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Walnut tree

Juglans species

Identified this tree? Record it for the urban tree survey.

ID check

  1. Leaves are alternate in arrangement and pinnately divided into separate leaflets.
  2. Twigs are not velvety hairy or thorny.
  3. Twigs have distinctive Y-shaped scars where the leaves have fallen. Cut twigs leak latex.
  4. The flowers are in catkins or short clusters.

Description

Walnut tree

Walnut tree © Università di Trieste, Dipartimento di Biologia. Photo: Andrea Moro

Tree

Tall and wide-spreading, up to 50m high.

Bark

Grey, dark brown or black. Smooth but eventually becoming cracked and fissured.

Twigs

Have a central pith divided into chambers, and distinctive Y-shaped scars where the leaves have fallen.

Leaves

Divided into 7–9 or 15–23 leaflets, depending on the species.

Leaflets

They are 6–15cm long. Those towards the tip of the leaf are larger than those towards the base.

Flowers

Male flowers are in catkins, female flowers in short, spike-like clusters of 2–5 on the same tree.

Fruit

They are 3.5–5cm long, globe-shaped or slightly pear-shaped and hairy. The thick green husk contains a wrinkled or ridged stone - the familiar walnut.

Images

Walnut tree twig

Walnut tree twig, with Y-shaped scars where the leaves have fallen.

© Rasbak, Creative Commons Attribution-Share Alike 3.0
Walnut tree leaves

Walnut tree leaves, divided into 3 or more leaflets.

© Università di Trieste, Dipartimento di Biologia. Photo: Andrea Moro
Walnut tree flowers

Walnut tree flowers in catkins.

© Robert Vidéki, Doronicum Kft., Hungary
Walnut tree

Walnut tree.

© Università di Trieste, Dipartimento di Biologia. Photo: Andrea Moro

Diagrams

These diagrams explain some of the important tree and plant parts.

Flower

Diagram of a flower showing the stigma, stamen, style, petal and sepal

Leaf parts

Diagram of a leaf showing the apex, margin, midrib, vein and stalk

Leaf shapes

These diagrams show the different leaf shapes you might come across on your survey. Leaf shapes are important for identifying trees.

Palmate leaf
A palmate leaf - the leaflets extend from a single point, like fingers from a hand
Palmately lobed leaf
Palmately lobed leaf - the lobes are arranged on both sides of the stalk like a feather
Pinnate leaf
Pinnate leaf - the leaflets are arranged on both sides of the stalk like a feather
Pinnately lobed leaf
Pinnately lobed leaf - the lobes are arranged on both sides of the stalk like a feather

Leaf arrangements

The way leaves are arranged on a stem can be important for identifying trees.

Opposite leaves
Opposite leaf arrangement
Alternate leaves
Alternate leaf arrangement

Glossary

These definitions explain some of the trickier words and phrases used in these pages.

Alternate – the arrangement of leaves on a stem - the leaves attach at different but alternating points, rather than opposite points.

Anther – the part of the stamen that contains pollen.

Apex – the top or end; the tip of a leaf for example.

Bract – a leaf-like structure, usually found below the flower or fruit.

Bud scale – usually a type of modified leaf that encloses and protects a bud.

Catkin – slender inflorescences made up of small flowers, usually reduced to the male and female parts. Catkins are typical of wind-pollinated trees.

Coniferous – trees that have cones, and needle or scale-like leaves.

Crown – in a tree, everything above the trunk.

Deciduous – a tree that sheds its leaves all at once in the autumn.

Evergreen – a tree that retains its leaves all year round.

Girth – the circumference of something, like the trunk of a tree.

Gland (of a leaf) – a small organ on a leaf that gives out oils or similar substances.

Inflorescence – the arrangement of all the flowers on a tree. The shape is used to help identify the plant.

Key – a tool used to identify groups and species of living things.

Leaflet – a subdivision of a leaf - it may look like a leaf but is attached to the leaf stalk or midrib, not to the shoot.

Lobe – a rounded or pointed section of a leaf, not divided into a leaflet.

Margin – the edge of a leaf.

Midrib – the central vein of a leaf.

Native – a tree that occurs naturally in an area, as opposed to a non-native tree that has been introduced.

Opposite – the arrangement of leaves on a stem - the leaves attach in pairs at the same point, opposite each other, rather than attaching at alternate points.

Palmate – a leaf shape in which the lobes or leaflets radiate from a single point, like fingers from a hand.

Petals – usually larger and more brightly coloured than sepals.

Pinnate – a leaf shape in which the lobes or leaflets are arranged on both sides of the stalk or midrib like a feather.

Pollarded – when the upper branches of a tree have been cut back to encourage new growth.

Sepals – the outermost parts of a flower which cover and protect the flower when it is in bud. They are usually green.

Side shoots – short, spur-like shoots growing from the main shoots.

Spike – an elongated cluster of flowers; a type of inflorescence.

Stalk – the structure that supports the blade of a leaf.

Stigma – the part at the end of the style. It is covered with a sticky substance that pollen adheres to.

Stipule – a small, leaf-like structure, found where the leaf connects to the stem.

Style – a tube-like structure in the centre of a flower that supports the stigma.

Trunk – the woody stem of a tree, before the branches.

Urban forest – the trees in our towns and cities.

Whorl – 3 or more leaves or needles circling around a stem.

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