核桃种

利用

胡桃是重要的木本经济作物，其果仁营养价值丰富，含有多种微量元素和优质蛋白，是全球食用最多的坚果之一。经常食用胡桃可能改善与脑部有关的疾病和心血管疾病。胡桃油富含不饱和脂肪酸，研究表明有抗氧化和抗炎功效，也具有预防记忆障碍的作用。

Juglans regia, known by various common names including the common walnut, English walnut, or Persian walnut amongst other names, is a species of walnut. It is native to Eurasia in at least southwest and central Asia and southeast Europe, but its exact natural area is obscure due to its long history of cultivation.

The species has numerous cultivars which produce the edible walnut consumed around the world and produced predominantly in China. It is widely cultivated across temperate regions throughout the world including those of Eurasia, Australia, and the Americas.

Etymology

The genus name, Juglans, is derived from two Latin words, jovis, which means Jupiter, the chief god of the ancient Roman religion; and glans meaning an acorn or nut. The specific epithet, regia, is defined as royal in references the quality of the fruit and edible nuts.

Description

Juglans regia is a large deciduous tree, attaining heights of 10–25 metres (35–80 feet), and a trunk up to 2 m (6+1⁄2 ft) in diameter, commonly with a short trunk and broad crown. The tallest accurately measured specimen is in the Lagodekhi Protected Areas of the country of Georgia, 29 m (95 ft) tall, and the stoutest in Spain, 9 m (30 ft) in girth. Heights of 34 m in the wild in Kyrgyzstan and 32 m in cultivation in Britain have been reported, but not verified.

Distribution and habitat

Original habitat

One of the centres of origin and diversity of J. regia is Iran, and another further northeast in Central Asia. In Central Asia, genetic diversity is very patchy, with the highest diversity found around Sariosiyo in Uzbekistan, and conspicuously lower in the Arslanbob forests in Kyrgyzstan (these now thought to be of cultivated origin). Another native glacial refugium population with high genetic diversity is found on the southern fringes of the Alps in northeast Italy.

Genetic diversity

J. regia is highly diverse genetically, and has been extensively cultivated for possibly as long as 2,000 years in parts of west Asia and southern Europe.

Its closest relative is Juglans sigillata from western China and the far northeast of India; it differs chiefly in leaves with 9–11 leaflets, and nuts with a much thicker, harder shell.

Ecology

It tends to grow taller and narrower in dense forest competition. It is a light-demanding species, requiring full sun to grow well.

Juglans regia is infested by Rhagoletis juglandis, commonly known as the walnut husk fly, which lays its eggs in the husks of walnut fruit.

Other plants often will not grow under walnut trees because the fallen leaves and husks contain juglone, a chemical which acts as a natural herbicide. Horses that eat walnut leaves may develop laminitis, a hoof ailment.

Cultivation

Walnut trees grow best in rich, deep soil with full sun and long summers, such as the California central valley. Juglans hindsii and J. hindsii × J. regia are often used as grafting stock for J. regia. Mature trees may reach 15 m (50 ft) in height and width, and live more than 200 years, developing massive trunks more than 2.4 m (8 ft) thick.

Pests

Particular cultivars of J. regia may be more infested by R. juglandis than others because of varying walnut husk softness or thickness.

Toxicity

Allergy

Walnuts and other tree nuts are food allergen sources having potential to cause life-threatening, IgE-mediated allergic reactions in some individuals.

Uses

Nutrition

Walnut kernels are 4% water, 65% fat, 15% protein, and 14% carbohydrates. In a reference amount of 100 g (3.5 oz) providing 654 calories, the kernels supply several micronutrients in rich amounts (20% or more of the Daily Value, DV), including the dietary minerals manganese, phosphorus, magnesium, zinc, and copper, among others; B vitamins B6, thiamine, and folate; and dietary fibre.

The fatty acid composition includes 6% saturated fats, 10% monounsaturated fats, and 49% polyunsaturated fats (USDA source).

In culture

In Skopelos, a Greek island in the Aegean Sea, local legend suggests whoever plants a walnut tree will die as soon as the tree can "see" the sea. Most planting is done by field rats (subfamily Murinae). In Flanders, a folk saying states: "By the time the tree is big, the planter surely will be dead." (Dutch: Boompje groot, plantertje dood). These sayings refer to the relatively slow growth rate and late fruiting of the tree.