AppearanceAlnus glutinosa is a tree in the birch family that can grow up to 50 ft (15.24 m) tall with the crown spreading from 20-40 ft (6.1-12.2 m) wide. It can be single or multi-stemmed, with a smooth greyish-green bark that turns a speckled grayish-brown. It is native across Europe, temperate Asia, and north Africa. It has been planted extensively in North America as an ornamental tree and for erosion control.Foliage The leaves are simple, alternate and doubly-toothed.Flowers The individual flowers are small and inconspicuous individually, but together they form a catkin. They flower in the spring and catkins remain on the trees through the fall. Fruit Fruits are obovate samaras. The wings are reduced to narrow thinkened ridges. Ecological ThreatA. glutinosa can grow on a wide range of soils has been seen to form monotypic stands. Although it can toleate droughts, it prefers moist, damp conditions, especially near water sources. It commonly grows in riparian zones, wetlands, along ponds and lakes. It also grows in forests, forest wetlands and in urban areas.