The distribution area of the walnut is central, western, and southern Europe, and it is also cultivated in Asia Minor, North Africa, Northern India, and China. Its altitudinal distribution in Central Europe is up to 850 m/asl, and in southern Italy, it grows even up to 1800 m/asl. Walnut trees can be over 100 years old.
Walnut trees generally reach a height of about 25 m. The length of the trunk is up to 8 m, and the diameter is usually up to 1 m, rarely larger. The crown of the walnut tree is very wide, oval, with many thick branches. The bark of the trunk is smooth, light gray when young, and later cracks longitudinally.
The Walnut is a deciduous type of tree. The sapwood is grey-white and narrow, and the heartwood is dark-brown to black-brown, mostly with dark stripes. Raw wood smells like leather. The growth rings are striking, relatively wide, and concentric, and the tracheas are diffusely-porous and large, visible. The strips of wood are thin and low, homo and heterocellular, and difficult to see. Axial parenchyma is unilateral and zonally diffuse.