Walnuts (genus Juglans) are plants in the family Juglandaceae. They are deciduous trees, 10–40 meters tall, with pinnate leaves 200–900 millimetres long, with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts but not the hickories in the same family. The 21 species in the genus range across the north temperate Old World from southeast Europe east to Japan, and more widely in the New World from southeast Canada west to California and south to Argentina. The Latin name, Juglans, derives from Jovis glans, "Jupiter's acorn": figuratively, a nut fit for a god.
Walnuts are very attractive trees in parks and large gardens. Walnut trees are easily propagated from the nuts. Seedlings grow rapidly on good soils. The Japanese Walnut in particular is grown for its huge leaves, which have a 'tropical' appearance.
The best-known member of the genus is the common walnut (J. regia, literally "royal walnut"). The two most commercially important species are J. regia for timber and nuts, and J. nigra for timber. Both species have similar cultivation requirements and are widely grown in temperate zones.
The nuts of all the species are edible, but the walnuts commonly available in shops are from the common walnut, the only species which has a large nut and thin shell. A horticultural form selected for thin nut shells and hardiness in temperate zones is sometimes known as the 'Carpathian' walnut. The nuts are rich in oil, and are widely eaten both fresh and in cookery.
The walnut shell has a wide variety of uses. It is commonly used as an organic abrasive, to polish and clean a number of different materials. Eastern black walnut shell is the hardest of the walnut shells, and therefore has the highest resistance to break-down. It is environmentally friendly and can be recycled.
