Black Locust 

Robinia pseudoacacia L. 

Description 

 Black locust, a member of the pea family (Fabaceae), grows to approximately 60-80 feet¹.  The bark is deeply furrowed and is dark reddish-brown to black in color⁵.  Leaves are alternate on the stem may have a pair of sharp, persistent thorns growing at each node⁵.  The leaves are pinnately compound divided into 9-19 ovate to oblong leaflets, rounded at the ends and with smooth margin³.   The many flowered racemes are produced in late April or early May are fragrant.  Flowers are typically white but may be pink or purple and are insect pollinated.  The fruits are dried legumes with 4-7 seeds that split carrying the seeds.  They are wind dispersed.  

 Black locust leaves and flowers.  @ J. Brighton, 2010, Maryland Plant Atlas² 

Black locust legume fruit.  @ J. Brighton, 2012, Maryland Plant Atlas² 

 Stipule thorns of black locust.  @ S. Matson, 2010.  CalPhotos¹² 

 Distribution 

 In its native range, black locust can be found on the lower slopes of the Appalachian Mountains from Pennsylvania to Alabama, and can also be found in the north along the slopes and forest edges of southern Illinois, Indiana, and Missouri secondary population exists primarily in the Ozark Mountains⁴.  In western Maryland and northern Virginia, black locust are a relatively common species in disturbed forests, occurring with basswood, chestnut oak, flowering dogwood, eastern hophornbeam⁵.  Black locust forms a symbiotic relationship with a nitrogen fixing bacterium¹³.  Black locust trees are adaptive to many different climates, deep well-drained soils, and are commonly sighted in areas that have been disturbed like roadsides, degraded woods, and old fields⁴.   Black locust has escaped cultivation and has naturalized throughout the United States and in parts of Asia and Europe¹³. 

 Native range of black locust.  USDA¹³ 

Wildlife Importance 

 Black locust trees are valuable to wildlife as they provide food and shelter to many wildlife species.  The white flowers of the black locust have a sweet smell and produce abundant amounts of nectar and pollen, making them important for honeybees, native bees as well as other native pollinators like hummingbirds and butterflies⁶.  Many species of songbirds use the tree’s branches to build nests or eat the caterpillars and other insets that feed upon the leaves⁶.  Other species like white-tailed deer, rabbits, and squirrels have all been known to eat black locust foliage or seed pods⁶. 

Economic Importance 

 The black locust is important for its timber as they are often used for fence, hardwood lumber, and as a source of fuel⁶.  The tree is often planted for erosion control and to increase soil fertility via nitrogen fixation⁷.  It is used for reclaiming mine spoils¹³. 

Threats 

Outside of its historic North American range, black locust poses various threats to native vegetation in dry and sand prairies, oak savannas and upland forest edges⁹.  Black locust trees are important in helping stop erosion and serve as primary colonizers after natural disasters.  It can spread from the roots, forming pure stands that out-compete native vegetation¹⁰.  There are two native insects that can cause damage to the Black Locust: the locust borer (Megacyllene robiniae) and the locust leafminer (Odontota dorsalis)⁹.

 Interesting Facts 

• Other names common names for the black locust include: yellow locust, white locust, red locust, green locust, pea flower locust, common locust, and false acacia⁷. 
• Black ocusts can live to be 90 years old⁵. 
• Black locust trees produce hard, durable, rot-resistant wood and are often planted as fence posts¹⁰.
• The black locust is one of the strongest timbers in North America.  This tree was the most favored by the colonial people in Jamestown, both as an ornamental and as a utilitarian tree¹¹. 
• Black locust may have contributed to the American victory over the British in the War of 1812.  In the pivotal battle on Lake Champlain, the American ships were held together with pins of black locust, a very hard, but elastic wood, that enabled cannonballs to have minimal effect.  The British were held together with oak pins that shattered upon the ship being hit by cannon balls.  After the war, the british imported black locust wood for their ships¹¹. 

 References  

1. USDA Plants:  Robinia pseudoacacia
2. Maryland Plant Atlas:  Robinia pseudoacacia
3. Lady Bird Johnson Wildflower Center:  Robinia pseudoacacia
4. Yale Nature Walk:  Robinia pseudoacacia 
5. USDA-Forest Service Fire Effects Information System:  Robinia pseudoacacia 
6. Shannon Trimboli Backyard Ecol.ogy:  Black locust–an impoortant plant for pollinaors and other wildlife
7. North Carolina State Extension:  Robin pseudoacacia
8. The economic implications of Robinia pseudoacacia L. (black locust) on agriculture production in South Africa.  Agricon 58:  216-228.
9. Plant Conservation Alliance Fact Sheet: Black locust
10. Brandeis University: Black locust 
11. Live Science–Black locust: the tree on which the US was built
12.  CalPhotos:  Robina pseudoacacia
13. USDA-Forest Service Silvics, Vol. 2,  Hardwoods:  Robinia pseudoacacia

 

Contributed by K. Ujeta-Estaban and V. Tayviah 

Towson University Glen Arboretum