Leaf:  Alternate, pinnately compound with 7 to 21 leaflets; leaflets oval, short pointed at tip, rounded at the base, 2 cm to 5 cm long and 1.3 cm to 2 cm wide; smooth without jagged teeth; blue green, smooth on upper surface; pale and smooth on the lower surface except for the veins; leafstalks slender, up to 45 cm long, green, smooth; turning yellow in Autumn.

Flower:  Long drooping clusters in showy racemes, up to 25 cm long; appearing in May and June after the leaves; each flower perfect, growing in leaf axil; white with a yellow spot, fragrant.

Fruit:  Legumes up to 4 inches long and about 1/2 inch wide; flat, smooth, reddish-brown, with 4-8 seeds; opens on the tree disbursing seeds from September to April.

Twig:  Slender but not long, regular, often zigzag, reddish-brown, with a pair of short, sharp thorns where each leaf is attached; leaf scars alternate, 3-lobed, with 3 bundle traces per lobe; buds sunken in the twig, dark brown, without bud scales, up to 3mm long.

Bark:  Grey or black, deeply furrowed with numerous elevated, scaly ridges, bark on younger trees greenish, smooth, with numerous scaly ridges beginning to develop.

Form:  Medium tree up to 21 m tall; trunk diameter up to 0.7 meters; crown narrowly oblong, with irregular ascending  or spreading branches. 
 

Discussion

The black locust's scientific name is Robinia pseudoacacia.  Its genus name derives from a French herbalist in the 16th century.  His name was Jean Robin; he was a gardener to Henry IV and Louis XIII.  The species name means false acacia.  

Black locust is important in the ecosystem for food and shelter.  Older trunks have hollows used as nesting cavities by downy woodpeckers, hairy woodpeckers, and flickers.  Deer eat the leaves, and bobwhite, other game birds, and squirrels eat the seeds.  The flowers are fed upon and pollinated by insects, primarily bees.  Black locust improves the soil because nodules on its roots house nitrogen-fixing bacteria.

Black locust is a common tree in disturbed areas.  Once started, the tree grows quickly, giving it a head start.  Even when the trees are removed, their seeds stay in the ground and remain viable for many years.  Once the area is disturbed again, the seeds break dormancy and black locust reappears.  

Black locust wood is strong, hard, and heavy.  The wood has had many uses in the past, being made into fence posts, tool handles, police clubs, railroad ties, boxes, crates, tree nails for wooden ships, mine timbers, poles, insulator pins, pegs, and novelties.  Black locust was also used as pulp and firewood.  

Because of its usefulness and habit of getting a fast start, black locust was planted across the country.  It has since escaped from confines and has become naturalized.  Black locust was first planted Europe circa 1601 by either Jean Robin or his son Vespasien, probably after they received seeds from the New World, and it subsequently became distributed across Europe.  Today black locust is planted in many parts of the world to be used for firewood, poles, fences, and construction.

In the United States, black locust is used to control erosion on disturbed sites.  It acts as a "nurse species", adding nitrogen to the soil and providing a degree of shelter for other plants to begin growing.  This species has been used in strip mine reclamation because it tolerates a fairly wide range of soil pH.  

Black locust is not often planted in landscapes partly because the arrangement of its branches makes it susceptible to wind damage.   The tree makes large roots near the surface, sometimes buckling sidewalks or interfering with mowing.  

Black locust may have considerable economic and environmental impact in the future, as it is suitable for planting as a biomass fuel, a source of renewable energy. 

Distinguishing Characteristics

Black locust is identified by its paired thorns and up to 21 oval, smooth-edged leaflets making up the pinnately-compound leaves.  Black locust has nodules on the roots to harbor nitrogen-fixing bacteria; honey locust lacks these nodules.

Distribution

Native to the southern Appalachians and the Ozarks, but now naturalized throughout North America, occupying disturbed sites, streamsides, rich bottomlands, woodlands, thickets, and road sides.

Images

Click each small picture to see a larger image. 

October, 2003  JW	October, 2003  JW	October, 2003  GW
October, 2003  GW	October, 2003  JW	October, 2003  GW

Location

N 39.27929°   W -89.89030°                    
In the vacant lot east of McDonald's, towards the back where the gravel ends, West Main Street, Carlinville, Macoupin County, IL.

Copyright

Photos © 2003 Gary Wilson and Jerod Weller, Carlinville High School, linke@carlinvilleschools.net       
           

References

Mohlenbrock, Robert H.  1996.  Forest trees of Illinois.  8th ed.  Illinois Dept. of Conservation Publications, Springfield.  331 pp.

J.C. Huntley.  Northeastern Area, USDA Forest Service  (accessed 12/03)
http://www.na.fs.fed.us/spfo/pubs/silvics_manual/volume_2/robinia/pseudoacacia.htm

Athenic Systems (accessed 12/03)
http://www.treeguide.com/family.asp?familyID=120&Redion=World

Jo-Ann Kaiser (accessed 12/03)
http://www.iswonline.com/wwp/wom/blacklocust.shtml

West Virginia University (accessed 12/03)
http://www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm

Wisconsin Department of Natural Resources (accessed 12/03)
http://www.dnr.state.wi.us/org/land/er/invasive/factsheets/locust.htm

Botanical Word Meanings and Name Deviations (accessed 12/30)
http://www.calflora.net/botanicalnames/pageQ-S.html

Forest World (accessed 12/03)
http://www.forestworld.com/public/silvics/silvics_frame.html

Ohio Division of Forestry, Ohio Department of Natural Resources
http://www.hcs.ohio-state.edu/ODNR/Education/ohiotrees/locustblack.htm

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