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Trees of Iowa: An Interactive Key

Black Locust
(Robinia pseudoacacia)



Leaves are alternate, compound, with thorns or spines.
Black Locust FlowerBlack Locust Bark

Not native to Iowa, the black locust is included here because it has been planted so widely over the state, has escaped from cultivation and is sometimes found growing in mixture with native species.  Its natural range extends from Pennsylvania southwest ward to Alabama and west ward to southern Illinois.  It has been planted widely in Iowa for post production and erosion control.  The tree often suffers extensive damage from the locust borer insect.

Hardiness: zones 4 through 8

Growth Rate:
Aggressive; Rapid

Mature Shape:
Upright to spreading ovular shap

Height:
50 feet

Width:
25 feet

Site Requirements:
Prefes rich, deep, moist, well-drained, and full to partial sun. However, commonly found in poor soil conditions, especially thin and near limestone outcrops.

Flowering Dates: May - June

Seed Dispersal Dates: September - April

Seed Bearing Age: 10 years

Seed Bearing Frequency: Yearly or bi-yearly

Seed Stratification: Soak seeds in warm water for 24 hours.
Black Locust TwigBlack Locust Leaves

The leaves are pinnately compound with 11 to 15 leaflets 1 to1-1/2 inches long, rounded at both ends and with smooth margins.

Black Locust FlowersBlack Locust Fruit

The twigs are crooked and angular with short, stout, single, unbranched thorns, one-half inch long. The fruit is a dark, red-brown, flexible pod 3 to 4 inches long, containing small, reddish brown beanlike seeds. On young branches the bark is smooth and greenish to brown incolor. On older branches and trunks it is broken into a network of coarse, deep ridges and is gray to gray-brown in color.

 

Click on a thumbnail image below to view a larger picture.
Black Locust Flowers Black Locust Twigs Black Locust Fruit Black Locust Leaves Black Locust Flowers Black Locust Fruit Black Locust Leaves Black Locust Flowers Black Locust Fruit Black Locust Leaves Black Locust Flowers Black Locust Bark Black Locust Flowers Black Locust Fruit Black Locust Leaves Black Locust Bark Black Locust Thorns Black Locust Thorns Black Locust Thorns