black locust
Robinia pseudoacacia L.

Overview

Appearance

Robinia pseudoacacia is a deciduous tree that, while native to parts of the United States, has spread to and become invasive in other parts of the country. Trees grow from 40-100 ft. (12-30 m) in height. Trees grow upright in forests, but develop an open growth form in more open areas. The bark of black locust is light brown, rough, and becomes very furrowed with age.

Foliage

Leaves are pinnately compound with 7-21 small, round leaflets per leaf. Leaflets are 1.5 in. (4 cm) long. A pair of long, stipular spines is found at the base of most leaves.

Flowers

Flowering occurs in the spring, when showy, fragrant, white to yellow flowers develop in 8 in. (20.3 cm) long clusters.

Fruit

The flowers give way to a smooth, thin seed pod that is 2-4 in. (5.1-10.2 cm) in length.

Ecological Threat

Robinia pseudoacacia is native to the Southern Appalachians, the Ozarks, and other portions of the Midsouth, but is considered an invasive species in the prairie and savanna regions of the Midwest where it can dominate and shade those open habitats.

Resources

• Fire Effects Information System - USDA Forest Service
• Silvics of North America - USDA Forest Service
• Element Stewardship Abstract - The Nature Conservancy
• Weeds Gone Wild: Alien Plant Invaders of Natural Areas - Plant Conservation Alliance

Selected Images

Maps

Invasive Listing Sources

• California Invasive Plant Council
• City of Ann Arbor Michigan Parks and Recreation
• Connecticut Invasive Plant List
• Connecticut Invasive Plant Working Group
• 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.
• Invasive Plant Association of Wisconsin
• Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
• John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995.
• Maine Noxious Weeds
• Massachusetts Invasive Plants Advisory Group List
• Massachusetts Noxious Weeds
• Massachusetts Prohibited Plant List
• Minnesota Noxious Weeds
• National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
• Native Plant Society of Oregon, 2008
• New Jersey Invasive Species Strike Team 2017 Invasive Species List
• New York Regulated and Prohibited Invasive Species - Regulated
• Ontario’s Invading Species Awareness Program Tracked Species List
• Reichard, Sarah. 1994.  Assessing the potential of invasiveness in woody plants introduced in North America. University of Washington Ph.D. dissertation.
• Rhode Island Natural History Survey
• WeedUS - Database of Plants Invading Natural Areas in the United States
• Wisconsin Noxious Weeds
• Wisconsin's Invasive species rule – NR 40

References