Black Walnut
Juglans nigra · Juglandaceae · Deciduous
Black walnut is unmistakable in autumn because of the fruit — heavy green spheres that thud onto lawns and cars. It also produces juglone, a compound that suppresses many other plants growing beneath it, which is why gardens under walnuts struggle.
Quick facts
- Arrangement
- alternate
- Leaf
- Long compound leaves with 15 to 23 toothed leaflets, often with the terminal leaflet missing or stunted.
- Bark
- Very dark grey-brown to nearly black, deeply furrowed into a rough diamond pattern.
- Fruit
- A green tennis-ball-sized husk containing a hard corrugated nut. The husk stains hands and clothing dark brown and does not wash out.
- Height
- 50–90 ft
How to confirm it
- Green husked nuts the size of a tennis ball, staining everything they touch.
- Many leaflets — 15 or more — on an alternate compound leaf.
- Crushed leaves have a distinct spicy citrus smell.
- Chambered pith: cut a twig lengthwise and the centre is divided into ladder-like compartments.
What it is confused with
One observation settles each of these.
Tree of heaven leaflets have one or two blunt teeth near the base only and smell strongly unpleasant when crushed.
Ash leaves are opposite; walnut leaves are alternate. Check that before anything else.
Where it grows
Eastern and central North America, in rich bottomland soil and widely planted for timber and nuts.
Start here: opposite or alternate?
Look at where the leaves join the twig. Are they in matched pairs directly across from each other, or staggered one after another? The vast majority of trees are alternate, so finding an opposite tree removes almost everything else in one step.
In North America, opposite-leaved trees are remembered as MAD Cap Horse: Maple, Ash, Dogwood, Caprifoliaceae (viburnums and elders), and Horse chestnut. That is very nearly the whole list.
Check partway along a healthy twig rather than at the tip, where crowding can make alternate leaves look paired. And check more than one twig.