Genus Juglans Rank Species | ||
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Similar Walnut Tree, Butternut, Juglans mandshurica, Pterocarya, Juglandaceae | ||
Juglans ailantifolia (synonyms J. cordiformis and J. sieboldiana and J. mandshurica var. sachalinensis), the Japanese walnut (Japanese: 鬼胡桃 oni-gurumi), is a species of walnut native to Japan and Sakhalin. It is a deciduous tree growing to 20 m tall, rarely 30 m, and 40–80 cm stem diameter, with light grey bark. The leaves are pinnate, 50–90 cm long, with 11-17 leaflets, each leaflet 7–16 cm long and 3–5 cm broad. The whole leaf is downy-pubescent, and a somewhat brighter, yellower green than many other tree leaves. The male flowers are inconspicuous yellow-green catkins produced in spring at the same time as the new leaves appear. The female flowers have pink/ red pistils. The fruit is a nut, produced in bunches of 4-10 together; the nut is spherical, 3–5 cm long and broad, surrounded by a green husk before maturity in mid autumn.
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Uses
The edible nuts have an oily texture. The husks are also used to make a yellowish dye.
The very bold, decorative leaves and the attractive catkins produced in spring make it an excellent ornamental tree for planting in parks and large gardens.
Unlike the closely related and very similar North American butternut, Japanese walnut is resistant to the canker disease caused by the fungus Sirococcus clavigignenti-juglandacearum. This has led to its being planted as a replacement for butternuts in North America. The two species hybridise readily; the resulting hybrid Juglans x bixbyi (otherwise known as J. cinerea x ailantifolia or 'buartnut') is also resistant to canker and is likewise planted as a replacement for butternuts. Japanese walnut is distinguished from butternut by its larger leaves and round (not oval) nuts. Prospect Rock Permaculture in Vermont has been backcrossing buartnuts with native butternuts, resulting in 'butterbuarts', which will most likely bear greater resemblance to the butternut parentage, although may also be more susceptible to the canker.
The wood is light and takes polish well, but is of much lower quality than Persian walnut wood. It is often used to make furniture.
Cultivars
The heartnut is a specific variety of the Japanese walnut, notable for its distinctively heart-shaped cross-sectional appearance of the fruit. This cultivar is characterized by shells that are more easily cracked, often resulting in whole, unbroken nutmeats upon opening. Unlike its relatives, the black and Persian walnuts, the heartnut offers a sweeter taste devoid of the typical bitter aftertaste.
Diseases
The only significant disease Japanese walnuts are susceptible to is the Walnut Bunch Disease.