Tree ID by pinnate leaf

There are two types of Broadleaf tree leaves. They may be simple or compound. A simple leaf is made up of one piece. It is undivided. A compound leaf is divided into several leaflets.  Pinnate  is a term used to describe a compound  leaf that has leaflets  arranged in 2 rows either side of a midrib like a feather.  Leaflets may be tooth-edged or smooth edged. Many trees have pinnate leaves which are easy to recognise.

Tree ID by pinnate leaf – Here are 5 photos of tooth-edged pinnate leaves and 5 photos of smooth-edged pinnate leaves. Click on any image to enlarge it. Click on any name in red to get a full description of the tree. To go back to Tree Identification Keys click HERE. To go back to the Broadleaf Leaf Key click HERE.  

Elder leaf

Elder 5 to 7 tooth-edged leaflets

Rowan leaf

Rowan up to 15 tooth-edged leaflets

Common Ash leaf

Ash 9-13 tooth-edged leaflets

Box Elder leaf

Box Elder 3 to 7 tooth-edged leaflets

Black Walnut leaf

Golden Rain Tree 11 to 13 tooth-edged leaflets

Claret Ash leaf

Claret/Narrow-leaved Ash 7 fine tooth-edged leaflets

Manna Ash 3 to 9  broad fine tooth-edged leaflets

False Acacia leaf

False Acacia 9 to 23 smooth-edged leaflets

Common Walnut leaf

Common Walnut 5 to 13 smooth-edged leaflets

Black Walnut 10 to 23 (usually 15) tooth-edged leaflets

Tree of Heaven leaf

Tree of Heaven 11 or more smooth-edged leaflets

On broadleaf tree leaves the leaf stalk is referred to as a petiole by botanists. The petiole connects the leaf to the shoot. If the leaf has no petiole and sits right on the shoot it is known as sessile. The leaf blade is divided down the centre by the midrib. This is the central or main vein of the leaf. The veins are tubes that carry water and nutrients to and from the leaf surface. The network of veins reaches every part of the leaf surface. The leaf blade is also referred to as the lamina. The edge of the lamina is called the leaf margin. The shape of the leaf is determined by how the margin and the veins develop and is under precise genetic control. 

The margin may be smooth, toothed or lobed. There are growth points along the margin which are aligned with veins. Smooth margins grow at a uniform rate  but toothed leaves have parts of the margin that are distant from the growth points and lag behind resulting in the formation of teeth. If the growth between the tips is inhibited even more, a lobe is formed. A lobe is a rounded or pointed segment of a leaf that is separated from other segments by a gap that does not reach the midrib of the leaf. Lobes may be arranged on either side of a central axis like a feather. This leaf is ‘pinnately lobed’, or lobes may spread radially from a point like a hand.This leaf is ‘palmately lobed’. If the gap reaches the midrib the leaf is ‘palmate’. If growth between tips is further inhibited a ‘pinnate’ leaf may be formed. This has individual leaflets arranged either side of a midrib like a feather.

The shape and colour of the leaf, the number and arrangement of the veins, the size and complexity of the teeth and the shape and arrangement of the lobes are genetically controlled and offer an excellent means of identifying trees.