Walnut
Edible seed of Juglans trees, used in cuisine and traditional medicine.
A walnut is the edible seed of any tree of the genus Juglans (family Juglandaceae), particularly the Persian or English walnut, Juglans regia. Walnuts are accessory fruit, as the outer covering is technically an involucre and not morphologically part of the carpel, making them drupe-like nuts rather than true drupes. After full ripening, the shell is discarded and the kernel eaten; nuts of the eastern black walnut (Juglans nigra) and butternuts (Juglans cinerea) are less commonly consumed.
- species
- Juglans regia (Persian/English walnut), Juglans nigra (black walnut), Juglans ailantifolia (Japanese walnut/heartnut)
- origin
- Persian walnut originates from Iran; black walnut native to eastern North America
- field
- Botany, agriculture, nutrition
- known_for
- Edible seed, culinary uses, health claims, and historical name 'royal nut'
- production_2023
- 4 million tonnes worldwide; China 35%, followed by US, Iran, Turkey
Lore & Background
Walnuts have been known since ancient times, referred to as 'royal nut' during the Ottoman and Byzantine eras. An article on walnut tree cultivation in the Iberian Peninsula appears in Ibn al-'Awwam's 12th-century Book on Agriculture. The 'wal' element in the name is Germanic, meaning foreign, especially Latin or non-Germanic, as seen in German Walnuss, Dutch walnoot, and Swedish valnöt.
Reader's Guide
Walnuts are significant as a widely cultivated nut crop, with world production reaching 4 million tonnes in 2023, led by China, the United States, Iran, and Turkey. They are valued for their nutritional profile—rich in polyunsaturated fatty acids, protein, and dietary minerals such as manganese—and for a qualified health claim from the US FDA that daily consumption of 1.5 ounces may reduce the risk of coronary heart disease when part of a low saturated fat and low cholesterol diet. However, the European Food Safety Authority found a cause-and-effect relationship did not exist between walnut consumption and reduction of blood LDL-cholesterol levels, though it authorized a health claim regarding improvement of endothelium-dependent vasodilation. Walnuts also pose allergy risks, with lifetime prevalence about 0.4% in Europe and the US, and potential cross-reactivity with pecans, cashews, and other tree nuts. Proper storage is critical to prevent aflatoxin-producing mold, with ideal temperatures of −3 to 0 °C and low humidity.
Did You Know?
- Walnuts are accessory fruit, not true drupes, because the outer covering is an involucre.
- The walnut shell is usually in two segments, but three- or four-segment shells can also form.
- Walnut hulls contain juglone at concentrations of 2–4% fresh weight, which can stain hands and cause skin irritation.
- The 'wal' in walnut is Germanic for 'foreign,' as seen in words like Wales and Wallachia.
Frequently Asked Questions
What is a walnut?
A walnut is the edible seed produced by trees in the genus Juglans (family Juglandaceae), with the most widely consumed type being the Persian or English walnut (Juglans regia). The kernel inside is what people eat after the hard shell is removed.
Is a walnut botanically a true nut?
No — it is classified as an accessory fruit. The outer husk is technically an involucre rather than a true part of the carpel, which makes walnuts drupe-like structures instead of genuine true nuts.
Where do walnuts originally come from?
The Persian walnut (Juglans regia) is native to Iran, while the black walnut (Juglans nigra) is indigenous to eastern North America. A Japanese variety, Juglans ailantifolia, also exists but is less commonly eaten.
How much walnut is grown worldwide?
Global production reached roughly 4 million tonnes in 2023. China leads with about 35% of output, followed by the United States, Iran, and Turkey.
Why is the Persian walnut sometimes called the 'royal nut'?
The name 'regia' in its scientific name Juglans regia translates to 'royal,' a nod to its long history as a prized and widely cultivated edible seed in cuisine and traditional medicine across Persia and beyond.
More in Plants & Crops 1-17
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record