Appearance

Alnus 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 Threat

A. 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.

Resources

• Weed of the Week - USDA Forest Service

Selected Images

Maps

Invasive Listing Sources

• City of Ann Arbor Michigan Parks and Recreation
• Hoffman, R. & K. Kearns, Eds. 1997. Wisconsin manual of control recommendations for ecologically invasive plants. Wisconsin Dept. Natural Resources, Bureau of Endangered Resources. Madison, Wisconsin. 102pp.
• Indiana Invasive Species Council - Invasive Plant List
• Indiana Terrestrial Plant Rule
• Invasive Plant Species of West Virginia
• Kentucky Exotic Pest Plant Council - Watch List
• Maine Invasive Plants
• Massachusetts Invasive Plants Advisory Group List
• Massachusetts Noxious Weeds
• Minnesota Noxious Weeds
• National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
• New Hampshire Invasive Species Committee. 2005. Guide to Invasive Upland Plant Species in New Hampshire. New Hampshire Department of Agriculture,  Markets and Food Plant Industry Division and New Hampshire Invasive Species Committee.
• New Hampshire Prohibited Invasive Species
• New Jersey Invasive Species Strike Team 2017 Invasive Species List
• Ontario’s Invading Species Awareness Program Tracked Species List
• Pennsylvania Department of Conservation and Natural Resources Invasive Plants
• Reichard, Sarah. 1994.  Assessing the potential of invasiveness in woody plants introduced in North America. University of Washington Ph.D. dissertation.
• WeedUS - Database of Plants Invading Natural Areas in the United States
• Wisconsin Noxious Weeds
• Wisconsin's Invasive species rule – NR 40

References