Natural History

Black Walnut

Juglans nigra, Walnut family (Juglandaceae)

Leaves:
Leaves are pinnately compound. Leaves have a feathery appearance, look more delicate than White Ash leaves. 14-24 leaflets on each leaf, usually an even number of leaflets. Largest leaflets are located in the center of the leaf. End leaflet is usually absent.  Leaflets are lance-shaped, finely saw-toothed, long pointed

Bark:
Bark is dark grayish-brown to blackish, deeply furrowed.  Bark is similar to White Ash, but Black Walnut leaves are thinner and more delicate-looking than White Ash leaves. 

Flowers:
Male and female flowers, clustered in separate catkins, but in same tree (monoecious).

Fruit:
Fruit ripens in autumn. Nut is very hard, covered by thick green husk.  Husk produces a dark-staining, strong-smelling juice. Nuts are edible. Before eating or storage, nuts should be cured in a dry place for at least two weeks. Green husk of fruit has been used to make a blackish dye since colonial times.

Chemistry:
Black Walnut is famous for producing juglone, a chemical released through its roots that is toxic (allelopathic) to some nearby competitor plants.  Juglone causes wilting or yellowing of foliage of neighboring plants. 

Habitat:
Moist well-drained soils, along streams and in mixed hardwoods. Requires lots of light. Not shade-tolerant.

Black Walnut bark is dark and
deeply furrowed. (photo source #5)