fixes it into a form available to the tree. In return, the bacterium receives carbon which is produced by the tree through photosynthesis. This relationship, which improves the fertility of the soil environment, has established A. glutinosa as an important pioneer species in ecological succession. A. glutinosa is also a host to a wide variety of moss and lichen. Some common species found on A. glutinosa include: Tree Lungwort (Lobaria pulmonaria), Stenocybe pullatula, and Menneguzzia terebrata.

Habitat:

Mediterranean forest