Walnut, Black (Juglans nigra)

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Black Walnut is native to eastern north America and was introduced to Europe in 1629.

Common name: black walnut

Scientific name: Juglans nigra
Family: Juglandaceae

UK provenance: non-native

Interesting fact:  the roots contain a growth-inhibiting chemical which prevents many other trees and plants growing near it, this is said to affect tomatoes and apples in particular.

What does black walnut look like?

Overview: it is a large tree which can reach 30 or 40 metres in height. The tree gets its name from its dark, heavily ridged bark which occurs even when it is still young.

Leaves: pinnate and larger than that of the common walnut (Juglans regia) with more leaflets. Individual leaflets are oval, pointed, irregularly toothed and hairy underneath.

Flowers: both male and female flowers appear from late May-early June. The male flowers are on 8-10cm long catkins that droop from the branches. Female flowers appear in clusters.

Fruits: in autumn, flowers turn to a brownish-green plum-like fruit. The brown nut is held inside this large semi-fleshy husk which is rougher than that of common walnut. The shells are notoriously hard to break, drying them out makes it easier to crush and open the shells.

Look out for: the leaflets have toothed edges. Crushed leaves have a strong smell.

Could be confused with: common walnut (Juglans regia). Black walnut has a greater number of leaflets (7-9 pairs) with toothed edges. Black walnut leaflets are also generally smaller and narrower than those of common walnut.

Identified in winter by: inside the twig the pith, or spongy tissue, is segmented. Buds have horseshoe shaped leaf scars, or marks, left by fallen leaves, at their base.

Where to find black walnut

In Britain it thrives best in warmer regions towards the south. It prefers fertile, lowland soil and needs plenty of light.

Value to wildlife

Squirrels and some birds feed off the nuts of the tree whilst the flesh is still green and the husk easier to penetrate.

Mythology and symbolism

Black walnut is mentioned in Native American creation myths.

How we use black walnut

Black walnut has been used by native people for thousands of years. Native American ethnobotany has revealed many medicinal uses for the bark, leaves, husks, and nuts of black walnut, including its utility as a mosquito repellent, a dermatological aid, an antidiarrhoeal, a laxative, and an anthelminthic. In one form or another, this species has been used to relieve the symptoms of fever, kidney ailments, gastrointestinal disturbances, ulcers, toothache, syphilis, and snake bite, among others.

Western science has shown that the fruit husks of the black walnut contain juglone – a compound that inhibits bacterial and fungal growth, and may be valuable in controlling dermal, mucosal and oral infections in humans. It is also being tested for its anticancer properties.

Timber from the black walnut is very attractive and very valuable. It is a strong and naturally durable wood, and the heartwood shows desirable mottled effects. It polishes to a high shine and is therefore used by craftsmen around the world for high-end furniture and ornaments.

The nuts can be eaten but they have a bitter taste if picked when the casing has hardened. It is better to extract the nut from the tree whilst the husk is still green and then dry the nut, to ensure it is not rubbery, before eating.

The seeds also give out a dark coloured dye which is still used in craft.

In Europe the tree is planted as an ornamental. 

Threats

The young tree can be devastated by the grey squirrel. It also susceptible to walnut leaf blotch.

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