Introduction

This page includes three sample dichotomous keys 1. for leafy trees (deciduous) illustrated and not, 2. evergreen (conifer) trees illustrated and not, and 3. illustrated tree twig identification guide. And an introduction to twig biology and anatomy.

 

 

Twigs

For many of us, when tree leaves fall for the winter, it would seem difficult or impossible to identify trees without their leaves. However tress without leaves still have enough identity to be recognized, however, it takes a bit more study to learn which tree is which from looking at their trunks and twigs.

Before we explore the basics of twig anatomy, let’s review what happens to trees across the seasons.

During the winter the reduced temperature and light slows the tree's ability to grow and produce, yet they are still alive, so when temperatures rise, oxygen goes into their twigs, through tiny pores (lenticels), and respiration increases. The flow of sap provides energy for them to grow, swell, bloom, and grow the flowers and leaves they set in their buds the previous summer.

Buds, especially those on fruit trees, contain flowers. Other buds produce stem growth and leaves. While flower and leaf buds may be found right next to each other on the same twig, they develop from different embryonic cells within the twig.

Leaves produce energy to continue to grow and any surplus is stored.

New buds, for the next year, are formed in the summer from embryonic tissues in the twig which will be the next year's growth. As the days shorten, light decreases, temperature decreases, the leaves fall and production and growth processes are slowed and the trees and it twigs take their winter forms.

Twig's winter forms are discussed as a means of tree identification next.

Winter twig anatomy

The most noticeable feature in the winter is a terminal bud at the end of each branch. Examination of them and their position can indicate the leaf arrangement, the previous year's growth, and the number of branches that will form in the next growing season.

Let’s review different parts and their functions.

Buds and leaf scars are the most revealing external structures of a woody twig.

Terminal buds are located at the end of the twig. When it is formed, growth ends for the season. Some trees do not have terminal buds. In these trees, the twigs keep growing until their food supply is depleted and then the twigs die back to the last lateral bud.

Lateral buds are located above each leaf scar.

The shape, size, and position of the terminal and lateral buds vary with each tree species. Buds of woody plants are usually protected by several layers of overlapping scales, which are modified leaves, the number and color of which may also be a means for identification.

Leaf scars are on the sides of the twig, they mark the places where the leaf stems were attached. The shape, pattern, and arrangement of the leaf scars varies on different trees. Inside each leaf scar are small fibrovascular bundles or veins. These bundles are the route by which nutrients and water molecules move to the leaf, and the sugars manufactured in the leaf move down to the stem and roots of the tree. Bundle scars are usually quite noticeable and have a definite arrangement and number for each different tree.

Nodes are the places where leaf scars are found on the twig.

• Two leaf scars at a node means there were two leaves in an opposite arrangement.
• Three leaf scars at each node, means there were the leaves in a whorled arrangement.
• If there is only one leaf scar per node, the next leaf scar will occur as an alternate arrangement on the twig.

Internode is the distance between each node.

In the cross section of a twig, the center area is made up of storage cells called the pith. In walnut, tulip, and butternut trees, the pith is divided into sections or chambers; whereas in the cottonwood and chestnut trees, the pith is five-sided, or star-shaped. This observation, along with observation of the buds, leaf scars, and bundle scars, enables us to identify many trees in our environment.

Find out more about trees in the winter in books such as Winter Botany by William Trelease.

 

Collecting samples

When collecting samples, make sure it is permissible to do so. Then select twigs that are well formed and about 8-10 inches long. Twigs which are located on the tree where they would potentially be pruned in the spring. For example twigs that grow on the underside of a branch or or in the middle of the tree on or close to the trunk.

Attach a masking tape tag to it and label the location and date it was gathered. If known write the common name and scientific name. if not, then leave room for it to be added later.

Select a twig and use the anatomy information to observe and record information and make a sketch and take notes for the following.

 

To identify the tree you can use a twig guide similar to the dichotomous leaf guides above. Like the sample below or one in the Winter Botany book or other guide.

 

 

Deciduous tree twig dichotomous identification guide with drawings